|
(New thread due to very incorrect subject line and opening paragraph in previous thread.)
I still have not determined why DS101 will not turn on in my HP-1421A time-base.? I can ground Q109's base through a resistor and force the lamp to turn on.? I can place a 1K resistor in parallel with R137 and also force the lamp to turn on; however, nothing else works. ?I thought that the neon might have aged to the point where there isn't sufficient striking voltage for it but since it will turn on with these methods, that doesn't seem to be case(?).
Setting the unit up as described in the manual for voltage tests, I get the following:
-100V F(B): -99.9V
Q109 Emitter: -9.35V Base: -8.78V Collector: -0.33V
Q110 Emitter: -8.01V Base: -8.11V Collector: -3.7V
Given those values, it would appear (at least to me) that the lamp should turn on but it doesn't.
As a test, I disconnected R136/DS101 (the yellow (4) wire) from the board and connected a battery, resistor, and LED between GND and the collector of Q109.? This works just as it should (i.e. the LED turns on when the sweep is triggered, turns off at the end of the sweep, and repeats that).
Is it possible that Q109 is not able to conduct enough current to turn DS101 on but enough to make the LED work?? That seems unlikely but, at this point, I don't have any other explanation.
Any help with this is appreciated.
Thanks,
Barry - N4BUQ
|
On 4/14/2024 8:59 PM, n4buq wrote: (New thread due to very incorrect subject line and opening paragraph in previous thread.)
I still have not determined why DS101 will not turn on in my HP-1421A time-base.? I can ground Q109's base through a resistor and force the lamp to turn on.? I can place a 1K resistor in parallel with R137 and also force the lamp to turn on; however, nothing else works. I thought that the neon might have aged to the point where there isn't sufficient striking voltage for it but since it will turn on with these methods, that doesn't seem to be case(?).
If you can turn it on, it's not bad.? If you can provide a signal to the transistor that turns it on, it's likely not bad. Where does the signal come from, is it there when it is supposed to be? Harvey Setting the unit up as described in the manual for voltage tests, I get the following:
-100V F(B): -99.9V
Q109
Emitter: -9.35V
Base: -8.78V
Collector: -0.33V
Q110
Emitter: -8.01V
Base: -8.11V
Collector: -3.7V
Given those values, it would appear (at least to me) that the lamp should turn on but it doesn't.
As a test, I disconnected R136/DS101 (the yellow (4) wire) from the board and connected a battery, resistor, and LED between GND and the collector of Q109.? This works just as it should (i.e. the LED turns on when the sweep is triggered, turns off at the end of the sweep, and repeats that).
Is it possible that Q109 is not able to conduct enough current to turn DS101 on but enough to make the LED work?? That seems unlikely but, at this point, I don't have any other explanation.
Any help with this is appreciated.
Thanks,
Barry - N4BUQ
|
Let's go real simple.? You report the collector of Q109 is at essentially ground, right?
So if you ground it, and ASSUMING R135 AND R136 HAVEN'T DRIFTED, the neon should see 86.9 volts, which should light it.
Neons when new fire somewhere in the 65 volt range but when old can easily drift upwards, even higher than that voltage.? And resistors can and do drift out of tolerance.
Check R135 and R136 values.? Then ground Q109 collector and measure the junction of R135 and R136 voltage.? If you see near 86.9 volts your neon is old and has too high a firing voltage.
Quick and dirty, try lifting one lead of R136 and see if the neon lights then.
Peter
toggle quoted message
Show quoted text
On 4/14/2024 8:59 PM, n4buq via groups.io wrote: (New thread due to very incorrect subject line and opening paragraph in previous thread.)
I still have not determined why DS101 will not turn on in my HP-1421A time-base.? I can ground Q109's base through a resistor and force the lamp to turn on.? I can place a 1K resistor in parallel with R137 and also force the lamp to turn on; however, nothing else works. I thought that the neon might have aged to the point where there isn't sufficient striking voltage for it but since it will turn on with these methods, that doesn't seem to be case(?).
Setting the unit up as described in the manual for voltage tests, I get the following:
-100V F(B): -99.9V
Q109
Emitter: -9.35V
Base: -8.78V
Collector: -0.33V
Q110
Emitter: -8.01V
Base: -8.11V
Collector: -3.7V
Given those values, it would appear (at least to me) that the lamp should turn on but it doesn't.
As a test, I disconnected R136/DS101 (the yellow (4) wire) from the board and connected a battery, resistor, and LED between GND and the collector of Q109.? This works just as it should (i.e. the LED turns on when the sweep is triggered, turns off at the end of the sweep, and repeats that).
Is it possible that Q109 is not able to conduct enough current to turn DS101 on but enough to make the LED work?? That seems unlikely but, at this point, I don't have any other explanation.
Any help with this is appreciated.
Thanks,
Barry - N4BUQ
|
I'm not sure exactly what you're asking about.? The signal on Q109's base is tied to the base of 1/2 of a Schmitt Trigger through R140.? Aside from the fact that the schematic has the wrong value (it should be -8.8V, not +8.8V), most of the values are quite close. The one one that is significantly different is Q109's collector.? I presume that with -8.8V on the base and -9.4V on the emitter, then Q109 is fully forward-biased so its collector would be at two diode-drops above the emitter - at least that's how I see it and it explains the value I'm seeing.
Here's a larger snippet if it helps:
Thanks, Barry - N4BUQ
(New thread due to very incorrect subject line and opening paragraph in previous thread.) I still have not determined why DS101 will not turn on in my HP-1421A time-base.? I can ground Q109's base through a resistor and force the lamp to turn on.? I can place a 1K resistor in parallel with R137 and also force the lamp to turn on; however, nothing else works. ?I thought that the neon might have aged to the point where there isn't sufficient striking voltage for it but since it will turn on with these methods, that doesn't seem to be case(?). Setting the unit up as described in the manual for voltage tests, I get the following:
-100V F(B): -99.9V
Q109 Emitter: -9.35V Base: -8.78V Collector: -0.33V
Q110 Emitter: -8.01V Base: -8.11V Collector: -3.7V
Given those values, it would appear (at least to me) that the lamp should turn on but it doesn't.
As a test, I disconnected R136/DS101 (the yellow (4) wire) from the board and connected a battery, resistor, and LED between GND and the collector of Q109.? This works just as it should (i.e. the LED turns on when the sweep is triggered, turns off at the end of the sweep, and repeats that).
Is it possible that Q109 is not able to conduct enough current to turn DS101 on but enough to make the LED work?? That seems unlikely but, at this point, I don't have any other explanation.
Any help with this is appreciated.
Thanks,
Barry - N4BUQ
|
I'll try grounding the collector of Q109. Unfortunately, lifting one lead of R136 isn't quick. The front panel has to be removed to gain access to the small assembly that holds DS101, R135, and R136. It's too cramped to get to it from the back side of the front of the chassis.
Thanks,
Barry - N4BUQ
toggle quoted message
Show quoted text
----- Original Message ----- From: "Peter Gottlieb" <hpnpilot@...>
To: "HP-Agilent-Keysight-equipment" <[email protected]>
Sent: Sunday, April 14, 2024 8:10:33 PM
Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the Malfunctioning Time Base RESET Lamp in my
HP-1421A. Let's go real simple.? You report the collector of Q109 is at essentially
ground, right?
So if you ground it, and ASSUMING R135 AND R136 HAVEN'T DRIFTED, the neon should
see 86.9 volts, which should light it.
Neons when new fire somewhere in the 65 volt range but when old can easily drift
upwards, even higher than that voltage.? And resistors can and do drift out of
tolerance.
Check R135 and R136 values.? Then ground Q109 collector and measure the junction
of R135 and R136 voltage.? If you see near 86.9 volts your neon is old and has
too high a firing voltage.
Quick and dirty, try lifting one lead of R136 and see if the neon lights then.
Peter
On 4/14/2024 8:59 PM, n4buq via groups.io wrote:
(New thread due to very incorrect subject line and opening paragraph in
previous thread.)
I still have not determined why DS101 will not turn on in my HP-1421A
time-base.? I can ground Q109's base through a resistor and force the lamp to
turn on.? I can place a 1K resistor in parallel with R137 and also force the
lamp to turn on; however, nothing else works. I thought that the neon might
have aged to the point where there isn't sufficient striking voltage for it
but since it will turn on with these methods, that doesn't seem to be case(?).
Setting the unit up as described in the manual for voltage tests, I get the
following:
-100V F(B): -99.9V
Q109
Emitter: -9.35V
Base: -8.78V
Collector: -0.33V
Q110
Emitter: -8.01V
Base: -8.11V
Collector: -3.7V
Given those values, it would appear (at least to me) that the lamp should turn
on but it doesn't.
As a test, I disconnected R136/DS101 (the yellow (4) wire) from the board and
connected a battery, resistor, and LED between GND and the collector of Q109.
This works just as it should (i.e. the LED turns on when the sweep is
triggered, turns off at the end of the sweep, and repeats that).
Is it possible that Q109 is not able to conduct enough current to turn DS101
on but enough to make the LED work?? That seems unlikely but, at this point, I
don't have any other explanation.
Any help with this is appreciated.
Thanks,
Barry - N4BUQ
|
BTW, when I placed the 1K across R137, that gave it enough of a path to ground through R139 as well as to -12.6V through R138 to make it light up so I presume grounding Q109's base will cause it to light up as well but will do that anyway.
Thanks,
Barry - N4BUQ
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Show quoted text
----- Original Message ----- From: "n4buq" <n4buq@...>
To: "HP-Agilent-Keysight-equipment" <[email protected]>
Sent: Sunday, April 14, 2024 8:55:06 PM
Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the Malfunctioning Time Base RESET Lamp in my
HP-1421A. I'll try grounding the collector of Q109. Unfortunately, lifting one lead of
R136 isn't quick. The front panel has to be removed to gain access to the
small assembly that holds DS101, R135, and R136. It's too cramped to get to it
from the back side of the front of the chassis.
Thanks,
Barry - N4BUQ
----- Original Message -----
From: "Peter Gottlieb" <hpnpilot@...>
To: "HP-Agilent-Keysight-equipment" <[email protected]>
Sent: Sunday, April 14, 2024 8:10:33 PM
Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the
Malfunctioning Time Base RESET Lamp in my
HP-1421A. Let's go real simple.? You report the collector of Q109 is at essentially
ground, right?
So if you ground it, and ASSUMING R135 AND R136 HAVEN'T DRIFTED, the neon should
see 86.9 volts, which should light it.
Neons when new fire somewhere in the 65 volt range but when old can easily drift
upwards, even higher than that voltage.? And resistors can and do drift out of
tolerance.
Check R135 and R136 values.? Then ground Q109 collector and measure the junction
of R135 and R136 voltage.? If you see near 86.9 volts your neon is old and has
too high a firing voltage.
Quick and dirty, try lifting one lead of R136 and see if the neon lights then.
Peter
On 4/14/2024 8:59 PM, n4buq via groups.io wrote:
(New thread due to very incorrect subject line and opening paragraph in
previous thread.)
I still have not determined why DS101 will not turn on in my HP-1421A
time-base.? I can ground Q109's base through a resistor and force the lamp to
turn on.? I can place a 1K resistor in parallel with R137 and also force the
lamp to turn on; however, nothing else works. I thought that the neon might
have aged to the point where there isn't sufficient striking voltage for it
but since it will turn on with these methods, that doesn't seem to be case(?).
Setting the unit up as described in the manual for voltage tests, I get the
following:
-100V F(B): -99.9V
Q109
Emitter: -9.35V
Base: -8.78V
Collector: -0.33V
Q110
Emitter: -8.01V
Base: -8.11V
Collector: -3.7V
Given those values, it would appear (at least to me) that the lamp should turn
on but it doesn't.
As a test, I disconnected R136/DS101 (the yellow (4) wire) from the board and
connected a battery, resistor, and LED between GND and the collector of Q109.
This works just as it should (i.e. the LED turns on when the sweep is
triggered, turns off at the end of the sweep, and repeats that).
Is it possible that Q109 is not able to conduct enough current to turn DS101
on but enough to make the LED work?? That seems unlikely but, at this point, I
don't have any other explanation.
Any help with this is appreciated.
Thanks,
Barry - N4BUQ
|
Argh!! I meant grounding Q109's collector (although grounding the base through a resistor has also shown the bulb will light as well). I think I may need to stop typing today...
Barry - N4BUQ
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Show quoted text
BTW, when I placed the 1K across R137, that gave it enough of a path to ground
through R139 as well as to -12.6V through R138 to make it light up so I presume
grounding Q109's base will cause it to light up as well but will do that
anyway.
Thanks,
Barry - N4BUQ
----- Original Message -----
From: "n4buq" <n4buq@...>
To: "HP-Agilent-Keysight-equipment" <[email protected]>
Sent: Sunday, April 14, 2024 8:55:06 PM
Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the
Malfunctioning Time Base RESET Lamp in my
HP-1421A. I'll try grounding the collector of Q109. Unfortunately, lifting one lead of
R136 isn't quick. The front panel has to be removed to gain access to the
small assembly that holds DS101, R135, and R136. It's too cramped to get to it
from the back side of the front of the chassis.
Thanks,
Barry - N4BUQ
----- Original Message -----
From: "Peter Gottlieb" <hpnpilot@...>
To: "HP-Agilent-Keysight-equipment" <[email protected]>
Sent: Sunday, April 14, 2024 8:10:33 PM
Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the
Malfunctioning Time Base RESET Lamp in my
HP-1421A. Let's go real simple.? You report the collector of Q109 is at essentially
ground, right?
So if you ground it, and ASSUMING R135 AND R136 HAVEN'T DRIFTED, the neon should
see 86.9 volts, which should light it.
Neons when new fire somewhere in the 65 volt range but when old can easily drift
upwards, even higher than that voltage.? And resistors can and do drift out of
tolerance.
Check R135 and R136 values.? Then ground Q109 collector and measure the junction
of R135 and R136 voltage.? If you see near 86.9 volts your neon is old and has
too high a firing voltage.
Quick and dirty, try lifting one lead of R136 and see if the neon lights then.
Peter
On 4/14/2024 8:59 PM, n4buq via groups.io wrote:
(New thread due to very incorrect subject line and opening paragraph in
previous thread.)
I still have not determined why DS101 will not turn on in my HP-1421A
time-base.? I can ground Q109's base through a resistor and force the lamp to
turn on.? I can place a 1K resistor in parallel with R137 and also force the
lamp to turn on; however, nothing else works. I thought that the neon might
have aged to the point where there isn't sufficient striking voltage for it
but since it will turn on with these methods, that doesn't seem to be case(?).
Setting the unit up as described in the manual for voltage tests, I get the
following:
-100V F(B): -99.9V
Q109
Emitter: -9.35V
Base: -8.78V
Collector: -0.33V
Q110
Emitter: -8.01V
Base: -8.11V
Collector: -3.7V
Given those values, it would appear (at least to me) that the lamp should turn
on but it doesn't.
As a test, I disconnected R136/DS101 (the yellow (4) wire) from the board and
connected a battery, resistor, and LED between GND and the collector of Q109.
This works just as it should (i.e. the LED turns on when the sweep is
triggered, turns off at the end of the sweep, and repeats that).
Is it possible that Q109 is not able to conduct enough current to turn DS101
on but enough to make the LED work?? That seems unlikely but, at this point, I
don't have any other explanation.
Any help with this is appreciated.
Thanks,
Barry - N4BUQ
|
If you can lift Q109C then you could at least measure the sum of those two resistors.? But it would be nice to be able to measure the junction of them.
toggle quoted message
Show quoted text
On 4/14/2024 9:55 PM, n4buq via groups.io wrote: I'll try grounding the collector of Q109. Unfortunately, lifting one lead of R136 isn't quick. The front panel has to be removed to gain access to the small assembly that holds DS101, R135, and R136. It's too cramped to get to it from the back side of the front of the chassis.
Thanks,
Barry - N4BUQ
----- Original Message -----
From: "Peter Gottlieb" <hpnpilot@...>
To: "HP-Agilent-Keysight-equipment" <[email protected]>
Sent: Sunday, April 14, 2024 8:10:33 PM
Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the Malfunctioning Time Base RESET Lamp in my
HP-1421A.
Let's go real simple.? You report the collector of Q109 is at essentially
ground, right?
So if you ground it, and ASSUMING R135 AND R136 HAVEN'T DRIFTED, the neon should
see 86.9 volts, which should light it.
Neons when new fire somewhere in the 65 volt range but when old can easily drift
upwards, even higher than that voltage.? And resistors can and do drift out of
tolerance.
Check R135 and R136 values.? Then ground Q109 collector and measure the junction
of R135 and R136 voltage.? If you see near 86.9 volts your neon is old and has
too high a firing voltage.
Quick and dirty, try lifting one lead of R136 and see if the neon lights then.
Peter
On 4/14/2024 8:59 PM, n4buq via groups.io wrote:
(New thread due to very incorrect subject line and opening paragraph in
previous thread.)
I still have not determined why DS101 will not turn on in my HP-1421A
time-base.? I can ground Q109's base through a resistor and force the lamp to
turn on.? I can place a 1K resistor in parallel with R137 and also force the
lamp to turn on; however, nothing else works. I thought that the neon might
have aged to the point where there isn't sufficient striking voltage for it
but since it will turn on with these methods, that doesn't seem to be case(?).
Setting the unit up as described in the manual for voltage tests, I get the
following:
-100V F(B): -99.9V
Q109
Emitter: -9.35V
Base: -8.78V
Collector: -0.33V
Q110
Emitter: -8.01V
Base: -8.11V
Collector: -3.7V
Given those values, it would appear (at least to me) that the lamp should turn
on but it doesn't.
As a test, I disconnected R136/DS101 (the yellow (4) wire) from the board and
connected a battery, resistor, and LED between GND and the collector of Q109.
This works just as it should (i.e. the LED turns on when the sweep is
triggered, turns off at the end of the sweep, and repeats that).
Is it possible that Q109 is not able to conduct enough current to turn DS101
on but enough to make the LED work?? That seems unlikely but, at this point, I
don't have any other explanation.
Any help with this is appreciated.
Thanks,
Barry - N4BUQ
|
IIRC, when I had the front panel off for cleaning, I inspected those and I _think_ they were very close. Although I don't know why, they used 1% resistors there. Of course, that doesn't prevent them from drifting but I do think they were quite close to spec.
Thanks,
Barry - N4BUQ
toggle quoted message
Show quoted text
----- Original Message ----- From: "Peter Gottlieb" <hpnpilot@...>
To: "HP-Agilent-Keysight-equipment" <[email protected]>
Sent: Sunday, April 14, 2024 9:07:32 PM
Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the Malfunctioning Time Base RESET Lamp in my
HP-1421A. If you can lift Q109C then you could at least measure the sum of those two
resistors.? But it would be nice to be able to measure the junction of them.
On 4/14/2024 9:55 PM, n4buq via groups.io wrote:
I'll try grounding the collector of Q109. Unfortunately, lifting one lead of
R136 isn't quick. The front panel has to be removed to gain access to the
small assembly that holds DS101, R135, and R136. It's too cramped to get to it
from the back side of the front of the chassis.
Thanks,
Barry - N4BUQ
----- Original Message -----
From: "Peter Gottlieb" <hpnpilot@...>
To: "HP-Agilent-Keysight-equipment" <[email protected]>
Sent: Sunday, April 14, 2024 8:10:33 PM
Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the
Malfunctioning Time Base RESET Lamp in my
HP-1421A.
Let's go real simple.? You report the collector of Q109 is at essentially
ground, right?
So if you ground it, and ASSUMING R135 AND R136 HAVEN'T DRIFTED, the neon should
see 86.9 volts, which should light it.
Neons when new fire somewhere in the 65 volt range but when old can easily drift
upwards, even higher than that voltage.? And resistors can and do drift out of
tolerance.
Check R135 and R136 values.? Then ground Q109 collector and measure the junction
of R135 and R136 voltage.? If you see near 86.9 volts your neon is old and has
too high a firing voltage.
Quick and dirty, try lifting one lead of R136 and see if the neon lights then.
Peter
On 4/14/2024 8:59 PM, n4buq via groups.io wrote:
(New thread due to very incorrect subject line and opening paragraph in
previous thread.)
I still have not determined why DS101 will not turn on in my HP-1421A
time-base.? I can ground Q109's base through a resistor and force the lamp to
turn on.? I can place a 1K resistor in parallel with R137 and also force the
lamp to turn on; however, nothing else works. I thought that the neon might
have aged to the point where there isn't sufficient striking voltage for it
but since it will turn on with these methods, that doesn't seem to be case(?).
Setting the unit up as described in the manual for voltage tests, I get the
following:
-100V F(B): -99.9V
Q109
Emitter: -9.35V
Base: -8.78V
Collector: -0.33V
Q110
Emitter: -8.01V
Base: -8.11V
Collector: -3.7V
Given those values, it would appear (at least to me) that the lamp should turn
on but it doesn't.
As a test, I disconnected R136/DS101 (the yellow (4) wire) from the board and
connected a battery, resistor, and LED between GND and the collector of Q109.
This works just as it should (i.e. the LED turns on when the sweep is
triggered, turns off at the end of the sweep, and repeats that).
Is it possible that Q109 is not able to conduct enough current to turn DS101
on but enough to make the LED work?? That seems unlikely but, at this point, I
don't have any other explanation.
Any help with this is appreciated.
Thanks,
Barry - N4BUQ
|
Barry, what happens when you go to Single Sweep and press Reset switch S105??
My schematic (and yours) shows the Collector of Q109 at +48V but your measurement shows -0.33V??
IIRC, when I had the front panel off for cleaning, I inspected those and I _think_ they were very close.? Although I don't know why, they used 1% resistors there.? Of course, that doesn't prevent them from drifting but I do think they were quite close to spec.
Thanks,
Barry - N4BUQ
----- Original Message -----
> From: "Peter Gottlieb" <hpnpilot@...>
> To: "HP-Agilent-Keysight-equipment" <[email protected]>
> Sent: Sunday, April 14, 2024 9:07:32 PM
> Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the Malfunctioning Time Base RESET Lamp in my
> HP-1421A.
> If you can lift Q109C then you could at least measure the sum of those two
> resistors.? But it would be nice to be able to measure the junction of them.
>
> On 4/14/2024 9:55 PM, n4buq via wrote:
>> I'll try grounding the collector of Q109.? Unfortunately, lifting one lead of
>> R136 isn't quick.? The front panel has to be removed to gain access to the
>> small assembly that holds DS101, R135, and R136.? It's too cramped to get to it
>> from the back side of the front of the chassis.
>>
>> Thanks,
>> Barry - N4BUQ
>>
>> ----- Original Message -----
>>> From: "Peter Gottlieb" <hpnpilot@...>
>>> To: "HP-Agilent-Keysight-equipment" <[email protected]>
>>> Sent: Sunday, April 14, 2024 8:10:33 PM
>>> Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the
>>> Malfunctioning Time Base RESET Lamp in my
>>> HP-1421A.
>>> Let's go real simple.? You report the collector of Q109 is at essentially
>>> ground, right?
>>>
>>> So if you ground it, and ASSUMING R135 AND R136 HAVEN'T DRIFTED, the neon should
>>> see 86.9 volts, which should light it.
>>>
>>> Neons when new fire somewhere in the 65 volt range but when old can easily drift
>>> upwards, even higher than that voltage.? And resistors can and do drift out of
>>> tolerance.
>>>
>>> Check R135 and R136 values.? Then ground Q109 collector and measure the junction
>>> of R135 and R136 voltage.? If you see near 86.9 volts your neon is old and has
>>> too high a firing voltage.
>>>
>>> Quick and dirty, try lifting one lead of R136 and see if the neon lights then.
>>>
>>> Peter
>>>
>>>
>>> On 4/14/2024 8:59 PM, n4buq via wrote:
>>>> (New thread due to very incorrect subject line and opening paragraph in
>>>> previous thread.)
>>>>
>>>> I still have not determined why DS101 will not turn on in my HP-1421A
>>>> time-base.? I can ground Q109's base through a resistor and force the lamp to
>>>> turn on.? I can place a 1K resistor in parallel with R137 and also force the
>>>> lamp to turn on; however, nothing else works. I thought that the neon might
>>>> have aged to the point where there isn't sufficient striking voltage for it
>>>> but since it will turn on with these methods, that doesn't seem to be case(?).
>>>>
>>>> Setting the unit up as described in the manual for voltage tests, I get the
>>>> following:
>>>>
>>>> -100V F(B): -99.9V
>>>>
>>>> Q109
>>>> Emitter: -9.35V
>>>> Base: -8.78V
>>>> Collector: -0.33V
>>>>
>>>> Q110
>>>> Emitter: -8.01V
>>>> Base: -8.11V
>>>> Collector: -3.7V
>>>>
>>>> Given those values, it would appear (at least to me) that the lamp should turn
>>>> on but it doesn't.
>>>>
>>>> As a test, I disconnected R136/DS101 (the yellow (4) wire) from the board and
>>>> connected a battery, resistor, and LED between GND and the collector of Q109.
>>>> This works just as it should (i.e. the LED turns on when the sweep is
>>>> triggered, turns off at the end of the sweep, and repeats that).
>>>>
>>>> Is it possible that Q109 is not able to conduct enough current to turn DS101
>>>> on but enough to make the LED work?? That seems unlikely but, at this point, I
>>>> don't have any other explanation.
>>>>
>>>> Any help with this is appreciated.
>>>>
>>>> Thanks,
>>>> Barry - N4BUQ
>>>>
>>>>
>>>
>>>
>>>
>>
>>
>>
>>
>
>
>
>
|
My 1421A (serial 0803A03889), when I go to Single Sweep and press Reset switch S105, the Reset neon DS101 blinks and neon V105 illuminates as long as the switch is pressed.?
Barry, what happens when you go to Single Sweep and press Reset switch S105??
My schematic (and yours) shows the Collector of Q109 at +48V but your measurement shows -0.33V??
IIRC, when I had the front panel off for cleaning, I inspected those and I _think_ they were very close.? Although I don't know why, they used 1% resistors there.? Of course, that doesn't prevent them from drifting but I do think they were quite close to spec.
Thanks,
Barry - N4BUQ
----- Original Message -----
> From: "Peter Gottlieb" <hpnpilot@...>
> To: "HP-Agilent-Keysight-equipment" <[email protected]>
> Sent: Sunday, April 14, 2024 9:07:32 PM
> Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the Malfunctioning Time Base RESET Lamp in my
> HP-1421A.
> If you can lift Q109C then you could at least measure the sum of those two
> resistors.? But it would be nice to be able to measure the junction of them.
>
> On 4/14/2024 9:55 PM, n4buq via wrote:
>> I'll try grounding the collector of Q109.? Unfortunately, lifting one lead of
>> R136 isn't quick.? The front panel has to be removed to gain access to the
>> small assembly that holds DS101, R135, and R136.? It's too cramped to get to it
>> from the back side of the front of the chassis.
>>
>> Thanks,
>> Barry - N4BUQ
>>
>> ----- Original Message -----
>>> From: "Peter Gottlieb" <hpnpilot@...>
>>> To: "HP-Agilent-Keysight-equipment" <[email protected]>
>>> Sent: Sunday, April 14, 2024 8:10:33 PM
>>> Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the
>>> Malfunctioning Time Base RESET Lamp in my
>>> HP-1421A.
>>> Let's go real simple.? You report the collector of Q109 is at essentially
>>> ground, right?
>>>
>>> So if you ground it, and ASSUMING R135 AND R136 HAVEN'T DRIFTED, the neon should
>>> see 86.9 volts, which should light it.
>>>
>>> Neons when new fire somewhere in the 65 volt range but when old can easily drift
>>> upwards, even higher than that voltage.? And resistors can and do drift out of
>>> tolerance.
>>>
>>> Check R135 and R136 values.? Then ground Q109 collector and measure the junction
>>> of R135 and R136 voltage.? If you see near 86.9 volts your neon is old and has
>>> too high a firing voltage.
>>>
>>> Quick and dirty, try lifting one lead of R136 and see if the neon lights then.
>>>
>>> Peter
>>>
>>>
>>> On 4/14/2024 8:59 PM, n4buq via wrote:
>>>> (New thread due to very incorrect subject line and opening paragraph in
>>>> previous thread.)
>>>>
>>>> I still have not determined why DS101 will not turn on in my HP-1421A
>>>> time-base.? I can ground Q109's base through a resistor and force the lamp to
>>>> turn on.? I can place a 1K resistor in parallel with R137 and also force the
>>>> lamp to turn on; however, nothing else works. I thought that the neon might
>>>> have aged to the point where there isn't sufficient striking voltage for it
>>>> but since it will turn on with these methods, that doesn't seem to be case(?).
>>>>
>>>> Setting the unit up as described in the manual for voltage tests, I get the
>>>> following:
>>>>
>>>> -100V F(B): -99.9V
>>>>
>>>> Q109
>>>> Emitter: -9.35V
>>>> Base: -8.78V
>>>> Collector: -0.33V
>>>>
>>>> Q110
>>>> Emitter: -8.01V
>>>> Base: -8.11V
>>>> Collector: -3.7V
>>>>
>>>> Given those values, it would appear (at least to me) that the lamp should turn
>>>> on but it doesn't.
>>>>
>>>> As a test, I disconnected R136/DS101 (the yellow (4) wire) from the board and
>>>> connected a battery, resistor, and LED between GND and the collector of Q109.
>>>> This works just as it should (i.e. the LED turns on when the sweep is
>>>> triggered, turns off at the end of the sweep, and repeats that).
>>>>
>>>> Is it possible that Q109 is not able to conduct enough current to turn DS101
>>>> on but enough to make the LED work?? That seems unlikely but, at this point, I
>>>> don't have any other explanation.
>>>>
>>>> Any help with this is appreciated.
>>>>
>>>> Thanks,
>>>> Barry - N4BUQ
>>>>
>>>>
>>>
>>>
>>>
>>
>>
>>
>>
>
>
>
>
|
Jeremy,
Neither NORMAL or SINGLE will cause the lamp to light but the LED lights properly in either mode.
The voltage at Q109's collector is what's puzzling me.? When I first turn it on, the voltage is somewhere close to the value on the schematic (I don't recall the exact voltage); however, after a few seconds, the voltage drops significantly to somewhere close to what I listed and if I recall, it continues to slowly drift towards zero over a period of 20 or 30 seconds.? I'm not sure what that voltage will settle to if I turn it on in SINGLE mode and no triggering event occurs.
I know that neon lamps do not need the firing voltage maintained in order to keep the lamp on but 52V seems quite low and that doesn't take into consideration how much voltage R135 drops so that would be just a bit less than 52V across the lamp.
It would be interesting to know what you see for the voltage at Q109's collector in your 1421A.
Thanks again, Barry - N4BUQ
Barry, what happens when you go to Single Sweep and press Reset switch S105??
My schematic (and yours) shows the Collector of Q109 at +48V but your measurement shows -0.33V??
IIRC, when I had the front panel off for cleaning, I inspected those and I _think_ they were very close.? Although I don't know why, they used 1% resistors there.? Of course, that doesn't prevent them from drifting but I do think they were quite close to spec.
Thanks,
Barry - N4BUQ
----- Original Message -----
> From: "Peter Gottlieb" <hpnpilot@...>
> To: "HP-Agilent-Keysight-equipment" <[email protected]>
> Sent: Sunday, April 14, 2024 9:07:32 PM
> Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the Malfunctioning Time Base RESET Lamp in my
> HP-1421A.
> If you can lift Q109C then you could at least measure the sum of those two
> resistors.? But it would be nice to be able to measure the junction of them.
>
> On 4/14/2024 9:55 PM, n4buq via wrote:
>> I'll try grounding the collector of Q109.? Unfortunately, lifting one lead of
>> R136 isn't quick.? The front panel has to be removed to gain access to the
>> small assembly that holds DS101, R135, and R136.? It's too cramped to get to it
>> from the back side of the front of the chassis.
>>
>> Thanks,
>> Barry - N4BUQ
>>
>> ----- Original Message -----
>>> From: "Peter Gottlieb" <hpnpilot@...>
>>> To: "HP-Agilent-Keysight-equipment" <[email protected]>
>>> Sent: Sunday, April 14, 2024 8:10:33 PM
>>> Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the
>>> Malfunctioning Time Base RESET Lamp in my
>>> HP-1421A.
>>> Let's go real simple.? You report the collector of Q109 is at essentially
>>> ground, right?
>>>
>>> So if you ground it, and ASSUMING R135 AND R136 HAVEN'T DRIFTED, the neon should
>>> see 86.9 volts, which should light it.
>>>
>>> Neons when new fire somewhere in the 65 volt range but when old can easily drift
>>> upwards, even higher than that voltage.? And resistors can and do drift out of
>>> tolerance.
>>>
>>> Check R135 and R136 values.? Then ground Q109 collector and measure the junction
>>> of R135 and R136 voltage.? If you see near 86.9 volts your neon is old and has
>>> too high a firing voltage.
>>>
>>> Quick and dirty, try lifting one lead of R136 and see if the neon lights then.
>>>
>>> Peter
>>>
>>>
>>> On 4/14/2024 8:59 PM, n4buq via wrote:
>>>> (New thread due to very incorrect subject line and opening paragraph in
>>>> previous thread.)
>>>>
>>>> I still have not determined why DS101 will not turn on in my HP-1421A
>>>> time-base.? I can ground Q109's base through a resistor and force the lamp to
>>>> turn on.? I can place a 1K resistor in parallel with R137 and also force the
>>>> lamp to turn on; however, nothing else works. I thought that the neon might
>>>> have aged to the point where there isn't sufficient striking voltage for it
>>>> but since it will turn on with these methods, that doesn't seem to be case(?).
>>>>
>>>> Setting the unit up as described in the manual for voltage tests, I get the
>>>> following:
>>>>
>>>> -100V F(B): -99.9V
>>>>
>>>> Q109
>>>> Emitter: -9.35V
>>>> Base: -8.78V
>>>> Collector: -0.33V
>>>>
>>>> Q110
>>>> Emitter: -8.01V
>>>> Base: -8.11V
>>>> Collector: -3.7V
>>>>
>>>> Given those values, it would appear (at least to me) that the lamp should turn
>>>> on but it doesn't.
>>>>
>>>> As a test, I disconnected R136/DS101 (the yellow (4) wire) from the board and
>>>> connected a battery, resistor, and LED between GND and the collector of Q109.
>>>> This works just as it should (i.e. the LED turns on when the sweep is
>>>> triggered, turns off at the end of the sweep, and repeats that).
>>>>
>>>> Is it possible that Q109 is not able to conduct enough current to turn DS101
>>>> on but enough to make the LED work?? That seems unlikely but, at this point, I
>>>> don't have any other explanation.
>>>>
>>>> Any help with this is appreciated.
>>>>
>>>> Thanks,
>>>> Barry - N4BUQ
>>>>
>>>>
>>>
>>>
>>>
>>
>>
>>
>>
>
>
>
>
|
That's the action I see when using the LED circuit.? Yes, V105 illuminates as long as the RESET switch is pressed.? I don't have it in front of me, but I'm pretty sure mine is an 0803 prefix as well.
Thanks,
Barry - N4BUQ
My 1421A (serial 0803A03889), when I go to Single Sweep and press Reset switch S105, the Reset neon DS101 blinks and neon V105 illuminates as long as the switch is pressed.?
Barry, what happens when you go to Single Sweep and press Reset switch S105??
My schematic (and yours) shows the Collector of Q109 at +48V but your measurement shows -0.33V??
IIRC, when I had the front panel off for cleaning, I inspected those and I _think_ they were very close.? Although I don't know why, they used 1% resistors there.? Of course, that doesn't prevent them from drifting but I do think they were quite close to spec.
Thanks,
Barry - N4BUQ
----- Original Message -----
> From: "Peter Gottlieb" <hpnpilot@...>
> To: "HP-Agilent-Keysight-equipment" <[email protected]>
> Sent: Sunday, April 14, 2024 9:07:32 PM
> Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the Malfunctioning Time Base RESET Lamp in my
> HP-1421A.
> If you can lift Q109C then you could at least measure the sum of those two
> resistors.? But it would be nice to be able to measure the junction of them.
>
> On 4/14/2024 9:55 PM, n4buq via wrote:
>> I'll try grounding the collector of Q109.? Unfortunately, lifting one lead of
>> R136 isn't quick.? The front panel has to be removed to gain access to the
>> small assembly that holds DS101, R135, and R136.? It's too cramped to get to it
>> from the back side of the front of the chassis.
>>
>> Thanks,
>> Barry - N4BUQ
>>
>> ----- Original Message -----
>>> From: "Peter Gottlieb" <hpnpilot@...>
>>> To: "HP-Agilent-Keysight-equipment" <[email protected]>
>>> Sent: Sunday, April 14, 2024 8:10:33 PM
>>> Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the
>>> Malfunctioning Time Base RESET Lamp in my
>>> HP-1421A.
>>> Let's go real simple.? You report the collector of Q109 is at essentially
>>> ground, right?
>>>
>>> So if you ground it, and ASSUMING R135 AND R136 HAVEN'T DRIFTED, the neon should
>>> see 86.9 volts, which should light it.
>>>
>>> Neons when new fire somewhere in the 65 volt range but when old can easily drift
>>> upwards, even higher than that voltage.? And resistors can and do drift out of
>>> tolerance.
>>>
>>> Check R135 and R136 values.? Then ground Q109 collector and measure the junction
>>> of R135 and R136 voltage.? If you see near 86.9 volts your neon is old and has
>>> too high a firing voltage.
>>>
>>> Quick and dirty, try lifting one lead of R136 and see if the neon lights then.
>>>
>>> Peter
>>>
>>>
>>> On 4/14/2024 8:59 PM, n4buq via wrote:
>>>> (New thread due to very incorrect subject line and opening paragraph in
>>>> previous thread.)
>>>>
>>>> I still have not determined why DS101 will not turn on in my HP-1421A
>>>> time-base.? I can ground Q109's base through a resistor and force the lamp to
>>>> turn on.? I can place a 1K resistor in parallel with R137 and also force the
>>>> lamp to turn on; however, nothing else works. I thought that the neon might
>>>> have aged to the point where there isn't sufficient striking voltage for it
>>>> but since it will turn on with these methods, that doesn't seem to be case(?).
>>>>
>>>> Setting the unit up as described in the manual for voltage tests, I get the
>>>> following:
>>>>
>>>> -100V F(B): -99.9V
>>>>
>>>> Q109
>>>> Emitter: -9.35V
>>>> Base: -8.78V
>>>> Collector: -0.33V
>>>>
>>>> Q110
>>>> Emitter: -8.01V
>>>> Base: -8.11V
>>>> Collector: -3.7V
>>>>
>>>> Given those values, it would appear (at least to me) that the lamp should turn
>>>> on but it doesn't.
>>>>
>>>> As a test, I disconnected R136/DS101 (the yellow (4) wire) from the board and
>>>> connected a battery, resistor, and LED between GND and the collector of Q109.
>>>> This works just as it should (i.e. the LED turns on when the sweep is
>>>> triggered, turns off at the end of the sweep, and repeats that).
>>>>
>>>> Is it possible that Q109 is not able to conduct enough current to turn DS101
>>>> on but enough to make the LED work?? That seems unlikely but, at this point, I
>>>> don't have any other explanation.
>>>>
>>>> Any help with this is appreciated.
>>>>
>>>> Thanks,
>>>> Barry - N4BUQ
>>>>
>>>>
>>>
>>>
>>>
>>
>>
>>
>>
>
>
>
>
|
Barry, using either a very slow sweep speed (so there¡¯s time to watch the voltages change) or Single Sweep mode.?
Q109
Collector +65V before sweep begins, changes to -9V during sweep, then returns to +65V Emitter -9.39V changes to -9.09V and returns Base -11.6V changes to -8.5V and return
DS101 illuminates during sweep (regardless of length of sweep) and only during sweep. V105 illuminates only while S105 is pressed.?
If S105 is pressed and held, the sweep DOES NOT repeat. During the sweep, DS101 illuminates. When the sweep ends, DS101 extinguishes, whether S105 is held closed or not. S105 must be cycled OFF-ON to sweep again.?
Jeremy,
Neither NORMAL or SINGLE will cause the lamp to light but the LED lights properly in either mode.
The voltage at Q109's collector is what's puzzling me.? When I first turn it on, the voltage is somewhere close to the value on the schematic (I don't recall the exact voltage); however, after a few seconds, the voltage drops significantly to somewhere close to what I listed and if I recall, it continues to slowly drift towards zero over a period of 20 or 30 seconds.? I'm not sure what that voltage will settle to if I turn it on in SINGLE mode and no triggering event occurs.
I know that neon lamps do not need the firing voltage maintained in order to keep the lamp on but 52V seems quite low and that doesn't take into consideration how much voltage R135 drops so that would be just a bit less than 52V across the lamp.
It would be interesting to know what you see for the voltage at Q109's collector in your 1421A.
Thanks again, Barry - N4BUQ
Barry, what happens when you go to Single Sweep and press Reset switch S105??
My schematic (and yours) shows the Collector of Q109 at +48V but your measurement shows -0.33V??
IIRC, when I had the front panel off for cleaning, I inspected those and I _think_ they were very close.? Although I don't know why, they used 1% resistors there.? Of course, that doesn't prevent them from drifting but I do think they were quite close to spec.
Thanks,
Barry - N4BUQ
----- Original Message -----
> From: "Peter Gottlieb" <hpnpilot@...>
> To: "HP-Agilent-Keysight-equipment" <[email protected]>
> Sent: Sunday, April 14, 2024 9:07:32 PM
> Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the Malfunctioning Time Base RESET Lamp in my
> HP-1421A.
> If you can lift Q109C then you could at least measure the sum of those two
> resistors.? But it would be nice to be able to measure the junction of them.
>
> On 4/14/2024 9:55 PM, n4buq via wrote:
>> I'll try grounding the collector of Q109.? Unfortunately, lifting one lead of
>> R136 isn't quick.? The front panel has to be removed to gain access to the
>> small assembly that holds DS101, R135, and R136.? It's too cramped to get to it
>> from the back side of the front of the chassis.
>>
>> Thanks,
>> Barry - N4BUQ
>>
>> ----- Original Message -----
>>> From: "Peter Gottlieb" <hpnpilot@...>
>>> To: "HP-Agilent-Keysight-equipment" <[email protected]>
>>> Sent: Sunday, April 14, 2024 8:10:33 PM
>>> Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the
>>> Malfunctioning Time Base RESET Lamp in my
>>> HP-1421A.
>>> Let's go real simple.? You report the collector of Q109 is at essentially
>>> ground, right?
>>>
>>> So if you ground it, and ASSUMING R135 AND R136 HAVEN'T DRIFTED, the neon should
>>> see 86.9 volts, which should light it.
>>>
>>> Neons when new fire somewhere in the 65 volt range but when old can easily drift
>>> upwards, even higher than that voltage.? And resistors can and do drift out of
>>> tolerance.
>>>
>>> Check R135 and R136 values.? Then ground Q109 collector and measure the junction
>>> of R135 and R136 voltage.? If you see near 86.9 volts your neon is old and has
>>> too high a firing voltage.
>>>
>>> Quick and dirty, try lifting one lead of R136 and see if the neon lights then.
>>>
>>> Peter
>>>
>>>
>>> On 4/14/2024 8:59 PM, n4buq via wrote:
>>>> (New thread due to very incorrect subject line and opening paragraph in
>>>> previous thread.)
>>>>
>>>> I still have not determined why DS101 will not turn on in my HP-1421A
>>>> time-base.? I can ground Q109's base through a resistor and force the lamp to
>>>> turn on.? I can place a 1K resistor in parallel with R137 and also force the
>>>> lamp to turn on; however, nothing else works. I thought that the neon might
>>>> have aged to the point where there isn't sufficient striking voltage for it
>>>> but since it will turn on with these methods, that doesn't seem to be case(?).
>>>>
>>>> Setting the unit up as described in the manual for voltage tests, I get the
>>>> following:
>>>>
>>>> -100V F(B): -99.9V
>>>>
>>>> Q109
>>>> Emitter: -9.35V
>>>> Base: -8.78V
>>>> Collector: -0.33V
>>>>
>>>> Q110
>>>> Emitter: -8.01V
>>>> Base: -8.11V
>>>> Collector: -3.7V
>>>>
>>>> Given those values, it would appear (at least to me) that the lamp should turn
>>>> on but it doesn't.
>>>>
>>>> As a test, I disconnected R136/DS101 (the yellow (4) wire) from the board and
>>>> connected a battery, resistor, and LED between GND and the collector of Q109.
>>>> This works just as it should (i.e. the LED turns on when the sweep is
>>>> triggered, turns off at the end of the sweep, and repeats that).
>>>>
>>>> Is it possible that Q109 is not able to conduct enough current to turn DS101
>>>> on but enough to make the LED work?? That seems unlikely but, at this point, I
>>>> don't have any other explanation.
>>>>
>>>> Any help with this is appreciated.
>>>>
>>>> Thanks,
>>>> Barry - N4BUQ
>>>>
>>>>
>>>
>>>
>>>
>>
>>
>>
>>
>
>
>
>
|
I need to double-check but I don't think that's exactly how mine is working (or, more properly, _not_ working).
In SINGLE mode and using an external trigger and the LED circuit, pressing RESET causes the LED to illuminate and it stays illuminated.? If I then trigger the sweep via the EXTERNAL input, the LED stays illuminated until the sweep finishes, at which point, it is extinguished and stays extinguished until RESET is pressed.? That process is slightly easier to follow at a slow sweep speed.? If I switch to NORMAL mode, the LED flashes in time with the sweep start and finish but it's a bit more difficult to tell exactly when it comes on and when it goes off.
My DMM isn't the best for checking those voltage changes due to it's relatively slow speed at which changed voltages appear.? I'll switch to watching that on another scope to get a clearer picture of those changes.
Thanks for checking that and the detailed voltage change points!
Barry - N4BUQ
From: "Jeremy Nichols" <jn6wfo@...>
To: "HP-Agilent-Keysight-equipment" <[email protected]>
Sent: Sunday, April 14, 2024 10:24:00 PM
Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the Malfunctioning Time Base RESET Lamp in my HP-1421A.
Barry, using either a very slow sweep speed (so there¡¯s time to watch the voltages change) or Single Sweep mode.?
Q109
Collector +65V before sweep begins, changes to -9V during sweep, then returns to +65V Emitter -9.39V changes to -9.09V and returns Base -11.6V changes to -8.5V and return
DS101 illuminates during sweep (regardless of length of sweep) and only during sweep. V105 illuminates only while S105 is pressed.?
If S105 is pressed and held, the sweep DOES NOT repeat. During the sweep, DS101 illuminates. When the sweep ends, DS101 extinguishes, whether S105 is held closed or not. S105 must be cycled OFF-ON to sweep again.?
Jeremy, Neither NORMAL or SINGLE will cause the lamp to light but the LED lights properly in either mode. The voltage at Q109's collector is what's puzzling me.? When I first turn it on, the voltage is somewhere close to the value on the schematic (I don't recall the exact voltage); however, after a few seconds, the voltage drops significantly to somewhere close to what I listed and if I recall, it continues to slowly drift towards zero over a period of 20 or 30 seconds.? I'm not sure what that voltage will settle to if I turn it on in SINGLE mode and no triggering event occurs. I know that neon lamps do not need the firing voltage maintained in order to keep the lamp on but 52V seems quite low and that doesn't take into consideration how much voltage R135 drops so that would be just a bit less than 52V across the lamp. It would be interesting to know what you see for the voltage at Q109's collector in your 1421A. Thanks again, Barry - N4BUQ Barry, what happens when you go to Single Sweep and press Reset switch S105??
My schematic (and yours) shows the Collector of Q109 at +48V but your measurement shows -0.33V??
IIRC, when I had the front panel off for cleaning, I inspected those and I _think_ they were very close.? Although I don't know why, they used 1% resistors there.? Of course, that doesn't prevent them from drifting but I do think they were quite close to spec.
Thanks,
Barry - N4BUQ
----- Original Message -----
> From: "Peter Gottlieb" <hpnpilot@...>
> To: "HP-Agilent-Keysight-equipment" <[email protected]>
> Sent: Sunday, April 14, 2024 9:07:32 PM
> Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the Malfunctioning Time Base RESET Lamp in my
> HP-1421A.
> If you can lift Q109C then you could at least measure the sum of those two
> resistors.? But it would be nice to be able to measure the junction of them.
>
> On 4/14/2024 9:55 PM, n4buq via wrote:
>> I'll try grounding the collector of Q109.? Unfortunately, lifting one lead of
>> R136 isn't quick.? The front panel has to be removed to gain access to the
>> small assembly that holds DS101, R135, and R136.? It's too cramped to get to it
>> from the back side of the front of the chassis.
>>
>> Thanks,
>> Barry - N4BUQ
>>
>> ----- Original Message -----
>>> From: "Peter Gottlieb" <hpnpilot@...>
>>> To: "HP-Agilent-Keysight-equipment" <[email protected]>
>>> Sent: Sunday, April 14, 2024 8:10:33 PM
>>> Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the
>>> Malfunctioning Time Base RESET Lamp in my
>>> HP-1421A.
>>> Let's go real simple.? You report the collector of Q109 is at essentially
>>> ground, right?
>>>
>>> So if you ground it, and ASSUMING R135 AND R136 HAVEN'T DRIFTED, the neon should
>>> see 86.9 volts, which should light it.
>>>
>>> Neons when new fire somewhere in the 65 volt range but when old can easily drift
>>> upwards, even higher than that voltage.? And resistors can and do drift out of
>>> tolerance.
>>>
>>> Check R135 and R136 values.? Then ground Q109 collector and measure the junction
>>> of R135 and R136 voltage.? If you see near 86.9 volts your neon is old and has
>>> too high a firing voltage.
>>>
>>> Quick and dirty, try lifting one lead of R136 and see if the neon lights then.
>>>
>>> Peter
>>>
>>>
>>> On 4/14/2024 8:59 PM, n4buq via wrote:
>>>> (New thread due to very incorrect subject line and opening paragraph in
>>>> previous thread.)
>>>>
>>>> I still have not determined why DS101 will not turn on in my HP-1421A
>>>> time-base.? I can ground Q109's base through a resistor and force the lamp to
>>>> turn on.? I can place a 1K resistor in parallel with R137 and also force the
>>>> lamp to turn on; however, nothing else works. I thought that the neon might
>>>> have aged to the point where there isn't sufficient striking voltage for it
>>>> but since it will turn on with these methods, that doesn't seem to be case(?).
>>>>
>>>> Setting the unit up as described in the manual for voltage tests, I get the
>>>> following:
>>>>
>>>> -100V F(B): -99.9V
>>>>
>>>> Q109
>>>> Emitter: -9.35V
>>>> Base: -8.78V
>>>> Collector: -0.33V
>>>>
>>>> Q110
>>>> Emitter: -8.01V
>>>> Base: -8.11V
>>>> Collector: -3.7V
>>>>
>>>> Given those values, it would appear (at least to me) that the lamp should turn
>>>> on but it doesn't.
>>>>
>>>> As a test, I disconnected R136/DS101 (the yellow (4) wire) from the board and
>>>> connected a battery, resistor, and LED between GND and the collector of Q109.
>>>> This works just as it should (i.e. the LED turns on when the sweep is
>>>> triggered, turns off at the end of the sweep, and repeats that).
>>>>
>>>> Is it possible that Q109 is not able to conduct enough current to turn DS101
>>>> on but enough to make the LED work?? That seems unlikely but, at this point, I
>>>> don't have any other explanation.
>>>>
>>>> Any help with this is appreciated.
>>>>
>>>> Thanks,
>>>> Barry - N4BUQ
>>>>
>>>>
>>>
>>>
>>>
>>
>>
>>
>>
>
>
>
>
|
A very slow sweep speed (several seconds to sweep across the CRT) will give your DVM time to display the changing voltages at Q109.?
I need to double-check but I don't think that's exactly how mine is working (or, more properly, _not_ working).
In SINGLE mode and using an external trigger and the LED circuit, pressing RESET causes the LED to illuminate and it stays illuminated.? If I then trigger the sweep via the EXTERNAL input, the LED stays illuminated until the sweep finishes, at which point, it is extinguished and stays extinguished until RESET is pressed.? That process is slightly easier to follow at a slow sweep speed.? If I switch to NORMAL mode, the LED flashes in time with the sweep start and finish but it's a bit more difficult to tell exactly when it comes on and when it goes off.
My DMM isn't the best for checking those voltage changes due to it's relatively slow speed at which changed voltages appear.? I'll switch to watching that on another scope to get a clearer picture of those changes.
Thanks for checking that and the detailed voltage change points!
Barry - N4BUQ
From: "Jeremy Nichols" <jn6wfo@...>
To: "HP-Agilent-Keysight-equipment" <[email protected]>
Sent: Sunday, April 14, 2024 10:24:00 PM
Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the Malfunctioning Time Base RESET Lamp in my HP-1421A.
Barry, using either a very slow sweep speed (so there¡¯s time to watch the voltages change) or Single Sweep mode.?
Q109
Collector +65V before sweep begins, changes to -9V during sweep, then returns to +65V Emitter -9.39V changes to -9.09V and returns Base -11.6V changes to -8.5V and return
DS101 illuminates during sweep (regardless of length of sweep) and only during sweep. V105 illuminates only while S105 is pressed.?
If S105 is pressed and held, the sweep DOES NOT repeat. During the sweep, DS101 illuminates. When the sweep ends, DS101 extinguishes, whether S105 is held closed or not. S105 must be cycled OFF-ON to sweep again.?
Jeremy, Neither NORMAL or SINGLE will cause the lamp to light but the LED lights properly in either mode. The voltage at Q109's collector is what's puzzling me.? When I first turn it on, the voltage is somewhere close to the value on the schematic (I don't recall the exact voltage); however, after a few seconds, the voltage drops significantly to somewhere close to what I listed and if I recall, it continues to slowly drift towards zero over a period of 20 or 30 seconds.? I'm not sure what that voltage will settle to if I turn it on in SINGLE mode and no triggering event occurs. I know that neon lamps do not need the firing voltage maintained in order to keep the lamp on but 52V seems quite low and that doesn't take into consideration how much voltage R135 drops so that would be just a bit less than 52V across the lamp. It would be interesting to know what you see for the voltage at Q109's collector in your 1421A. Thanks again, Barry - N4BUQ Barry, what happens when you go to Single Sweep and press Reset switch S105??
My schematic (and yours) shows the Collector of Q109 at +48V but your measurement shows -0.33V??
IIRC, when I had the front panel off for cleaning, I inspected those and I _think_ they were very close.? Although I don't know why, they used 1% resistors there.? Of course, that doesn't prevent them from drifting but I do think they were quite close to spec.
Thanks,
Barry - N4BUQ
----- Original Message -----
> From: "Peter Gottlieb" <hpnpilot@...>
> To: "HP-Agilent-Keysight-equipment" <[email protected]>
> Sent: Sunday, April 14, 2024 9:07:32 PM
> Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the Malfunctioning Time Base RESET Lamp in my
> HP-1421A.
> If you can lift Q109C then you could at least measure the sum of those two
> resistors.? But it would be nice to be able to measure the junction of them.
>
> On 4/14/2024 9:55 PM, n4buq via wrote:
>> I'll try grounding the collector of Q109.? Unfortunately, lifting one lead of
>> R136 isn't quick.? The front panel has to be removed to gain access to the
>> small assembly that holds DS101, R135, and R136.? It's too cramped to get to it
>> from the back side of the front of the chassis.
>>
>> Thanks,
>> Barry - N4BUQ
>>
>> ----- Original Message -----
>>> From: "Peter Gottlieb" <hpnpilot@...>
>>> To: "HP-Agilent-Keysight-equipment" <[email protected]>
>>> Sent: Sunday, April 14, 2024 8:10:33 PM
>>> Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the
>>> Malfunctioning Time Base RESET Lamp in my
>>> HP-1421A.
>>> Let's go real simple.? You report the collector of Q109 is at essentially
>>> ground, right?
>>>
>>> So if you ground it, and ASSUMING R135 AND R136 HAVEN'T DRIFTED, the neon should
>>> see 86.9 volts, which should light it.
>>>
>>> Neons when new fire somewhere in the 65 volt range but when old can easily drift
>>> upwards, even higher than that voltage.? And resistors can and do drift out of
>>> tolerance.
>>>
>>> Check R135 and R136 values.? Then ground Q109 collector and measure the junction
>>> of R135 and R136 voltage.? If you see near 86.9 volts your neon is old and has
>>> too high a firing voltage.
>>>
>>> Quick and dirty, try lifting one lead of R136 and see if the neon lights then.
>>>
>>> Peter
>>>
>>>
>>> On 4/14/2024 8:59 PM, n4buq via wrote:
>>>> (New thread due to very incorrect subject line and opening paragraph in
>>>> previous thread.)
>>>>
>>>> I still have not determined why DS101 will not turn on in my HP-1421A
>>>> time-base.? I can ground Q109's base through a resistor and force the lamp to
>>>> turn on.? I can place a 1K resistor in parallel with R137 and also force the
>>>> lamp to turn on; however, nothing else works. I thought that the neon might
>>>> have aged to the point where there isn't sufficient striking voltage for it
>>>> but since it will turn on with these methods, that doesn't seem to be case(?).
>>>>
>>>> Setting the unit up as described in the manual for voltage tests, I get the
>>>> following:
>>>>
>>>> -100V F(B): -99.9V
>>>>
>>>> Q109
>>>> Emitter: -9.35V
>>>> Base: -8.78V
>>>> Collector: -0.33V
>>>>
>>>> Q110
>>>> Emitter: -8.01V
>>>> Base: -8.11V
>>>> Collector: -3.7V
>>>>
>>>> Given those values, it would appear (at least to me) that the lamp should turn
>>>> on but it doesn't.
>>>>
>>>> As a test, I disconnected R136/DS101 (the yellow (4) wire) from the board and
>>>> connected a battery, resistor, and LED between GND and the collector of Q109.
>>>> This works just as it should (i.e. the LED turns on when the sweep is
>>>> triggered, turns off at the end of the sweep, and repeats that).
>>>>
>>>> Is it possible that Q109 is not able to conduct enough current to turn DS101
>>>> on but enough to make the LED work?? That seems unlikely but, at this point, I
>>>> don't have any other explanation.
>>>>
>>>> Any help with this is appreciated.
>>>>
>>>> Thanks,
>>>> Barry - N4BUQ
>>>>
>>>>
>>>
>>>
>>>
>>
>>
>>
>>
>
>
>
>
|
I'll test again tomorrow and see what I can find out. Thanks,
Barry - N4BUQ
From: "Jeremy Nichols" <jn6wfo@...>
To: "HP-Agilent-Keysight-equipment" <[email protected]>
Sent: Sunday, April 14, 2024 11:07:04 PM
Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the Malfunctioning Time Base RESET Lamp in my HP-1421A.
A very slow sweep speed (several seconds to sweep across the CRT) will give your DVM time to display the changing voltages at Q109.?
I need to double-check but I don't think that's exactly how mine is working (or, more properly, _not_ working). In SINGLE mode and using an external trigger and the LED circuit, pressing RESET causes the LED to illuminate and it stays illuminated.? If I then trigger the sweep via the EXTERNAL input, the LED stays illuminated until the sweep finishes, at which point, it is extinguished and stays extinguished until RESET is pressed.? That process is slightly easier to follow at a slow sweep speed.? If I switch to NORMAL mode, the LED flashes in time with the sweep start and finish but it's a bit more difficult to tell exactly when it comes on and when it goes off. My DMM isn't the best for checking those voltage changes due to it's relatively slow speed at which changed voltages appear.? I'll switch to watching that on another scope to get a clearer picture of those changes. Thanks for checking that and the detailed voltage change points! Barry - N4BUQ
From: "Jeremy Nichols" <jn6wfo@...>
To: "HP-Agilent-Keysight-equipment" <[email protected]>
Sent: Sunday, April 14, 2024 10:24:00 PM
Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the Malfunctioning Time Base RESET Lamp in my HP-1421A.
Barry, using either a very slow sweep speed (so there¡¯s time to watch the voltages change) or Single Sweep mode.?
Q109
Collector +65V before sweep begins, changes to -9V during sweep, then returns to +65V Emitter -9.39V changes to -9.09V and returns Base -11.6V changes to -8.5V and return
DS101 illuminates during sweep (regardless of length of sweep) and only during sweep. V105 illuminates only while S105 is pressed.?
If S105 is pressed and held, the sweep DOES NOT repeat. During the sweep, DS101 illuminates. When the sweep ends, DS101 extinguishes, whether S105 is held closed or not. S105 must be cycled OFF-ON to sweep again.?
Jeremy, Neither NORMAL or SINGLE will cause the lamp to light but the LED lights properly in either mode. The voltage at Q109's collector is what's puzzling me.? When I first turn it on, the voltage is somewhere close to the value on the schematic (I don't recall the exact voltage); however, after a few seconds, the voltage drops significantly to somewhere close to what I listed and if I recall, it continues to slowly drift towards zero over a period of 20 or 30 seconds.? I'm not sure what that voltage will settle to if I turn it on in SINGLE mode and no triggering event occurs. I know that neon lamps do not need the firing voltage maintained in order to keep the lamp on but 52V seems quite low and that doesn't take into consideration how much voltage R135 drops so that would be just a bit less than 52V across the lamp. It would be interesting to know what you see for the voltage at Q109's collector in your 1421A. Thanks again, Barry - N4BUQ Barry, what happens when you go to Single Sweep and press Reset switch S105??
My schematic (and yours) shows the Collector of Q109 at +48V but your measurement shows -0.33V??
IIRC, when I had the front panel off for cleaning, I inspected those and I _think_ they were very close.? Although I don't know why, they used 1% resistors there.? Of course, that doesn't prevent them from drifting but I do think they were quite close to spec.
Thanks,
Barry - N4BUQ
----- Original Message -----
> From: "Peter Gottlieb" <hpnpilot@...>
> To: "HP-Agilent-Keysight-equipment" <[email protected]>
> Sent: Sunday, April 14, 2024 9:07:32 PM
> Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the Malfunctioning Time Base RESET Lamp in my
> HP-1421A.
> If you can lift Q109C then you could at least measure the sum of those two
> resistors.? But it would be nice to be able to measure the junction of them.
>
> On 4/14/2024 9:55 PM, n4buq via wrote:
>> I'll try grounding the collector of Q109.? Unfortunately, lifting one lead of
>> R136 isn't quick.? The front panel has to be removed to gain access to the
>> small assembly that holds DS101, R135, and R136.? It's too cramped to get to it
>> from the back side of the front of the chassis.
>>
>> Thanks,
>> Barry - N4BUQ
>>
>> ----- Original Message -----
>>> From: "Peter Gottlieb" <hpnpilot@...>
>>> To: "HP-Agilent-Keysight-equipment" <[email protected]>
>>> Sent: Sunday, April 14, 2024 8:10:33 PM
>>> Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the
>>> Malfunctioning Time Base RESET Lamp in my
>>> HP-1421A.
>>> Let's go real simple.? You report the collector of Q109 is at essentially
>>> ground, right?
>>>
>>> So if you ground it, and ASSUMING R135 AND R136 HAVEN'T DRIFTED, the neon should
>>> see 86.9 volts, which should light it.
>>>
>>> Neons when new fire somewhere in the 65 volt range but when old can easily drift
>>> upwards, even higher than that voltage.? And resistors can and do drift out of
>>> tolerance.
>>>
>>> Check R135 and R136 values.? Then ground Q109 collector and measure the junction
>>> of R135 and R136 voltage.? If you see near 86.9 volts your neon is old and has
>>> too high a firing voltage.
>>>
>>> Quick and dirty, try lifting one lead of R136 and see if the neon lights then.
>>>
>>> Peter
>>>
>>>
>>> On 4/14/2024 8:59 PM, n4buq via wrote:
>>>> (New thread due to very incorrect subject line and opening paragraph in
>>>> previous thread.)
>>>>
>>>> I still have not determined why DS101 will not turn on in my HP-1421A
>>>> time-base.? I can ground Q109's base through a resistor and force the lamp to
>>>> turn on.? I can place a 1K resistor in parallel with R137 and also force the
>>>> lamp to turn on; however, nothing else works. I thought that the neon might
>>>> have aged to the point where there isn't sufficient striking voltage for it
>>>> but since it will turn on with these methods, that doesn't seem to be case(?).
>>>>
>>>> Setting the unit up as described in the manual for voltage tests, I get the
>>>> following:
>>>>
>>>> -100V F(B): -99.9V
>>>>
>>>> Q109
>>>> Emitter: -9.35V
>>>> Base: -8.78V
>>>> Collector: -0.33V
>>>>
>>>> Q110
>>>> Emitter: -8.01V
>>>> Base: -8.11V
>>>> Collector: -3.7V
>>>>
>>>> Given those values, it would appear (at least to me) that the lamp should turn
>>>> on but it doesn't.
>>>>
>>>> As a test, I disconnected R136/DS101 (the yellow (4) wire) from the board and
>>>> connected a battery, resistor, and LED between GND and the collector of Q109.
>>>> This works just as it should (i.e. the LED turns on when the sweep is
>>>> triggered, turns off at the end of the sweep, and repeats that).
>>>>
>>>> Is it possible that Q109 is not able to conduct enough current to turn DS101
>>>> on but enough to make the LED work?? That seems unlikely but, at this point, I
>>>> don't have any other explanation.
>>>>
>>>> Any help with this is appreciated.
>>>>
>>>> Thanks,
>>>> Barry - N4BUQ
>>>>
>>>>
>>>
>>>
>>>
>>
>>
>>
>>
>
>
>
>
|
Barry, it sounds like Q109 is leaky to cause the collector voltage to slowly drop from +65 to almost zero. If something was causing Q109 to be turned on, the neon should illuminate, because Q109 would become a closed switch, allowing current to flow from +100V through the neon and through Q109 and through R139 to ground.?
I'll test again tomorrow and see what I can find out. Thanks,
Barry - N4BUQ
From: "Jeremy Nichols" <jn6wfo@...>
To: "HP-Agilent-Keysight-equipment" <[email protected]>
Sent: Sunday, April 14, 2024 11:07:04 PM
Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the Malfunctioning Time Base RESET Lamp in my HP-1421A.
A very slow sweep speed (several seconds to sweep across the CRT) will give your DVM time to display the changing voltages at Q109.?
I need to double-check but I don't think that's exactly how mine is working (or, more properly, _not_ working). In SINGLE mode and using an external trigger and the LED circuit, pressing RESET causes the LED to illuminate and it stays illuminated.? If I then trigger the sweep via the EXTERNAL input, the LED stays illuminated until the sweep finishes, at which point, it is extinguished and stays extinguished until RESET is pressed.? That process is slightly easier to follow at a slow sweep speed.? If I switch to NORMAL mode, the LED flashes in time with the sweep start and finish but it's a bit more difficult to tell exactly when it comes on and when it goes off. My DMM isn't the best for checking those voltage changes due to it's relatively slow speed at which changed voltages appear.? I'll switch to watching that on another scope to get a clearer picture of those changes. Thanks for checking that and the detailed voltage change points! Barry - N4BUQ
From: "Jeremy Nichols" <jn6wfo@...>
To: "HP-Agilent-Keysight-equipment" <[email protected]>
Sent: Sunday, April 14, 2024 10:24:00 PM
Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the Malfunctioning Time Base RESET Lamp in my HP-1421A.
Barry, using either a very slow sweep speed (so there¡¯s time to watch the voltages change) or Single Sweep mode.?
Q109
Collector +65V before sweep begins, changes to -9V during sweep, then returns to +65V Emitter -9.39V changes to -9.09V and returns Base -11.6V changes to -8.5V and return
DS101 illuminates during sweep (regardless of length of sweep) and only during sweep. V105 illuminates only while S105 is pressed.?
If S105 is pressed and held, the sweep DOES NOT repeat. During the sweep, DS101 illuminates. When the sweep ends, DS101 extinguishes, whether S105 is held closed or not. S105 must be cycled OFF-ON to sweep again.?
Jeremy, Neither NORMAL or SINGLE will cause the lamp to light but the LED lights properly in either mode. The voltage at Q109's collector is what's puzzling me.? When I first turn it on, the voltage is somewhere close to the value on the schematic (I don't recall the exact voltage); however, after a few seconds, the voltage drops significantly to somewhere close to what I listed and if I recall, it continues to slowly drift towards zero over a period of 20 or 30 seconds.? I'm not sure what that voltage will settle to if I turn it on in SINGLE mode and no triggering event occurs. I know that neon lamps do not need the firing voltage maintained in order to keep the lamp on but 52V seems quite low and that doesn't take into consideration how much voltage R135 drops so that would be just a bit less than 52V across the lamp. It would be interesting to know what you see for the voltage at Q109's collector in your 1421A. Thanks again, Barry - N4BUQ Barry, what happens when you go to Single Sweep and press Reset switch S105??
My schematic (and yours) shows the Collector of Q109 at +48V but your measurement shows -0.33V??
IIRC, when I had the front panel off for cleaning, I inspected those and I _think_ they were very close.? Although I don't know why, they used 1% resistors there.? Of course, that doesn't prevent them from drifting but I do think they were quite close to spec.
Thanks,
Barry - N4BUQ
----- Original Message -----
> From: "Peter Gottlieb" <hpnpilot@...>
> To: "HP-Agilent-Keysight-equipment" <[email protected]>
> Sent: Sunday, April 14, 2024 9:07:32 PM
> Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the Malfunctioning Time Base RESET Lamp in my
> HP-1421A.
> If you can lift Q109C then you could at least measure the sum of those two
> resistors.? But it would be nice to be able to measure the junction of them.
>
> On 4/14/2024 9:55 PM, n4buq via wrote:
>> I'll try grounding the collector of Q109.? Unfortunately, lifting one lead of
>> R136 isn't quick.? The front panel has to be removed to gain access to the
>> small assembly that holds DS101, R135, and R136.? It's too cramped to get to it
>> from the back side of the front of the chassis.
>>
>> Thanks,
>> Barry - N4BUQ
>>
>> ----- Original Message -----
>>> From: "Peter Gottlieb" <hpnpilot@...>
>>> To: "HP-Agilent-Keysight-equipment" <[email protected]>
>>> Sent: Sunday, April 14, 2024 8:10:33 PM
>>> Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the
>>> Malfunctioning Time Base RESET Lamp in my
>>> HP-1421A.
>>> Let's go real simple.? You report the collector of Q109 is at essentially
>>> ground, right?
>>>
>>> So if you ground it, and ASSUMING R135 AND R136 HAVEN'T DRIFTED, the neon should
>>> see 86.9 volts, which should light it.
>>>
>>> Neons when new fire somewhere in the 65 volt range but when old can easily drift
>>> upwards, even higher than that voltage.? And resistors can and do drift out of
>>> tolerance.
>>>
>>> Check R135 and R136 values.? Then ground Q109 collector and measure the junction
>>> of R135 and R136 voltage.? If you see near 86.9 volts your neon is old and has
>>> too high a firing voltage.
>>>
>>> Quick and dirty, try lifting one lead of R136 and see if the neon lights then.
>>>
>>> Peter
>>>
>>>
>>> On 4/14/2024 8:59 PM, n4buq via wrote:
>>>> (New thread due to very incorrect subject line and opening paragraph in
>>>> previous thread.)
>>>>
>>>> I still have not determined why DS101 will not turn on in my HP-1421A
>>>> time-base.? I can ground Q109's base through a resistor and force the lamp to
>>>> turn on.? I can place a 1K resistor in parallel with R137 and also force the
>>>> lamp to turn on; however, nothing else works. I thought that the neon might
>>>> have aged to the point where there isn't sufficient striking voltage for it
>>>> but since it will turn on with these methods, that doesn't seem to be case(?).
>>>>
>>>> Setting the unit up as described in the manual for voltage tests, I get the
>>>> following:
>>>>
>>>> -100V F(B): -99.9V
>>>>
>>>> Q109
>>>> Emitter: -9.35V
>>>> Base: -8.78V
>>>> Collector: -0.33V
>>>>
>>>> Q110
>>>> Emitter: -8.01V
>>>> Base: -8.11V
>>>> Collector: -3.7V
>>>>
>>>> Given those values, it would appear (at least to me) that the lamp should turn
>>>> on but it doesn't.
>>>>
>>>> As a test, I disconnected R136/DS101 (the yellow (4) wire) from the board and
>>>> connected a battery, resistor, and LED between GND and the collector of Q109.
>>>> This works just as it should (i.e. the LED turns on when the sweep is
>>>> triggered, turns off at the end of the sweep, and repeats that).
>>>>
>>>> Is it possible that Q109 is not able to conduct enough current to turn DS101
>>>> on but enough to make the LED work?? That seems unlikely but, at this point, I
>>>> don't have any other explanation.
>>>>
>>>> Any help with this is appreciated.
>>>>
>>>> Thanks,
>>>> Barry - N4BUQ
>>>>
>>>>
>>>
>>>
>>>
>>
>>
>>
>>
>
>
>
>
|
Q109¡¯s collector voltage is set by R135 and R136 in series with the +100V supply (assuming a non-conducting DS101 has near-infinite DC resistance) and R137 and Q109¡¯s DC resistance (collector to emitter) in parallel to the -9.4V point set by R138 and R139 that are connected between the -12.6V supply and ground.?
If you are seeing the collector voltage start at ¡°normal¡± (+65V in my ¡®scope) and slowly drop towards zero, then something is allowing current from Q109¡¯s collector. It has to be a very small current or DS101 would illuminate.?
On Sun, Apr 14, 2024 at 10:25?PM Jeremy Nichols via <jn6wfo= [email protected]> wrote: Barry, it sounds like Q109 is leaky to cause the collector voltage to slowly drop from +65 to almost zero. If something was causing Q109 to be turned on, the neon should illuminate, because Q109 would become a closed switch, allowing current to flow from +100V through the neon and through Q109 and through R139 to ground.?
I'll test again tomorrow and see what I can find out. Thanks,
Barry - N4BUQ
From: "Jeremy Nichols" <jn6wfo@...>
To: "HP-Agilent-Keysight-equipment" <[email protected]>
Sent: Sunday, April 14, 2024 11:07:04 PM
Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the Malfunctioning Time Base RESET Lamp in my HP-1421A.
A very slow sweep speed (several seconds to sweep across the CRT) will give your DVM time to display the changing voltages at Q109.?
I need to double-check but I don't think that's exactly how mine is working (or, more properly, _not_ working). In SINGLE mode and using an external trigger and the LED circuit, pressing RESET causes the LED to illuminate and it stays illuminated.? If I then trigger the sweep via the EXTERNAL input, the LED stays illuminated until the sweep finishes, at which point, it is extinguished and stays extinguished until RESET is pressed.? That process is slightly easier to follow at a slow sweep speed.? If I switch to NORMAL mode, the LED flashes in time with the sweep start and finish but it's a bit more difficult to tell exactly when it comes on and when it goes off. My DMM isn't the best for checking those voltage changes due to it's relatively slow speed at which changed voltages appear.? I'll switch to watching that on another scope to get a clearer picture of those changes. Thanks for checking that and the detailed voltage change points! Barry - N4BUQ
From: "Jeremy Nichols" <jn6wfo@...>
To: "HP-Agilent-Keysight-equipment" <[email protected]>
Sent: Sunday, April 14, 2024 10:24:00 PM
Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the Malfunctioning Time Base RESET Lamp in my HP-1421A.
Barry, using either a very slow sweep speed (so there¡¯s time to watch the voltages change) or Single Sweep mode.?
Q109
Collector +65V before sweep begins, changes to -9V during sweep, then returns to +65V Emitter -9.39V changes to -9.09V and returns Base -11.6V changes to -8.5V and return
DS101 illuminates during sweep (regardless of length of sweep) and only during sweep. V105 illuminates only while S105 is pressed.?
If S105 is pressed and held, the sweep DOES NOT repeat. During the sweep, DS101 illuminates. When the sweep ends, DS101 extinguishes, whether S105 is held closed or not. S105 must be cycled OFF-ON to sweep again.?
Jeremy, Neither NORMAL or SINGLE will cause the lamp to light but the LED lights properly in either mode. The voltage at Q109's collector is what's puzzling me.? When I first turn it on, the voltage is somewhere close to the value on the schematic (I don't recall the exact voltage); however, after a few seconds, the voltage drops significantly to somewhere close to what I listed and if I recall, it continues to slowly drift towards zero over a period of 20 or 30 seconds.? I'm not sure what that voltage will settle to if I turn it on in SINGLE mode and no triggering event occurs. I know that neon lamps do not need the firing voltage maintained in order to keep the lamp on but 52V seems quite low and that doesn't take into consideration how much voltage R135 drops so that would be just a bit less than 52V across the lamp. It would be interesting to know what you see for the voltage at Q109's collector in your 1421A. Thanks again, Barry - N4BUQ Barry, what happens when you go to Single Sweep and press Reset switch S105??
My schematic (and yours) shows the Collector of Q109 at +48V but your measurement shows -0.33V??
IIRC, when I had the front panel off for cleaning, I inspected those and I _think_ they were very close.? Although I don't know why, they used 1% resistors there.? Of course, that doesn't prevent them from drifting but I do think they were quite close to spec.
Thanks,
Barry - N4BUQ
----- Original Message -----
> From: "Peter Gottlieb" <hpnpilot@...>
> To: "HP-Agilent-Keysight-equipment" <[email protected]>
> Sent: Sunday, April 14, 2024 9:07:32 PM
> Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the Malfunctioning Time Base RESET Lamp in my
> HP-1421A.
> If you can lift Q109C then you could at least measure the sum of those two
> resistors.? But it would be nice to be able to measure the junction of them.
>
> On 4/14/2024 9:55 PM, n4buq via wrote:
>> I'll try grounding the collector of Q109.? Unfortunately, lifting one lead of
>> R136 isn't quick.? The front panel has to be removed to gain access to the
>> small assembly that holds DS101, R135, and R136.? It's too cramped to get to it
>> from the back side of the front of the chassis.
>>
>> Thanks,
>> Barry - N4BUQ
>>
>> ----- Original Message -----
>>> From: "Peter Gottlieb" <hpnpilot@...>
>>> To: "HP-Agilent-Keysight-equipment" <[email protected]>
>>> Sent: Sunday, April 14, 2024 8:10:33 PM
>>> Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the
>>> Malfunctioning Time Base RESET Lamp in my
>>> HP-1421A.
>>> Let's go real simple.? You report the collector of Q109 is at essentially
>>> ground, right?
>>>
>>> So if you ground it, and ASSUMING R135 AND R136 HAVEN'T DRIFTED, the neon should
>>> see 86.9 volts, which should light it.
>>>
>>> Neons when new fire somewhere in the 65 volt range but when old can easily drift
>>> upwards, even higher than that voltage.? And resistors can and do drift out of
>>> tolerance.
>>>
>>> Check R135 and R136 values.? Then ground Q109 collector and measure the junction
>>> of R135 and R136 voltage.? If you see near 86.9 volts your neon is old and has
>>> too high a firing voltage.
>>>
>>> Quick and dirty, try lifting one lead of R136 and see if the neon lights then.
>>>
>>> Peter
>>>
>>>
>>> On 4/14/2024 8:59 PM, n4buq via wrote:
>>>> (New thread due to very incorrect subject line and opening paragraph in
>>>> previous thread.)
>>>>
>>>> I still have not determined why DS101 will not turn on in my HP-1421A
>>>> time-base.? I can ground Q109's base through a resistor and force the lamp to
>>>> turn on.? I can place a 1K resistor in parallel with R137 and also force the
>>>> lamp to turn on; however, nothing else works. I thought that the neon might
>>>> have aged to the point where there isn't sufficient striking voltage for it
>>>> but since it will turn on with these methods, that doesn't seem to be case(?).
>>>>
>>>> Setting the unit up as described in the manual for voltage tests, I get the
>>>> following:
>>>>
>>>> -100V F(B): -99.9V
>>>>
>>>> Q109
>>>> Emitter: -9.35V
>>>> Base: -8.78V
>>>> Collector: -0.33V
>>>>
>>>> Q110
>>>> Emitter: -8.01V
>>>> Base: -8.11V
>>>> Collector: -3.7V
>>>>
>>>> Given those values, it would appear (at least to me) that the lamp should turn
>>>> on but it doesn't.
>>>>
>>>> As a test, I disconnected R136/DS101 (the yellow (4) wire) from the board and
>>>> connected a battery, resistor, and LED between GND and the collector of Q109.
>>>> This works just as it should (i.e. the LED turns on when the sweep is
>>>> triggered, turns off at the end of the sweep, and repeats that).
>>>>
>>>> Is it possible that Q109 is not able to conduct enough current to turn DS101
>>>> on but enough to make the LED work?? That seems unlikely but, at this point, I
>>>> don't have any other explanation.
>>>>
>>>> Any help with this is appreciated.
>>>>
>>>> Thanks,
>>>> Barry - N4BUQ
>>>>
>>>>
>>>
>>>
>>>
>>
>>
>>
>>
>
>
>
>
|
Jeremy,
I get very close to the exact same readings but the lamp doesn't illuminate.? I think that a 2N5551 is a suitable sub for Q109 (1854-0022).? Thinking that the existing Q109 isn't working, I tried placing the 2N5551 in parallel with it but still no luck.? I was presuming that if the existing Q109 isn't turning on as expected, the 2N5551 would turn on and close the circuit but that may be an invalid way of testing and I may need to remove Q109.? I was just trying to avoid removing Q109 if it was really working but something else is the problem.
BTW, I have some A9A neons.? I tried removing the existing DS101's connection to Q109's collector and connected the A9A with a 50k series resistor from Q109's collector to the +100V rail.? It still didn't work but 50k may have too high a value for that circuit.? I did try connecting the 50k and the A9A from +100V directly to GND and the bulb illuminated but rather weakly.? The additional circuitry with Q109 and the other resistors may have limited the current too much.? I plan to try that with a more suitable resistor somewhere around 20k and see what that shows.
Thanks, Barry - N4BUQ
Barry, using either a very slow sweep speed (so there¡¯s time to watch the voltages change) or Single Sweep mode.?
Q109
Collector +65V before sweep begins, changes to -9V during sweep, then returns to +65V Emitter -9.39V changes to -9.09V and returns Base -11.6V changes to -8.5V and return
DS101 illuminates during sweep (regardless of length of sweep) and only during sweep. V105 illuminates only while S105 is pressed.?
If S105 is pressed and held, the sweep DOES NOT repeat. During the sweep, DS101 illuminates. When the sweep ends, DS101 extinguishes, whether S105 is held closed or not. S105 must be cycled OFF-ON to sweep again.?
Jeremy, Neither NORMAL or SINGLE will cause the lamp to light but the LED lights properly in either mode. The voltage at Q109's collector is what's puzzling me.? When I first turn it on, the voltage is somewhere close to the value on the schematic (I don't recall the exact voltage); however, after a few seconds, the voltage drops significantly to somewhere close to what I listed and if I recall, it continues to slowly drift towards zero over a period of 20 or 30 seconds.? I'm not sure what that voltage will settle to if I turn it on in SINGLE mode and no triggering event occurs. I know that neon lamps do not need the firing voltage maintained in order to keep the lamp on but 52V seems quite low and that doesn't take into consideration how much voltage R135 drops so that would be just a bit less than 52V across the lamp. It would be interesting to know what you see for the voltage at Q109's collector in your 1421A. Thanks again, Barry - N4BUQ Barry, what happens when you go to Single Sweep and press Reset switch S105??
My schematic (and yours) shows the Collector of Q109 at +48V but your measurement shows -0.33V??
IIRC, when I had the front panel off for cleaning, I inspected those and I _think_ they were very close.? Although I don't know why, they used 1% resistors there.? Of course, that doesn't prevent them from drifting but I do think they were quite close to spec.
Thanks,
Barry - N4BUQ
----- Original Message -----
> From: "Peter Gottlieb" <hpnpilot@...>
> To: "HP-Agilent-Keysight-equipment" <[email protected]>
> Sent: Sunday, April 14, 2024 9:07:32 PM
> Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the Malfunctioning Time Base RESET Lamp in my
> HP-1421A.
> If you can lift Q109C then you could at least measure the sum of those two
> resistors.? But it would be nice to be able to measure the junction of them.
>
> On 4/14/2024 9:55 PM, n4buq via wrote:
>> I'll try grounding the collector of Q109.? Unfortunately, lifting one lead of
>> R136 isn't quick.? The front panel has to be removed to gain access to the
>> small assembly that holds DS101, R135, and R136.? It's too cramped to get to it
>> from the back side of the front of the chassis.
>>
>> Thanks,
>> Barry - N4BUQ
>>
>> ----- Original Message -----
>>> From: "Peter Gottlieb" <hpnpilot@...>
>>> To: "HP-Agilent-Keysight-equipment" <[email protected]>
>>> Sent: Sunday, April 14, 2024 8:10:33 PM
>>> Subject: Re: [HP-Agilent-Keysight-equipment] More Investigation of the
>>> Malfunctioning Time Base RESET Lamp in my
>>> HP-1421A.
>>> Let's go real simple.? You report the collector of Q109 is at essentially
>>> ground, right?
>>>
>>> So if you ground it, and ASSUMING R135 AND R136 HAVEN'T DRIFTED, the neon should
>>> see 86.9 volts, which should light it.
>>>
>>> Neons when new fire somewhere in the 65 volt range but when old can easily drift
>>> upwards, even higher than that voltage.? And resistors can and do drift out of
>>> tolerance.
>>>
>>> Check R135 and R136 values.? Then ground Q109 collector and measure the junction
>>> of R135 and R136 voltage.? If you see near 86.9 volts your neon is old and has
>>> too high a firing voltage.
>>>
>>> Quick and dirty, try lifting one lead of R136 and see if the neon lights then.
>>>
>>> Peter
>>>
>>>
>>> On 4/14/2024 8:59 PM, n4buq via wrote:
>>>> (New thread due to very incorrect subject line and opening paragraph in
>>>> previous thread.)
>>>>
>>>> I still have not determined why DS101 will not turn on in my HP-1421A
>>>> time-base.? I can ground Q109's base through a resistor and force the lamp to
>>>> turn on.? I can place a 1K resistor in parallel with R137 and also force the
>>>> lamp to turn on; however, nothing else works. I thought that the neon might
>>>> have aged to the point where there isn't sufficient striking voltage for it
>>>> but since it will turn on with these methods, that doesn't seem to be case(?).
>>>>
>>>> Setting the unit up as described in the manual for voltage tests, I get the
>>>> following:
>>>>
>>>> -100V F(B): -99.9V
>>>>
>>>> Q109
>>>> Emitter: -9.35V
>>>> Base: -8.78V
>>>> Collector: -0.33V
>>>>
>>>> Q110
>>>> Emitter: -8.01V
>>>> Base: -8.11V
>>>> Collector: -3.7V
>>>>
>>>> Given those values, it would appear (at least to me) that the lamp should turn
>>>> on but it doesn't.
>>>>
>>>> As a test, I disconnected R136/DS101 (the yellow (4) wire) from the board and
>>>> connected a battery, resistor, and LED between GND and the collector of Q109.
>>>> This works just as it should (i.e. the LED turns on when the sweep is
>>>> triggered, turns off at the end of the sweep, and repeats that).
>>>>
>>>> Is it possible that Q109 is not able to conduct enough current to turn DS101
>>>> on but enough to make the LED work?? That seems unlikely but, at this point, I
>>>> don't have any other explanation.
>>>>
>>>> Any help with this is appreciated.
>>>>
>>>> Thanks,
>>>> Barry - N4BUQ
>>>>
>>>>
>>>
>>>
>>>
>>
>>
>>
>>
>
>
>
>
|
Jeremy Nichols