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Re: 7B50 - No Trace

 

On Thu, Nov 18, 2021 at 07:50 AM, n4buq wrote:

I checked the base voltage of Q224/Q234 with the SLOPE in + and -
mid-positions. In both cases, Q224's base is ~ 0.78V and Q234's base is ~
1.62V.
We expect base voltages of Q234 to change with LEVEL knob (pot) but SLOPE control shouldn't make any difference. Q224 base will be at about trigger input voltage + 0.78V and Q234 base should be adjustable above and below 0.78V with the LEVEL knob.

I checked the voltage at the "CQ" point (junction of
R248/R260/CR245/C248) does not change when I rotate through the 12:00
position
and I think S260 is not working properly (not opening).
Similarly LEVEL knob shouldn't have any effect at "CQ" but slope knob +'ve should give you ~ 15V and slope -'ve should give you ~7V at "CQ".


I know that when I was watching the signal at TP262, rotating the SLOPE
control
from -, through mid-position, and then to +, a - slope would cause the
square
wave to appear, it would go to a steady-state (SLOPE pointing to 12:00) and
Isn't SLOPE a switch that goes between two positions, how does it stay at 12:00 position? I am thinking of two concentric knobs, outside is the switch, inside is the LEVEL potentiometer.

Ozan
Re: 7B50 - No Trace

 

Regarding S260, I see now on the schematic that the connector numbers for P260 are shown (3 and 6) so I can follow those and check the switch.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "n4buq" <n4buq@...>
To: "tekscopes" <[email protected]>
Sent: Thursday, November 18, 2021 9:22:32 AM
Subject: Re: [TekScopes] 7B50 - No Trace
Hi Ozan,

I'm not sure but I think I may have found problem with the LEVEL/SLOPE control.
I checked the base voltage of Q224/Q234 with the SLOPE in + and -
mid-positions. In both cases, Q224's base is ~ 0.78V and Q234's base is ~
1.62V. I checked the voltage at the "CQ" point (junction of
R248/R260/CR245/C248) does not change when I rotate through the 12:00 position
and I think S260 is not working properly (not opening).

I know that when I was watching the signal at TP262, rotating the SLOPE control
from -, through mid-position, and then to +, a - slope would cause the square
wave to appear, it would go to a steady-state (SLOPE pointing to 12:00) and
then the square wave would reappear as the slope control was further rotated to
the + side. I don't know whether S260 was actually working when I was looking
at that trace or whether the pot was causing the square wave to reappear
strictly due to the resistance changes.

I'm not very fond of that particular type of control. There is very little, if
any, indication when the maximum or minimum is reached and it is very easy to
rotate it continuously in either direction. I have a 7B80 that has a separate
rotary switch that gives a very positive "click" between slope directions which
works very well.

I removed the S260 assembly last night but I'm not sure which contacts are
associated with S260 and which ones are associated with the various stacked
pots. I'm unsure how to disassemble the stacked elements to determine if the
switch is physically damaged so I'm a bit stuck. If anyone on the list knows
which contacts are which on that assembly, please let me know. Until I can get
this verified, I'm not sure of whether it makes sense to continue with the rest
of the troubleshooting.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Ozan" <ozan_g@...>
To: "tekscopes" <[email protected]>
Sent: Wednesday, November 17, 2021 9:09:11 PM
Subject: Re: [TekScopes] 7B50 - No Trace
Hi Barry,
My comments are below:

On Wed, Nov 17, 2021 at 04:03 PM, n4buq wrote:
...
I presume you want "-" slope so as to disconnect the CQ connection point from
the rest of the circuits.
There is a subtle reason. If you are interested (otherwise skipping is fine): We
want to turn off the current to CR262 to see if it goes to low voltage state.
With -'ve slope Q244 path is selected, to turn off Q244 we turn on Q224 (and
turn off Q234). Base of Q244 is at a known voltage ~ Vbe+little offset (you
measured 0.786V which is fine). This way we can predict most of other voltages.
When +'ve selected we need to turn on Q234 to achieve the opposite effect but
its base voltage depends on the level knob so voltages are a little harder to
predict accurately.


We expect :
At base of Q224 ~ 0.6V [0.786V]
At base of Q234 at least 1V below base of Q224 [1.586V -- presume this is a
problem?]
Perhaps I got it wrong, does turning LEVEL knob all the way CCW decrease Q234
base voltage or increase it? How about all the way CW? We want to make base
voltage of Q234 below base voltage of Q224. When not in P-P Auto mode Level
knob should be able change Q234 base voltage above and below 0.7V.

Top of R224 ~ 10V ( +/1V is OK) [9.12V]
Base of Q244 ~ 1V below Top of R224. [9.12V]
This one and next one are swapped because of base voltage of Q234.

Base of Q254 ~ About same as top of R224. [8.22V]
These look OK except they are swapped. Otherwise one is at 9.12V and the other
is at ~9.12V-1V.

This should turn off all the current in Q244.
Because of the above reason instead of Q244 turning off now it is pulling ~ 10mA
(full on).

Measure voltage across R262 to find out current (Voltage at TP262/2k =~ 6mA
expected). [1.462V/100 ~= 15mA]
R262 passes sum of R261 and collector current. R261 current is 11.1/2k, plus
collector current of 10mA =~ 15mA. Matches the expectation given the swap.


TP262's voltage is 11.1V which, if R261 is close to 2k, that's approximately
6mA as you note. Resistance across R261 checks around 200 ohms which I
presume is due to parallel resistance somewhere(?).
Yes, there is R267+R264 path to +15V supply.

Measure voltage across R267 (should be same as voltage across CR262), also
note
the resistor value (it is selected) and find the current through R267.
[0.477V and 3.0 ohms!]

R267 is marked as 39 ohms. If, indeed, it is now 3 ohms, then that would be
160mA which doesn't seem correct at all. I measured several times with the
probes in both directions. With the + probe at the junction of CR262, I get
2.8 ohms. With the - probe at that junction, I get 3.0 ohms. I don't know if
that's significant but I did notice that. Is this possibly due to CR262 or
could C267 be leaking?
This is bit of a good news. It says the TD is mostly working, when you use a
ohm-meter that doesn't pass enough current TD will look like a short circuit.
It is the low voltage state (I don't know if there is a better official term).

It's a dogbone and I didn't think those were
troublemakers but I suppose anything's possible. I think I can lift the end
of R267 to confirm it's true value if you think that's necessary.
I don't think it is necessary yet. This part of the circuit is best left
untouched.


If all the R262 current is going through R267 then TD is open circuit.
With the weirdness around measuring R267, I'm not sure if this points to the
TD or what.
We couldn't turn off the current to TD. It doesn't say much yet. Only news is
most likely TD is fine.


I'm going to hold off checking the TPs below until I hear back from you
regarding the above as it appears there are problems with those readings. The
TPs below are on the side that's difficult to get to (I don't have an
extender) and if I put that plugin in the left (vertical) bay such that I can
access them better, I'm not sure if that would yield meaningful readings on
Horizontal plugins do generate sweeps/waveforms in vertical slots if externally
triggered. However, it is simpler to attack one problem at a time.

Ozan
Re: 7B50 - No Trace

 

Hi Ozan,

I'm not sure but I think I may have found problem with the LEVEL/SLOPE control. I checked the base voltage of Q224/Q234 with the SLOPE in + and - mid-positions. In both cases, Q224's base is ~ 0.78V and Q234's base is ~ 1.62V. I checked the voltage at the "CQ" point (junction of R248/R260/CR245/C248) does not change when I rotate through the 12:00 position and I think S260 is not working properly (not opening).

I know that when I was watching the signal at TP262, rotating the SLOPE control from -, through mid-position, and then to +, a - slope would cause the square wave to appear, it would go to a steady-state (SLOPE pointing to 12:00) and then the square wave would reappear as the slope control was further rotated to the + side. I don't know whether S260 was actually working when I was looking at that trace or whether the pot was causing the square wave to reappear strictly due to the resistance changes.

I'm not very fond of that particular type of control. There is very little, if any, indication when the maximum or minimum is reached and it is very easy to rotate it continuously in either direction. I have a 7B80 that has a separate rotary switch that gives a very positive "click" between slope directions which works very well.

I removed the S260 assembly last night but I'm not sure which contacts are associated with S260 and which ones are associated with the various stacked pots. I'm unsure how to disassemble the stacked elements to determine if the switch is physically damaged so I'm a bit stuck. If anyone on the list knows which contacts are which on that assembly, please let me know. Until I can get this verified, I'm not sure of whether it makes sense to continue with the rest of the troubleshooting.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Ozan" <ozan_g@...>
To: "tekscopes" <[email protected]>
Sent: Wednesday, November 17, 2021 9:09:11 PM
Subject: Re: [TekScopes] 7B50 - No Trace
Hi Barry,
My comments are below:

On Wed, Nov 17, 2021 at 04:03 PM, n4buq wrote:
...
I presume you want "-" slope so as to disconnect the CQ connection point from
the rest of the circuits.
There is a subtle reason. If you are interested (otherwise skipping is fine): We
want to turn off the current to CR262 to see if it goes to low voltage state.
With -'ve slope Q244 path is selected, to turn off Q244 we turn on Q224 (and
turn off Q234). Base of Q244 is at a known voltage ~ Vbe+little offset (you
measured 0.786V which is fine). This way we can predict most of other voltages.
When +'ve selected we need to turn on Q234 to achieve the opposite effect but
its base voltage depends on the level knob so voltages are a little harder to
predict accurately.


We expect :
At base of Q224 ~ 0.6V [0.786V]
At base of Q234 at least 1V below base of Q224 [1.586V -- presume this is a
problem?]
Perhaps I got it wrong, does turning LEVEL knob all the way CCW decrease Q234
base voltage or increase it? How about all the way CW? We want to make base
voltage of Q234 below base voltage of Q224. When not in P-P Auto mode Level
knob should be able change Q234 base voltage above and below 0.7V.

Top of R224 ~ 10V ( +/1V is OK) [9.12V]
Base of Q244 ~ 1V below Top of R224. [9.12V]
This one and next one are swapped because of base voltage of Q234.

Base of Q254 ~ About same as top of R224. [8.22V]
These look OK except they are swapped. Otherwise one is at 9.12V and the other
is at ~9.12V-1V.

This should turn off all the current in Q244.
Because of the above reason instead of Q244 turning off now it is pulling ~ 10mA
(full on).

Measure voltage across R262 to find out current (Voltage at TP262/2k =~ 6mA
expected). [1.462V/100 ~= 15mA]
R262 passes sum of R261 and collector current. R261 current is 11.1/2k, plus
collector current of 10mA =~ 15mA. Matches the expectation given the swap.


TP262's voltage is 11.1V which, if R261 is close to 2k, that's approximately
6mA as you note. Resistance across R261 checks around 200 ohms which I
presume is due to parallel resistance somewhere(?).
Yes, there is R267+R264 path to +15V supply.

Measure voltage across R267 (should be same as voltage across CR262), also
note
the resistor value (it is selected) and find the current through R267.
[0.477V and 3.0 ohms!]

R267 is marked as 39 ohms. If, indeed, it is now 3 ohms, then that would be
160mA which doesn't seem correct at all. I measured several times with the
probes in both directions. With the + probe at the junction of CR262, I get
2.8 ohms. With the - probe at that junction, I get 3.0 ohms. I don't know if
that's significant but I did notice that. Is this possibly due to CR262 or
could C267 be leaking?
This is bit of a good news. It says the TD is mostly working, when you use a
ohm-meter that doesn't pass enough current TD will look like a short circuit.
It is the low voltage state (I don't know if there is a better official term).

It's a dogbone and I didn't think those were
troublemakers but I suppose anything's possible. I think I can lift the end
of R267 to confirm it's true value if you think that's necessary.
I don't think it is necessary yet. This part of the circuit is best left
untouched.


If all the R262 current is going through R267 then TD is open circuit.
With the weirdness around measuring R267, I'm not sure if this points to the
TD or what.
We couldn't turn off the current to TD. It doesn't say much yet. Only news is
most likely TD is fine.


I'm going to hold off checking the TPs below until I hear back from you
regarding the above as it appears there are problems with those readings. The
TPs below are on the side that's difficult to get to (I don't have an
extender) and if I put that plugin in the left (vertical) bay such that I can
access them better, I'm not sure if that would yield meaningful readings on
Horizontal plugins do generate sweeps/waveforms in vertical slots if externally
triggered. However, it is simpler to attack one problem at a time.

Ozan
Re: TEK 475: Powersupplies repaired, HV CRT circuits fixed (INTENSITY, FOCUS, ASTIGMATISM working) but horizontal Sweep NOT working any more :- (

 

@ Ozan,

Correction: the shorted tantalum was C961 (2.2. uF 20V), fed by a serial resistor of 10 Ohm on the +15V power line..
This shows that such a 10 Ohm series resistor does not protect the tantalum from voltage (current) surges.

The general recommendation to replace tantalums in power rails by equivalents with at least 2.5 X rated voltage, seems to be valid.
It is quite cleat that the TEK engineeers at the time were unaware of this limit of tantalum capacitors! They believed the claims of the makers!

@ Albert Otten,
I have put some pictures and diagrammes on the photo board , but do not know how to link those to this mail.
The offending capacitor is attached to CR1344 and as such deerailed Q1344!


cheers, Martin
7 photos uploaded #photo-notice

[email protected] Notification
 

The following photos have been uploaded to the TEK475 Shorted +15V rail (Intermittent shortcut C961 PLUS intermittent interruption in GND rail. album of the [email protected] group.

By: Redguuz <mgrbosma@...>
Re: 453 trigger issues

[email protected]
 

well,my scope scrubup didnt last long,now neither channels trigger!,it looks shiny tho!
Re: 7k plugins fault finding outside scope?

 

I know there's an extension card on eBay but I'm looking more for something that would have each contact brought out to a through-hole pad such that wires could be soldered to the card edge and then soldered to the connector.

John Griessen's flexible extender kit does what you want. I have used them to check out the caps on a 7A26 applying just +/-15V and watching the current consumption.

Re: 7B50 - No Trace

 

Hi Barry,
My comments are below:

On Wed, Nov 17, 2021 at 04:03 PM, n4buq wrote:
...
I presume you want "-" slope so as to disconnect the CQ connection point from
the rest of the circuits.
There is a subtle reason. If you are interested (otherwise skipping is fine): We want to turn off the current to CR262 to see if it goes to low voltage state. With -'ve slope Q244 path is selected, to turn off Q244 we turn on Q224 (and turn off Q234). Base of Q244 is at a known voltage ~ Vbe+little offset (you measured 0.786V which is fine). This way we can predict most of other voltages. When +'ve selected we need to turn on Q234 to achieve the opposite effect but its base voltage depends on the level knob so voltages are a little harder to predict accurately.


We expect :
At base of Q224 ~ 0.6V [0.786V]
At base of Q234 at least 1V below base of Q224 [1.586V -- presume this is a
problem?]
Perhaps I got it wrong, does turning LEVEL knob all the way CCW decrease Q234 base voltage or increase it? How about all the way CW? We want to make base voltage of Q234 below base voltage of Q224. When not in P-P Auto mode Level knob should be able change Q234 base voltage above and below 0.7V.

Top of R224 ~ 10V ( +/1V is OK) [9.12V]
Base of Q244 ~ 1V below Top of R224. [9.12V]
This one and next one are swapped because of base voltage of Q234.

Base of Q254 ~ About same as top of R224. [8.22V]
These look OK except they are swapped. Otherwise one is at 9.12V and the other is at ~9.12V-1V.

This should turn off all the current in Q244.
Because of the above reason instead of Q244 turning off now it is pulling ~ 10mA (full on).

Measure voltage across R262 to find out current (Voltage at TP262/2k =~ 6mA
expected). [1.462V/100 ~= 15mA]
R262 passes sum of R261 and collector current. R261 current is 11.1/2k, plus collector current of 10mA =~ 15mA. Matches the expectation given the swap.


TP262's voltage is 11.1V which, if R261 is close to 2k, that's approximately
6mA as you note. Resistance across R261 checks around 200 ohms which I
presume is due to parallel resistance somewhere(?).
Yes, there is R267+R264 path to +15V supply.

Measure voltage across R267 (should be same as voltage across CR262), also
note
the resistor value (it is selected) and find the current through R267.
[0.477V and 3.0 ohms!]

R267 is marked as 39 ohms. If, indeed, it is now 3 ohms, then that would be
160mA which doesn't seem correct at all. I measured several times with the
probes in both directions. With the + probe at the junction of CR262, I get
2.8 ohms. With the - probe at that junction, I get 3.0 ohms. I don't know if
that's significant but I did notice that. Is this possibly due to CR262 or
could C267 be leaking?
This is bit of a good news. It says the TD is mostly working, when you use a ohm-meter that doesn't pass enough current TD will look like a short circuit. It is the low voltage state (I don't know if there is a better official term).

It's a dogbone and I didn't think those were
troublemakers but I suppose anything's possible. I think I can lift the end
of R267 to confirm it's true value if you think that's necessary.
I don't think it is necessary yet. This part of the circuit is best left untouched.


If all the R262 current is going through R267 then TD is open circuit.
With the weirdness around measuring R267, I'm not sure if this points to the
TD or what.
We couldn't turn off the current to TD. It doesn't say much yet. Only news is most likely TD is fine.


I'm going to hold off checking the TPs below until I hear back from you
regarding the above as it appears there are problems with those readings. The
TPs below are on the side that's difficult to get to (I don't have an
extender) and if I put that plugin in the left (vertical) bay such that I can
access them better, I'm not sure if that would yield meaningful readings on
Horizontal plugins do generate sweeps/waveforms in vertical slots if externally triggered. However, it is simpler to attack one problem at a time.

Ozan
Re: TEK 475: Powersupplies repaired, HV CRT circuits fixed (INTENSITY, FOCUS, ASTIGMATISM working) but horizontal Sweep NOT working any more :- (

 

Everybody: Thanks for your help and suggestions.

Dear Ozan,

You definitely mentioned C1387 as a potential culprit and helped me locating it (some errors in the manual , hence I could not find it myself!).

The problem of an intermittent tantalum shortcut PLUS an intermittent break in the last part of the GND rail is uncommon.

Next week I will start to look where thee sweep generators have failed ( I think the last part of the horizontal AMP is OK, because the scope functions normally in XY mode and "Beamfinder mode",

I will start a new topic if I get stuck ' I definitely welcome your advice! A new puzzle, I'm afraid!

Regards, Martin
Re: 7B50 - No Trace

 

Comments interleaved with readings in brackets below.

Let's try to reduce CR262 current to see if it will go to low voltage state.
7B50 is in timebase mode (not amplifier)
Triggering in NORM
EXT trigger, DC coupled
No input (or shorted) at EXT trigger
LEVEL knob all the way CCW
Slope -'ve (important)
I presume you want "-" slope so as to disconnect the CQ connection point from the rest of the circuits.

We expect :
At base of Q224 ~ 0.6V [0.786V]
At base of Q234 at least 1V below base of Q224 [1.586V -- presume this is a problem?]
Top of R224 ~ 10V ( +/1V is OK) [9.12V]
Base of Q244 ~ 1V below Top of R224. [9.12V]
Base of Q254 ~ About same as top of R224. [8.22V]
This should turn off all the current in Q244.
Measure voltage across R262 to find out current (Voltage at TP262/2k =~ 6mA
expected). [1.462V/100 ~= 15mA]
TP262's voltage is 11.1V which, if R261 is close to 2k, that's approximately 6mA as you note. Resistance across R261 checks around 200 ohms which I presume is due to parallel resistance somewhere(?).

Measure voltage across R267 (should be same as voltage across CR262), also note
the resistor value (it is selected) and find the current through R267. [0.477V and 3.0 ohms!]
R267 is marked as 39 ohms. If, indeed, it is now 3 ohms, then that would be 160mA which doesn't seem correct at all. I measured several times with the probes in both directions. With the + probe at the junction of CR262, I get 2.8 ohms. With the - probe at that junction, I get 3.0 ohms. I don't know if that's significant but I did notice that. Is this possibly due to CR262 or could C267 be leaking? It's a dogbone and I didn't think those were troublemakers but I suppose anything's possible. I think I can lift the end of R267 to confirm it's true value if you think that's necessary.

If all the R262 current is going through R267 then TD is open circuit.
With the weirdness around measuring R267, I'm not sure if this points to the TD or what.


I'm going to hold off checking the TPs below until I hear back from you regarding the above as it appears there are problems with those readings. The TPs below are on the side that's difficult to get to (I don't have an extender) and if I put that plugin in the left (vertical) bay such that I can access them better, I'm not sure if that would yield meaningful readings on those TPs. I suppose I could remove the amplifier and leave it in a horizontal bay and still reach those so I can try that after I hear back from you.

As for the Lockout:
What voltage do you see at TP525?
What is the state of the sweep signal TP534 (running, railed at ground, railed
at 10.5V, railed above 10.5V)?

Ozan

Thank you so much for helping me with this. I really like my 7B80 and I think it's worth the effort to get these plugins all working as best as I can.

Barry - N4BUQ
Re: TEK 475: Powersupplies repaired, HV CRT circuits fixed (INTENSITY, FOCUS, ASTIGMATISM working) but horizontal Sweep NOT working any more :- (

 

On Wed, Nov 17, 2021 at 12:14 PM, Redguuz wrote:
I managed to repair the CRT circuit of my TEK 475. The screen intensity
control and focus, is currently working as I should.
Congratulations for the fix Martin.

By coincidence I found the cause (i.e. the offending tantalum C1387 ( wrong
labelled C126 in the photo Fig. 7.19) , 2.2 uF, 20V in the +15V power rail),
next to the ceramic plate.
I was guessing in the same area but I don't know if I got it right in my message /g/TekScopes/message/187822
Mystery solved!
Ozan
Re: TEK 475: Powersupplies repaired, HV CRT circuits fixed (INTENSITY, FOCUS, ASTIGMATISM working) but horizontal Sweep NOT working any more :- (

 

Good find Martin!

(i.e. the offending tantalum C1387 ( wrong labelled C126 in the photo Fig. > 7.19)
Not important: In my 475 pdf C1387 is shown correctly I think in location 7D. But despite my new glasses I can't find C1387 in diagram <12>.
Albert
Re: Horizontal preamplifier #chat-notice

 

Did you check the connections to the plates, as Raymond suggested?

Sent from my iThing, so please forgive typos and brevity.

On Nov 17, 2021, at 3:20 AM, michel.breucker@... wrote:

?The trace on the screen begins in the middle of it. I suspect the horizontal preamp 155-0124. Can someone help me? Does anyone have such a circuit? Thank you
Re: TEK 475: Powersupplies repaired, HV CRT circuits fixed (INTENSITY, FOCUS, ASTIGMATISM working) but horizontal Sweep NOT working any more :- (

 

On Wed, Nov 17, 2021 at 09:14 PM, Redguuz wrote:


I managed to repair the CRT circuit of my TEK 475.
Goed gedaan, Martin! (Well done, Martin!)

Raymond
Re: TEK 475: Powersupplies repaired, HV CRT circuits fixed (INTENSITY, FOCUS, ASTIGMATISM working) but horizontal Sweep NOT working any more :- (

 

Hi,

I managed to repair the CRT circuit of my TEK 475. The screen intensity control and focus, is currently working as I should.

I now can create nice, sharp horizontal and vertical lines in the XY mode.
Screen Intensity Control, Focus and astigmatism do all work.
The CRT is NOT defective as I had feared.

The fault in the end was still the rather familiar (intermittently) shorted Tantalum Capacitor in this case C 1387 in the +15V power rail.

I had measured all components around the CRT with Power Off; All OK, also the Restorer diodes.

But whilst measuring "dry" on these circuits, the short circuit in the +15 V returned again!.

By coincidence I found the cause (i.e. the offending tantalum C1387 ( wrong labelled C126 in the photo Fig. 7.19) , 2.2 uF, 20V in the +15V power rail), next to the ceramic plate.

Previously I had observed that the short in the15V rail vanished by pushing/pulling on the Interface PCB.
It reacted strongly in the vicinity of the back of the scope, but I could not really locate it.
(I thought the short circuit occurred at the backside of the board against the chassis.
In the end, I could get a stable (61.2 Ohm vs GND : i.e. No Short Circuit) on +15V rail, if a removed the LH Bottom pillar of the Safety protection cover.
I thought I had solved the problem, see previous mails.

But only now I found out that removing this pillar (intermittently) cuts out the trace of the earth rail of the +15V (on whichthe offending tantalum C1387 2.2 uF, only 20V! was located.
So, the +15 V rail was still shorted All Right at the end of the rail (and I had only unintentionally disconnected (part of) the GND rail).

Bij measuring the resistance between the + 15V and that shorted part the GND Rail, while scanning around this GND rail with a sensitive Ohm meter, I could clearly measure that the short was at the C1387 location

Removing this capacitor, indeed removed the short.

When I powered up the scope, the INTENSITY, FOCUS and ASTIGMATISM all worked OK.

The unfortunate thing is that I somehow lost the Horizontal sweep (A en B).

(In the XY mode the scope works as it should), but the sweep is dead.
The vertical amplifiers are AllRight and I can move lines horizontally and vertically in XY mode and in "Beam finder" mode.
So the fault is located more "upstream".

O well, back to the drawing board to diagnose why the Horizontal Sweep did quit (I have not touched it all and was extremely careful, both mechanically and electronically).
(Maybe the "floating 15V GND section did destroy something.)

But many thanks to you all with helping me with (understanding/troubleshooting) the CRT circuit.

Will be continued ( I will start a new topic, if I have any questions).

Martin
Re: 453 trigger issues

 

Thank you Mike! I will bookmark those articles.

By the way, the individual files of Service Scope and TekScope are hosted at Kurt Rosenfeld¡¯s excellent TekWiki site, w140.com .

Dave Wise
Information Display Division, 1980-1995

From: [email protected] [mailto:[email protected]] On Behalf Of Mike Merigliano via groups.io
Sent: Wednesday, November 17, 2021 10:47 AM
To: [email protected]
Subject: Re: [TekScopes] 453 trigger issues

Hello,

The first one in Charles Phillips' series was in February 1969. This is
the volume when Service Scope was renamed "TEKscope", which in turn
includes Service Scope. The look changed somewhat as well, and they
started with Volume 1 Number 1 that month and year, but the volume and
number information is not at the first page. I am hardly an expert on this.

Articles:

Troubleshooting Your Oscilloscope. February 1969, page 8 to 11 (volume 1
number 1)

Troubleshooting the Power Supply. April 1969, page 12 to 14 (volume 1
number 2)

Troubleshooting the High Voltage Supply. June 1969, page 12 to 14
(volume 1 number 3)

Troubleshooting the Trigger Circuits. August 1969, page 12 to 14 (volume
1 number 4)

Troubleshooting the Sweep Circuits. October 1969, page 16 to 19 (volume
1 number 5)

Troubleshooting the Amplifiers. December 1969, page 12 to 14 (volume 1
number 6)

Troubleshooting Preamplifiers. February 1970, page 12 to 14 (volume 2
number 1)

Troubleshooting Sampling Systems. April 1970, page 12 to 14 (volume 2
number 2)

Troubleshooting Sampling Systems, part 2. June 1970, page 12 to 14
(volume 2 number 3)

Troubleshooting the 453. August 1970, page 13 to 15 (volume 2 number 4)

Servicing the C12, C13, C19, and C27 Cameras. October 1970 pages 12 to
15 (volume 2 number 5)

There are more, but maybe this is helpful so far.

On 11/17/2021 9:59 AM, Dave Wise wrote:
Hey Mike, I have Service Scope and TekScope in individual files. Can you tell us the Month/Year or Volume/Number?

Thanks,
Dave Wise

From: [email protected] [mailto:[email protected]] On Behalf Of Mike Merigliano via groups.io
Sent: Wednesday, November 17, 2021 8:02 AM
To: [email protected]
Subject: Re: [TekScopes] 453 trigger issues

The Tektronix "Service Scope" publication had a series of articles by
Charles Phillips. At least two of them maybe helpful:

Troubleshooting the 453

Troubleshooting Trigger Circuits

I think the Tekscopes group site (this one) has the Tekscopes
publication in a pdf from October 1959 to October 1970.

It has 694 pages. The series are scattered through the document and a
5-part series starts on page 422. The trigger article starts on page
474, and the Tek 453 article starts on page 579

I assume that you have the correct Tek 453 manual.

The "Troubleshooting Your Oscilloscope: Getting Down to Basics" is
another good source, and it incorporates some of the Tekscope articles.

Good luck!

On 11/17/2021 6:21 AM, quadzillatech@... wrote:
well heres a few measurements at test points on the trigger board settings are normal rigger horiz display set to A .
tp 714=8.9v
tp 675=5.98v
tp 705=0.38v
tp 604=0.835v goes to -.41v when switched A inten during b
Re: 453 trigger issues

 

Hello,

The first one in Charles Phillips' series was in February 1969. This is the volume when Service Scope was renamed "TEKscope", which in turn includes Service Scope. The look changed somewhat as well, and they started with Volume 1 Number 1 that month and year, but the volume and number information is not at the first page. I am hardly an expert on this.

Articles:

Troubleshooting Your Oscilloscope. February 1969, page 8 to 11 (volume 1 number 1)

Troubleshooting the Power Supply. April 1969, page 12 to 14 (volume 1 number 2)

Troubleshooting the High Voltage Supply. June 1969, page 12 to 14 (volume 1 number 3)

Troubleshooting the Trigger Circuits. August 1969, page 12 to 14 (volume 1 number 4)

Troubleshooting the Sweep Circuits. October 1969, page 16 to 19 (volume 1 number 5)

Troubleshooting the Amplifiers. December 1969, page 12 to 14 (volume 1 number 6)

Troubleshooting Preamplifiers. February 1970, page 12 to 14 (volume 2 number 1)

Troubleshooting Sampling Systems. April 1970, page 12 to 14 (volume 2 number 2)

Troubleshooting Sampling Systems, part 2. June 1970, page 12 to 14 (volume 2 number 3)

Troubleshooting the 453. August 1970, page 13 to 15 (volume 2 number 4)

Servicing the C12, C13, C19, and C27 Cameras. October 1970 pages 12 to 15 (volume 2 number 5)

There are more, but maybe this is helpful so far.

On 11/17/2021 9:59 AM, Dave Wise wrote:
Hey Mike, I have Service Scope and TekScope in individual files. Can you tell us the Month/Year or Volume/Number?

Thanks,
Dave Wise

From: [email protected] [mailto:[email protected]] On Behalf Of Mike Merigliano via groups.io
Sent: Wednesday, November 17, 2021 8:02 AM
To: [email protected]
Subject: Re: [TekScopes] 453 trigger issues

The Tektronix "Service Scope" publication had a series of articles by
Charles Phillips. At least two of them maybe helpful:

Troubleshooting the 453

Troubleshooting Trigger Circuits

I think the Tekscopes group site (this one) has the Tekscopes
publication in a pdf from October 1959 to October 1970.

It has 694 pages. The series are scattered through the document and a
5-part series starts on page 422. The trigger article starts on page
474, and the Tek 453 article starts on page 579

I assume that you have the correct Tek 453 manual.

The "Troubleshooting Your Oscilloscope: Getting Down to Basics" is
another good source, and it incorporates some of the Tekscope articles.

Good luck!

On 11/17/2021 6:21 AM, quadzillatech@... wrote:
well heres a few measurements at test points on the trigger board settings are normal rigger horiz display set to A .
tp 714=8.9v
tp 675=5.98v
tp 705=0.38v
tp 604=0.835v goes to -.41v when switched A inten during b
Re: 7B50 - No Trace

 

On Wed, Nov 17, 2021 at 06:46 AM, n4buq wrote:

I may be misunderstanding the way the SWEEP INHIBIT is supposed to work. I
was checking the signals at the various TPs around Q410, Q416, Q432, and Q436
and those are all showing a fixed voltage. I don't know whether the
main-frame typically toggles that line but I presume so; however, I don't
understand how the MF decides when to toggle it. Fig. 3-7 shows there are two
current states feeding that point but it's unclear to me whether that's
intended to show a constantly-changing current or if it is just indicating
that 0ma is free-running and 1mA or more is an inhibit condition.
I don't know the answer to that, perhaps someone with more experience with 7000 series knows. Reading the interface notes it sounds like MF inhibit is only used in Alternate and delayed B sweep modes.

Lockout (Sweep Reset in Sheet <3>) depends on two signals: Inhibit signal from MF and what happens in the comparator Q406/Q408. That was the reason for my question of TP534, I wanted to see the state of Q406.


Also, you mentioned Vd with respect to CR262 in a previous message. I'm not
sure what that means and am presuming Diode Voltage. Can you clarify that for
me. Sorry if that's a common notation but I don't recall seeing it and don't
find anything Googling for it either.
Yes, it is the diode voltage:

To be proper D has to be an upper case subscript but without subscript Vd looks better than VD for me.

Ozan
Re: Tektronix 576 CRT replacement

 

That's interesting, my 576 had black soot all inside the HV cage and its components,
along the wiring all the way up to the CRT yoke. Do you mean everywhere, or confined to that area?
The soot contaminated several of the open-frame pots so I replaced them, it might
be worth looking at them.
Re: 453 trigger issues

 

From my 453 repair journal:

++++++++++++++++++++
Then I noticed that B trigger wasn't working. The culprit was tunnel
diode D675 (TD3, 4.7mA). Luckily I had a spare.

Later I lost B trigger again. Q684, replaced with Soviet KT3126A.
PNP 20V 20mA 500MHz 2.5pF .
++++++++++++++++++++

HTH,
Dave Wise

From: [email protected] [mailto:[email protected]] On Behalf Of quadzillatech via groups.io
Sent: Tuesday, November 16, 2021 8:11 PM
To: [email protected]
Subject: [TekScopes] 453 trigger issues

hi ive got issues with the triggering on my 453,firstly it wouldnt trigger on ch A or B,i washed the whole scope down in the shower and dried it,it now works fine on ch a but has a hard time triggering on ch b,its odd if i remove q454 and q 464 it makes no difference,the displayed waveform is very jittery but sort of triggers,the level control seems very sharp on chB but normal on ch A,any idea where i start looking? q454 was dead so replaced it but made no difference i suspect a cap ,Its a later scope with the fet front end.
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