Re: small jewel light Tek 561A
the service manual specs a G.E. #12
?
In a message dated 7/19/2012 5:48:03 A.M. Pacific Daylight Time,
murks24@... writes:
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what is please the name of the bulb in the little jewel light from Tek
561A?
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I have a TDS784D where all four ceramic attenuator hybrids are cracked. I'm looking for replacements, and would like to know if any other models use compatible attenuators. Would the attenuators from a TDS744A work (even partially so I can check the rest of the scope)?
If anyone knows where I might be able to find them at a reasonable cost, I would love to hear from you. I'll take one with SPC problems since I know I can replace the relays.
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Re: Tektronix 475 with no display
I think you need to change C-1412 also.
?
Can you take a look at the ripple on the 110 volt?test point? Be
careful. 110 volts hurts a bit.
?
Tom
?
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----- Original Message -----
Sent: Thursday, July 19, 2012 5:31
PM
Subject: Re: [TekScopes] Tektronix 475
with no display
?
So I replaced the two capacitors (C1414 and C1442), reviewed the schematic
and made sure that any connected points were still making contact (need to add
a jumper from C1442 to CR1415, due to my removal accident where I damaged a
trace).?
I backed off the +50V adjustment, fired it up, adjusted it back to 50.0V
and now I get the following:
+50=50.0V
+110=91.0V
+15=15.0V
+5=5V
-15=-14.8V
-8=-7.9V
+105=132.0V
UNREG 50=~66V
Now, those all look to be within spec except for +110 (at 91V) and
possibly the 105 (at 132, schematic shows 136). I did some searching/testing
and didn't see anything major wrong, so I tested the resistance values.
TP - expected - measured
110 - 11K - >20K (too high)
50 - 2.7K - 2.7K (perfect)
15 - 63 - 66.3 (within range)
5 - 46 - 49.9 (within range)
-15 - 480 - 12.9K (too high)
-8 - 32 - 31.2 (within range)
UNREG 50 - 14K - >20K (too high)
105 - 12K - >20K (too high)
So my 110 and 105 lines are both showing low voltage, so the higher
resistance made sense to me. But the high resistance on the -15 line seemed
odd. My assumption is that it means the voltage compensation is working
overtime and properly correcting for an issue somewhere. Is that
correct?
In reading the service manual, it states to attempt to test the
rectifier, the current-limiting transistor, and the op amp. I see that the 105
and 110 both get fed from the +50V rectifier as well as the 110 op-amp pulling
from the regulated 50V line.
When I get home from work, I intend to test the 50V supply area more.
What I'm wondering is if anything I've stated throws an "obvious" flag for
anyone with more experience. When I tested the current-limiting transistor for
the 50V section, it had some voltage (the manual states it should be "off",
which I take to mean 0V). I'm just not sure if that's the cause of the issue,
or a result.
Based on some time staring at the manual, I'm assuming the rectifier is
more of an issue, but that's a guess.
Also, as a side note, I can get a line when I press the beam finder
button now (I did not previously). So some progress is being made (aside from
the obvious progress of mostly-proper voltages).
One final thing to mention: This morning I powered it up before heading
to work, just to make sure I had noted the proper values. When I did that, the
voltage readings were better on 110 and 105 (94, 136.9 respectively). But as a
minute or two went by, and things warmed up, the voltages started to drop.
Again, this tends to make sense to me as something is most likely expanding,
providing more resistance, and cutting down the potential. Any
confirmation/correction would be appreciated.
Also, again, those caps are tricky. I've been soldering (hobbiest, not
full-time) for at least 15 years, and I had a rough time replacing the caps.
Everything works and tests out nicely, but it doesn't look so great (good
joints, but heat marks, etc). I'm definitely not used to this older style of
circuit board. Way too easy to lift traces, but that was a good lesson
learned.
As always, thanks for all of the information. It's been greatly useful
for my learning process.
-Josh
On Mon, Jul 16, 2012 at 11:08 AM, David <davidwhess@...> wrote:
?
On Mon, 16 Jul 2012 10:25:01 -0500, " fakecrap@..." < fakecrap@...>
wrote: >Great info, thanks. I was under the impression that I
should replace with >like-sized capacitance and at least similar
voltage (higher being OK as >well). In high ripple
current applications, sometimes higher voltage capacitors than strictly
necessary are used because the larger physical size can dissipate more
heat so they last longer.
>I assume the capacitance is OK to increase because
it's a power supply and
>gets regulated afterword,
correct?
It is fine within reason. Increasing the capacitance
could increase the startup current or delay the startup in a switching
power supply. In this case it is a standard 60Hz rectifier and capacitor
filter so the surge current will be higher with more capacitance. I would
use the same value or the next higher standard value if I was
being conservative.
>Either way, I'll order some of those up and see
what happens. I'm thinking
>I'll leave others alone, but I'm still
internally re-hashing the age-old
>debate of whether or not to just
replace all the big cans while I'm at it.
If the failure is age
related, then I usually replace all of the similar capacitors.
|
Re: Tektronix 475 with no display
So I replaced the two capacitors (C1414 and C1442), reviewed the schematic and made sure that any connected points were still making contact (need to add a jumper from C1442 to CR1415, due to my removal accident where I damaged a trace).?
I backed off the +50V adjustment, fired it up, adjusted it back to 50.0V and now I get the following: +50=50.0V +110=91.0V +15=15.0V +5=5V -15=-14.8V -8=-7.9V
+105=132.0V UNREG 50=~66V
Now, those all look to be within spec except for +110 (at 91V) and possibly the 105 (at 132, schematic shows 136). I did some searching/testing and didn't see anything major wrong, so I tested the resistance values.
TP - expected - measured 110 - 11K - >20K (too high) 50 - 2.7K - 2.7K (perfect) 15 - 63 - 66.3 (within range) 5 - 46 - 49.9 (within range) -15 - 480 - 12.9K (too high)
-8 - 32 - 31.2 (within range) UNREG 50 - 14K - >20K (too high) 105 - 12K - >20K (too high)
So my 110 and 105 lines are both showing low voltage, so the higher resistance made sense to me. But the high resistance on the -15 line seemed odd. My assumption is that it means the voltage compensation is working overtime and properly correcting for an issue somewhere. Is that correct?
In reading the service manual, it states to attempt to test the rectifier, the current-limiting transistor, and the op amp. I see that the 105 and 110 both get fed from the +50V rectifier as well as the 110 op-amp pulling from the regulated 50V line.
When I get home from work, I intend to test the 50V supply area more. What I'm wondering is if anything I've stated throws an "obvious" flag for anyone with more experience. When I tested the current-limiting transistor for the 50V section, it had some voltage (the manual states it should be "off", which I take to mean 0V). I'm just not sure if that's the cause of the issue, or a result.
Based on some time staring at the manual, I'm assuming the rectifier is more of an issue, but that's a guess.
Also, as a side note, I can get a line when I press the beam finder button now (I did not previously). So some progress is being made (aside from the obvious progress of mostly-proper voltages).
One final thing to mention: This morning I powered it up before heading to work, just to make sure I had noted the proper values. When I did that, the voltage readings were better on 110 and 105 (94, 136.9 respectively). But as a minute or two went by, and things warmed up, the voltages started to drop. Again, this tends to make sense to me as something is most likely expanding, providing more resistance, and cutting down the potential. Any confirmation/correction would be appreciated.
Also, again, those caps are tricky. I've been soldering (hobbiest, not full-time) for at least 15 years, and I had a rough time replacing the caps. Everything works and tests out nicely, but it doesn't look so great (good joints, but heat marks, etc). I'm definitely not used to this older style of circuit board. Way too easy to lift traces, but that was a good lesson learned.
As always, thanks for all of the information. It's been greatly useful for my learning process.
-Josh
On Mon, Jul 16, 2012 at 11:08 AM, David <davidwhess@...> wrote:
?
On Mon, 16 Jul 2012 10:25:01 -0500, " fakecrap@..."
< fakecrap@...> wrote:
>Great info, thanks. I was under the impression that I should replace with
>like-sized capacitance and at least similar voltage (higher being OK as
>well).
In high ripple current applications, sometimes higher voltage
capacitors than strictly necessary are used because the larger
physical size can dissipate more heat so they last longer.
>I assume the capacitance is OK to increase because it's a power supply and
>gets regulated afterword, correct?
It is fine within reason. Increasing the capacitance could increase
the startup current or delay the startup in a switching power supply.
In this case it is a standard 60Hz rectifier and capacitor filter so
the surge current will be higher with more capacitance. I would use
the same value or the next higher standard value if I was being
conservative.
>Either way, I'll order some of those up and see what happens. I'm thinking
>I'll leave others alone, but I'm still internally re-hashing the age-old
>debate of whether or not to just replace all the big cans while I'm at it.
If the failure is age related, then I usually replace all of the
similar capacitors.
|
Re: How to adjust horizontal position of Readout display? R7903
Thanks Tom, I didn't realize a single contact could be replaced. Already have the interface board out, gawd those small bolts holding the four ground straps are tough to position with my fat fingers!
Anyone have a replacement contact/pin they can send me? Contact me off-list.
Thanks,
Keith
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--- In TekScopes@..., "Tom Miller" <tmiller11147@...> wrote:
It is possible to replace just the one contact. Not a fun project as you may want to remove the entire interface board to make it easy. I would guess someone on the list has a parts board and could recover a few pins for you.
Tom
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Re: How to adjust horizontal position of Readout display? R7903
Hi,
It may be possible to reform the pin. They sometimes get pushed back and get stuck trying to spring back. Sometimes they will come back if knugged with a scribe. I have the pins but it may be a week or before I can return to the ranch to get them.
Jerry Massengale
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-----Original Message-----
From: Tom Miller
To: TekScopes <TekScopes@...>
Sent: Thu, Jul 19, 2012 3:14 pm
Subject: Re: [TekScopes] Re: How to adjust horizontal position of Readout display? R7903
?
It is possible to replace just the one contact. Not a fun project as you
may want to remove the entire interface board to make it easy. I would guess
someone on the list has a parts board and could recover a few pins for
you.
?
?
Tom
?
----- Original Message -----
Sent: Thursday, July 19, 2012 4:10
PM
Subject: [TekScopes] Re: How to adjust
horizontal position of Readout display? R7903
?
Found it. Tried several things, but after looking very carefully found that
the A38 spring (correct term?) is broken. See photo:
It's
the curved part of the metal spring that the card would press against that is
broken off. So the card is just not able to make a good connection in the J2
connector at A38.
Is there a practical fix for this? Replacing the
entire connector is probably not gonna happen. Maybe some way of soldering
some kind of conductive shim? I have a feeling that type metal doesn't take to
soldering easily, and in really tight, tiny quarters....
I am assuming
there isn't a way to replace just the spring metal for that one pin, is that
correct?
Ideas? Rob, maybe you've faced this before?
Keith
Ostertag
|
Re: How to adjust horizontal position of Readout display? R7903
It is possible to replace just the one contact. Not a fun project as you
may want to remove the entire interface board to make it easy. I would guess
someone on the list has a parts board and could recover a few pins for
you.
?
?
Tom
?
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Show quoted text
----- Original Message -----
Sent: Thursday, July 19, 2012 4:10
PM
Subject: [TekScopes] Re: How to adjust
horizontal position of Readout display? R7903
?
Found it. Tried several things, but after looking very carefully found that
the A38 spring (correct term?) is broken. See photo:
It's
the curved part of the metal spring that the card would press against that is
broken off. So the card is just not able to make a good connection in the J2
connector at A38.
Is there a practical fix for this? Replacing the
entire connector is probably not gonna happen. Maybe some way of soldering
some kind of conductive shim? I have a feeling that type metal doesn't take to
soldering easily, and in really tight, tiny quarters....
I am assuming
there isn't a way to replace just the spring metal for that one pin, is that
correct?
Ideas? Rob, maybe you've faced this before?
Keith
Ostertag
|
Re: How to adjust horizontal position of Readout display? R7903
Found it. Tried several things, but after looking very carefully found that the A38 spring (correct term?) is broken. See photo:
It's the curved part of the metal spring that the card would press against that is broken off. So the card is just not able to make a good connection in the J2 connector at A38.
Is there a practical fix for this? Replacing the entire connector is probably not gonna happen. Maybe some way of soldering some kind of conductive shim? I have a feeling that type metal doesn't take to soldering easily, and in really tight, tiny quarters....
I am assuming there isn't a way to replace just the spring metal for that one pin, is that correct?
Ideas? Rob, maybe you've faced this before?
Keith Ostertag
|
Re: Spark gaps firing on 7854 PSU
For 230V operation the manual is a bit misleading, in only saying that E8 and E13 are in series and fire when the line voltage peaks over 460 V. Each spark gap is between the caps center tap and one of the line inputs. If a cap shorts (or when the capacitances are very different, during start-up) then one of the gaps will fire even when the line voltage is normal.
Albert
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--- In TekScopes@..., David <davidwhess@...> wrote:
Step D on page 3-14 of the service manual discusses troubleshooting of
the line input section of the power supply. I would start there but
they use a variac to produce a 20VAC line power input for testing.
I would certainly check those big reservoir capacitors to see if one
or both are bad or marginal. Sometimes they fail open which is easy
to verify.
On Thu, 19 Jul 2012 18:12:25 +0100, "David C. Partridge"
<david.partridge@...> wrote:
My 7854 wouldn't play today, initially ticking, then just sulking and blowing 3A fuses on my isolation transformer.
Before I swapped the PSU as I was in hurry to get the 'scope working, I did notice (hard to miss really) that when I turned the power on, both the spark gaps in the mains input area of the inverter board fired brightly for a moment. I also saw that the voltage across C16 and C17 didn't match and the waveform on the caps was kinda weird.
Does firing spark gaps suggest the big reservoir caps are sick? Is there anything else likely to cause that?
Thanks,
David Partridge
|
Re: How to adjust horizontal position of Readout display? R7903
If either the row or column signal was shorted or open, that would cause a blank display. You may want to examine the right vertical edge connector carefully with a bright light. Maybe the A38 or B38 left spring is damaged. Check the protection diodes on the A38 and B38 signals for the second vertical bay. One may be shorted. They are CR2245, CR2246, CR2261, and CR2262 (or check them all since it is easy enough to do). On a 7904 you could swap P2265 and P2266 at the readout board causing the vertical and horizontal readouts to be swapped but the 7903 lacks horizontal B connections so that will not help in your case. On Thu, 19 Jul 2012 18:02:40 -0000, "keithostertag" <keitho@...> wrote: David- Thanks much. I had seen the one sentence in the manual stating that data for channel 2 of a dual channel plugin is routed via A38 and B38, but I hadn't gotten far enough along in my thinking to follow up on it. I'm still not good at reading schematics.
Yes, vertical channel 1 right works fine.
I decided to swap the entire readout board from my 7844 to the R7903, since they are the same board. No change- right vertical chanel 2 still does not display. So this clues me into looking more closely into the connectors from the backplane through A4 to the readout board...
Thanks,
Keith Ostertag
--- In TekScopes@..., David <davidwhess@...> wrote:
The horizontal readout centering does not look that far off to me. I
would check and calibrate the horizontal CRT centering before deciding
it is a problem.
Does the right vertical channel 1 readout work correctly? Did you
really have it set to 1 volt/div and uncalibrated when you took the
picture?
If the right vertical channel 1 readout is working correctly, then we
know the time slot signals are making it to the right vertical. I
suspect we will find that there is a broken connection between either
the right vertical channel 2 column (pin A38 to pin 11 of U2190) or
the right vertical channel 2 row (pin B38 to pin 11 of U2180) and the
readout circuits.
There are a few connectors that should be inspected between the
readout board and the backplane board that carry those signals.
|
Re: Spark gaps firing on 7854 PSU
Step D on page 3-14 of the service manual discusses troubleshooting of the line input section of the power supply. I would start there but they use a variac to produce a 20VAC line power input for testing. I would certainly check those big reservoir capacitors to see if one or both are bad or marginal. Sometimes they fail open which is easy to verify. On Thu, 19 Jul 2012 18:12:25 +0100, "David C. Partridge" <david.partridge@...> wrote: My 7854 wouldn't play today, initially ticking, then just sulking and blowing 3A fuses on my isolation transformer.
Before I swapped the PSU as I was in hurry to get the 'scope working, I did notice (hard to miss really) that when I turned the power on, both the spark gaps in the mains input area of the inverter board fired brightly for a moment. I also saw that the voltage across C16 and C17 didn't match and the waveform on the caps was kinda weird.
Does firing spark gaps suggest the big reservoir caps are sick? Is there anything else likely to cause that?
Thanks,
David Partridge
|
Re: How to adjust horizontal position of Readout display? R7903
David- Thanks much. I had seen the one sentence in the manual stating that data for channel 2 of a dual channel plugin is routed via A38 and B38, but I hadn't gotten far enough along in my thinking to follow up on it. I'm still not good at reading schematics.
Yes, vertical channel 1 right works fine.
I decided to swap the entire readout board from my 7844 to the R7903, since they are the same board. No change- right vertical chanel 2 still does not display. So this clues me into looking more closely into the connectors from the backplane through A4 to the readout board...
Thanks,
Keith Ostertag
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Show quoted text
--- In TekScopes@..., David <davidwhess@...> wrote:
The horizontal readout centering does not look that far off to me. I
would check and calibrate the horizontal CRT centering before deciding
it is a problem.
Does the right vertical channel 1 readout work correctly? Did you
really have it set to 1 volt/div and uncalibrated when you took the
picture?
If the right vertical channel 1 readout is working correctly, then we
know the time slot signals are making it to the right vertical. I
suspect we will find that there is a broken connection between either
the right vertical channel 2 column (pin A38 to pin 11 of U2190) or
the right vertical channel 2 row (pin B38 to pin 11 of U2180) and the
readout circuits.
There are a few connectors that should be inspected between the
readout board and the backplane board that carry those signals.
|
Spark gaps firing on 7854 PSU
My 7854 wouldn't play today, initially ticking, then just sulking and blowing 3A fuses on my isolation transformer.
Before I swapped the PSU as I was in hurry to get the 'scope working, I did notice (hard to miss really) that when I turned the power on, both the spark gaps in the mains input area of the inverter board fired brightly for a moment. I also saw that the voltage across C16 and C17 didn't match and the waveform on the caps was kinda weird.
Does firing spark gaps suggest the big reservoir caps are sick? Is there anything else likely to cause that?
Thanks,
David Partridge
|
Re: How to adjust horizontal position of Readout display? R7903
The horizontal readout centering does not look that far off to me. I would check and calibrate the horizontal CRT centering before deciding it is a problem. Does the right vertical channel 1 readout work correctly? Did you really have it set to 1 volt/div and uncalibrated when you took the picture? If the right vertical channel 1 readout is working correctly, then we know the time slot signals are making it to the right vertical. I suspect we will find that there is a broken connection between either the right vertical channel 2 column (pin A38 to pin 11 of U2190) or the right vertical channel 2 row (pin B38 to pin 11 of U2180) and the readout circuits. There are a few connectors that should be inspected between the readout board and the backplane board that carry those signals. On Thu, 19 Jul 2012 14:59:47 -0000, "keithostertag" <keitho@...> wrote: Thanks David and Magnus for these details- more for me to study and learn.
Here is a photo better showing the problem.
I have loaded the R7903 with plugins with no inputs just to show the readouts. You can see that they are a little too far to the right, which was my original topic. All the characters seem to be displaying correctly.
However, only yesterday (after I started the thread) I noticed that channel 2 right vertical doesn't display the readout (as you can see in the photo). So now I am wondering if there might be a connection between the two issues, maybe not.
My 7A18's have option 6, so they don't have the "Identify" feature. The only vertical amp I have with "Identify" is my one 7A26. I also have a 7B53A loaded just to show that both channel readouts do display for all other slots. The 7A26 displays readout in channel 1 & 2 in the left vertical as expected, so it is not a plugin issue.
If I push the Identify button on the 7A26 I do get both the "Identify" word and the trace moving up a bit, except for channel 2 right vertical. For channel 2 right vertical I do get the trace moving in response to pushing the Identify button, just not the word.
I have been studying the manual, but it's kinda like trying to learn Linux in one day...
So far I have checked the following by swapping with known good chips from my 7844:
U2232 (replacement)
U2250
U2155
U2250 and U2260
U2284
From my reading those would be the most likely IC chips to cause this type of problem (easiest things to check first).
Your thoughts?
Thanks,
Keith Ostertag
--- In TekScopes@..., "magnustoelle" <magnustoelle@...> wrote:
Hello Keith
on your return question:
I don't understand this at all. The vertical amp plugins I have, 7A18 and 7A26, don't have any outputs. Do you mean somehow tap into the circuitry? Do you mean short the backplane pins?
This likely has little to do with the original topic (positioning the Readout), but it's a teaching/learning moment :-)
Thanks,
Keith Ostertag
Yes, this refers to the circuitry.
On the 7A26, you may want to check out the output stages which Q820/Q840 and Q860/Q880 form.
See page 3-3 in the 7A26 Rev C Manual from March 1975 for a description. And refer to schematics DISPLAY SWITCHING AND OUTPUT, number 4 on page number 63.
The contacts relevant for the vertical output signals on the rear connector are A11 (positive signal) and B11 (negative, as this is a differential signal).
Good Luck,
Magnus
|
Re: How to adjust horizontal position of Readout display? R7903
Hmm, the 7903 service manual is organized a lot differently. You want sections 21A through 21C for the horizontal amplifier centering. Hopefully performing them will center the readout also because unlike the 7904, the 7903 lacks a separate horizontal readout centering adjustment. The 7904 horizontal readout centering adjustment is on the horizontal amplifier board. If the 7903 readout is not horizontally centered after the above but is not too far off, I would use the horizontal centering adjustment (R868 or R4868 depending on the 7903 version) to center it and declare victory. If the readout centering is way off, then something else is wrong. As far as modifying a plug-in to substitute for the standardizer for the centering calibration, I mean the signals on pins A11 and B11 from the plug-in into oscilloscope backplane. When adjusting the trace centering, the standardizer plug-in is set to leave the differential signal pins open. With some plug-ins, this is easy to do. On a 7A16A or 7A26, you can remove Q820 and Q840 which at least on mine are in sockets. That will disconnect the output when the plug-in is set to full bandwidth. On a 7A18 you can do the same thing by removing Q280 and Q380. I verified the above to work this morning. If you have a plug-in extender or you can reach the needed signals with a plug-in operating in the mainframe with the covers off, you could measure the voltage between pins A11 and B11 and set it to zero via the position control. Then use the plug-in as your calibration reference for centering and do not bump the position control. This is how I recalibrated my 7834. The voltage at the pins is 50mV per division so it is easy to measure. Incidentally on the 7603, it is much easier to calibrate the CRT trace centering since it will generate a trace with only a timebase installed. If you had one, you could calibrate the 7603, install a plug-in, center the trace with the position control, and then use the plug-in to center another oscilloscope. You could also short pins A11 and B11 together to generate a center reference. On Wed, 18 Jul 2012 22:44:25 -0000, "keithostertag" <keitho@...> wrote: David- This may be OT, but could you elaborate on your idea more? First, I don't know your references to E.1, E.2 etc. I don't see that in the Horizontal Calibration procedure. Then, when you say:
I think you can do the above without a standardizer if you zero the
differential output from a vertical amplifier which only takes a
voltmeter to do. Then use the "zero standardized" vertical amplifier
in the horizontal slots when the standardizer is called for and do not
fiddle with the position control. Alternatively I think temporarily
shorting the two differential output pins on the vertical amplifier
plug-in together would work also. I don't understand this at all. The vertical amp plugins I have, 7A18 and 7A26, don't have any outputs. Do you mean somehow tap into the circuitry? Do you mean short the backplane pins?
This likely has little to do with the original topic (positioning the Readout), but it's a teaching/learning moment :-)
Thanks,
Keith Ostertag
|
Re: How to adjust horizontal position of Readout display? R7903
Thanks David and Magnus for these details- more for me to study and learn.
Here is a photo better showing the problem.
I have loaded the R7903 with plugins with no inputs just to show the readouts. You can see that they are a little too far to the right, which was my original topic. All the characters seem to be displaying correctly.
However, only yesterday (after I started the thread) I noticed that channel 2 right vertical doesn't display the readout (as you can see in the photo). So now I am wondering if there might be a connection between the two issues, maybe not.
My 7A18's have option 6, so they don't have the "Identify" feature. The only vertical amp I have with "Identify" is my one 7A26. I also have a 7B53A loaded just to show that both channel readouts do display for all other slots. The 7A26 displays readout in channel 1 & 2 in the left vertical as expected, so it is not a plugin issue.
If I push the Identify button on the 7A26 I do get both the "Identify" word and the trace moving up a bit, except for channel 2 right vertical. For channel 2 right vertical I do get the trace moving in response to pushing the Identify button, just not the word.
I have been studying the manual, but it's kinda like trying to learn Linux in one day...
So far I have checked the following by swapping with known good chips from my 7844:
U2232 (replacement)
U2250
U2155
U2250 and U2260
U2284
From my reading those would be the most likely IC chips to cause this type of problem (easiest things to check first).
Your thoughts?
Thanks,
Keith Ostertag
toggle quoted message
Show quoted text
--- In TekScopes@..., "magnustoelle" <magnustoelle@...> wrote:
Hello Keith
on your return question:
I don't understand this at all. The vertical amp plugins I have, 7A18 and 7A26, don't have any outputs. Do you mean somehow tap into the circuitry? Do you mean short the backplane pins?
This likely has little to do with the original topic (positioning the Readout), but it's a teaching/learning moment :-)
Thanks,
Keith Ostertag
Yes, this refers to the circuitry.
On the 7A26, you may want to check out the output stages which Q820/Q840 and Q860/Q880 form.
See page 3-3 in the 7A26 Rev C Manual from March 1975 for a description. And refer to schematics DISPLAY SWITCHING AND OUTPUT, number 4 on page number 63.
The contacts relevant for the vertical output signals on the rear connector are A11 (positive signal) and B11 (negative, as this is a differential signal).
Good Luck,
Magnus
|
small jewel light Tek 561A
hello all,
what is please the name of the bulb in the little jewel light from Tek 561A? it is not the same then in the large 500 series scopes.?
thank you + greetings Martin
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Re: General Electronics Question
On 07/19/2012 08:08 AM, Brad Thompson wrote: On 7/19/2012 5:35 AM, Mark Wendt wrote:
<snip>
To take Rob's question a bit further, when replacing ceramic disk caps,
is there any issue using MLCC or polyester film caps? What about with
those nifty little "tube" caps Tek seemed to like using? I mean, the
ones that look like hollow resistors.
Hello, Mark and the group--
If the capacitors you're referring to look like this...
...They're 'radial-leaded tubular ceramic capacitors', or
sometimes referred to as "dogbone" capacitors. These
capacitors are often manufactured with various
capacitance-versus-temperature characteristics and are
used for frequency compensation in tuned circuits.
Here's a pointer to their color code-- scroll down the
page to "tubular ceramic":
Electronic folklore describes the tubular ceramic caps as
"highly reliable" [1], but if you need to replace one, a modern
disc-ceramic cap with the same value, tolerance, voltage rating
and temperature coefficient should do the job.
73--
Brad AA1IP
[1] While making voltage measurements on a 1950s-vintage Philips
multiband receiver, one of two tubular ceramics connected as
RF-bypass caps across the power transformer's high-voltage secondary
failed-- arcing and smoking. That's the first one I've ever witnessed
failing.
Brad, Yeah, them are the critters I was talking about. Thanks for the reference URL. Mark
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Re: General Electronics Question
On 7/19/2012 5:35 AM, Mark Wendt wrote: <snip> To take Rob's question a bit further, when replacing ceramic disk caps,
is there any issue using MLCC or polyester film caps? What about with
those nifty little "tube" caps Tek seemed to like using? I mean, the
ones that look like hollow resistors. Hello, Mark and the group-- If the capacitors you're referring to look like this... ...They're 'radial-leaded tubular ceramic capacitors', or sometimes referred to as "dogbone" capacitors. These capacitors are often manufactured with various capacitance-versus-temperature characteristics and are used for frequency compensation in tuned circuits. Here's a pointer to their color code-- scroll down the page to "tubular ceramic": Electronic folklore describes the tubular ceramic caps as "highly reliable" [1], but if you need to replace one, a modern disc-ceramic cap with the same value, tolerance, voltage rating and temperature coefficient should do the job. 73-- Brad AA1IP [1] While making voltage measurements on a 1950s-vintage Philips multiband receiver, one of two tubular ceramics connected as RF-bypass caps across the power transformer's high-voltage secondary failed-- arcing and smoking. That's the first one I've ever witnessed failing.
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Re: How to adjust horizontal position of Readout display? R7903
Hello Keith on your return question:
I don't understand this at all. The vertical amp plugins I have, 7A18 and 7A26, don't have any outputs. Do you mean somehow tap into the circuitry? Do you mean short the backplane pins?
This likely has little to do with the original topic (positioning the Readout), but it's a teaching/learning moment :-)
Thanks,
Keith Ostertag
Yes, this refers to the circuitry. On the 7A26, you may want to check out the output stages which Q820/Q840 and Q860/Q880 form. See page 3-3 in the 7A26 Rev C Manual from March 1975 for a description. And refer to schematics DISPLAY SWITCHING AND OUTPUT, number 4 on page number 63. The contacts relevant for the vertical output signals on the rear connector are A11 (positive signal) and B11 (negative, as this is a differential signal). Good Luck, Magnus
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David Hess
David C. Partridge