Help repairing a Tektronix 2465B A5 board

[car46999]

Hello all,

I attempted to replace the leaking capacitors on my A5 board and ended up with an A5 that no longer worked and 3 solder pads that came off the board. The scope worked prior to my botched repair.

Using a resistor lead I was able to solder the lower connection point of C2890 to the positive side of C2965 (negative connection point for C2965 still had a solder pad at this time) and finally to U2890 pin 14.
With the identified capacitors connected as stated the scope would not function. It would power on, the lights for each channel illuminated sequentially, the rest of the panel lights lit up, but there was no trace, or text on the display. No trace when beam find was depressed. I messed with all the focus and

Questions I hope to get answered:

Did I connect the above components correctly (in the attached photo I circled how the connection points ohmed out)? If this is incorrect where should they connect to?
What vcc should I see at pin 14?

I also replaced C2011, C2113, C2331, C2520, C2222, and R2016. These all went okay, I have double checked that none are shorted and that they ohm out okay to their connection points. I used the OEM values, same as what I removed.


Thanks for any help on this, I am pretty bummed that I botched this repair.

[lordvader88]

I'd say don't worry about the pads/physical/mechanical problems, at least 1980s tech is not all SMD fine pitch.

I have a Tek2430A, just ordered a 2nd CCD hybrid chip, both where bad when I got it used, didn't even realize for ages, or they failed after??? That's my 1st scope.

What went wrong and made u re-cap the A5 broad ?

[car46999]

Lordvader88,
The electrolytic capacitors were leaking, causing damage to the board. I also believe it was causing the jitters that I was seeing in the text on the display.

To add to my original post, for informational purposes:

Here are the components I used:
C2011 and C2965
293D336X9010C2TE3
Desc.:    Tantalum Capacitors - Solid SMD Tantalum Capacitors - Solid SMD 33uF 10volts 10% C case Molded

C2890, C2520, C2222
C1206C104J1RACTU
Desc.:    Multilayer Ceramic Capacitors MLCC - SMD/SMT Multilayer Ceramic Capacitors MLCC - SMD/SMT 100volts 0.1uF X7R 5%

C2331 and C2113
293D106X9035C2TE3
Desc.:    Tantalum Capacitors - Solid SMD Tantalum Capacitors - Solid SMD 10uF 35volts 10% C case Molded

R2016
RN732BTTD1001F25
Desc.:    Thin Film Resistors - SMD Thin Film Resistors - SMD 1kOhm,1206,1%,25ppm, 125mW,150V

[tautech]

Regardless of the new caps you've installed do the voltage rails measure as correct to specs ?

Some possible errors:
Cap installed reverse polarity ? (quite possible with SMD)
PCB overlay indicates one polarity and really it's the other way around. (not uncommon)
Lifted pad and therefore broken connection to through hole plating ?
Microscopic break in a trace ? (check continuity)

[Chris56000]

Hi!

It might not be necessary to worry about the lifted pads – you might be able to solder a conventional tantalum bead electrolytic in the holes for the bias either side of the pads, otherwise, if the bias are too small, you could solder very fine tinned copper wire to the vias, then resolder the leads to the tabs of new surface–mount tantalum capacitors.

The ideal solution is those replacement stick–on self–adhesive copper pads sold for PCB repair. but there seems to be no convenient means of ordering them online anymore – even AliExpress and Bangood don't advertise 'em!

Chris Williams

[car46999]

Update, I checked continuity of all the components I replaced and checked the schematic to see the purpose of C2965 and C2890 (the two caps that are still off the board).
Best I can tell they are filtering caps, so I risked it and powered the scope up to check voltages. ( I am going to order leaded capacitors to replace the surface mounts) I am pretty confident these capacitors are not the cause of my issue.

I checked the following voltages, all checked okay:
+5v on pin 14 of 74HCT00 chips
+5v on C2965 and C2890 (these were part of the replacement)
+15v on C2331 and C2222 (these were part of the replacement)
-15v on C2113 and C2520 (these were part of the replacement)
+10v on R2016 (part of replacement)

All voltages test okay on the J119 test header.

Power on bit stops with the ADD LED illuminated. This time I did see a faint trace, I adjusted the grid bias up and the display appeared (display is not normal, but it is there).

From there I ran the built in self test it fails Test 05 fail 44. Prior to the capacitor replacement it did not fail any tests.

I also ran exercise 02, values were displayed for each of the positions leading me to think the calibration is still good.


I have searched Test 05 fail 44, and the only thing I found is that people replaced the A5 and the problem was fixed.
Any ideas?

[car46999]

I got the leaded capacitors in today along with the replacement resistors for R2012 and R2014 (I replaced these because I removed them to check their resistance values, I do not believe they were bad). Installed them with no issues, I was able to use the "negative" solder pad for C2890 and pin 14 on U2890 for the positive lead of C2965. I piggy backed C2890 on it's leads.

The actual issue causing my failure was that pins 16-20 of U2101 had cold solder joints, likely from the hot air gun I used to remove the original leaking capacitors. After I re-flowed them, I was able to adjust the grid bias back down and and no more Test 05 fail 44.

New issue that I need help with:
When I move the trace up or down the text display starts jittering (this issue was present prior to the capacitor replacement, I hoped it would fix it).
It is worse if more than one trace in on. Also with all the traces on the traces start jittering.

Here is a video of the issue, it might be hard to see, but it is there.

https://youtu.be/7etE-qff1VU

[car46999]

I am going to go back and check the voltages again, and see if they become unstable when the jitter occurs. I also did not check the ripple, I will do that.

This has not had the power supply caps replaced.

[tautech]

I got the leaded capacitors in today along with the replacement resistors for R2012 and R2014 (I replaced these because I removed them to check their resistance values, I do not believe they were bad). Installed them with no issues, I was able to use the "negative" solder pad for C2890 and pin 14 on U2890 for the positive lead of C2965. I piggy backed C2890 on it's leads.

The actual issue causing my failure was that pins 16-20 of U2101 had cold solder joints, likely from the hot air gun I used to remove the original leaking capacitors. After I re-flowed them, I was able to adjust the grid bias back down and and no more Test 05 fail 44.

New issue that I need help with:
When I move the trace up or down the text display starts jittering (this issue was present prior to the capacitor replacement, I hoped it would fix it).
It is worse if more than one trace in on. Also with all the traces on the traces start jittering.

Here is a video of the issue, it might be hard to see, but it is there.

It's quite visible but because there's no signal present IMO you're wrong to call it jitter.
Instead it's a display flicker. 

Rework back through the excellent Tek manuals and maybe this one can help too:
http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf

[MarkL]

I am going to go back and check the voltages again, and see if they become unstable when the jitter occurs. I also did not check the ripple, I will do that.

This has not had the power supply caps replaced.

Yes, definitely check the power supply ripple first.

There are adjustments to tweak the vertical and horizontal readout jitter, R805 and R618.  They are described in the service manual in the "DC Balance, And X-Y Phase Differential" section (page 5-25 in publication #070-6863-01).

Your symptoms look a little unusual, but you should give the adjustments a try.  Mark the pot positions with a fine Sharpie before you move them.  If they don't help, put them back to their original positions.

[Tektron]

Excuse my English. Translation from Google.
car46999, I did not find in your messages mention of cleaning the board from electrolyte.
Electrolyte has a very high wettability and "creep". Because A5 is located on the side wall of the device, the electrolyte flows down and spreads to the sides. can swoop under the housing SMD chips and other parts.
You can not wash this unit by immersion in a bath. You need to use a piece of cotton wool soaked in ethyl alcohol.
Preliminary inspect the block with a magnifying glass and determine how much the electrolyte has grown. Clean only the spreading zone. If necessary, it is necessary to evaporate and clean the chips, clean the surfaces below them. then solder everything to its original location.
Below is a photo of my A5 block before repair.
If cleaning has already been done, do not take my message into account.