465B recapping and tantalum caps


pdxareaid
 

Greetings 465/465B repairers and recappers.
I have just spent time with a couple of broken 465B's and thought I'd pass along the experience.

1. Recapping low PS
I recapped the low power supplies and used the ebay discs to install snap-in caps. https://www.ebay.com/itm/273254508468
I now regret having used those discs.
After I ordered the discs, I noticed a TekScopes member "n4buq" had a much better solution (bravo!) and may still in fact
offer his standoff board for sale. If not, it could be made with a low tech copper-clad hole board, resist pen and etch acid.
With that solution, everything is easily accessible.
I did, in fact, break one trace, not discovering it until after the new discs/caps were installed.
Even though I did a continuity check to avoid exactly this, I think I damaged the trace when doing some minor work nearby just before cap installation.
I had to jump the trace off the board for a fix. I could have easily fixed it on the A4 board if I had used his standoff board solution.
n4buq writeup https://groups.io/g/TekScopes/files/Replacing%20Electrolytic%20Filter%20Capacitors%20in%20a%20Tektronix%20465.pdf

2. Tantalum Caps
Years ago I put together an HTML file identifying the dipped tantalum caps that tend to fail so often.
I lost access to it in the Yahoo/GroupsIO move but that has been fixed recently.
I have uploaded an updated HTML file with the following addition (as well as updated contact info):
C4331 47uF 20V with a note. It is a confusing one. Should it be a tant or a film cap? Read the note.
The file is https://groups.io/g/TekScopes/files/465Btants.html

3. Mysterious Cap
While I was scratching my head over 2. above, I notice a tiny dipped tant on all three of my (early build) A4 boards. I had missed it in the original
survey. I tried to look it up in the manual (ARTEK early build 465B) but it is not there. The pads are there but the tant does not show up.
I looked for an add/delete change in the manual but did not see any appropriate.
I think it is a filter cap in the horizonal amplifier circuitry but it is not in the diagram either.
It physically sits between R4373 and R4374 on the A4 board. The pads are even on the manual's A4 diagram, but no cap.
If that thing shorts, it is going to be one confusing debug.
Here is a pic of it https://groups.io/g/TekScopes/photo/269282/3324900
Does anyone know what is going on here? Can anyone identify this cap and point to Tek documentation?

Join TekScopes@groups.io to automatically receive all group messages.