HP 97 card reader - tantalum capacitors

[AndiGer]

Flogging a dead horse, I know ... old thread.

These days had another HP-97 on the repair desk. Didn't read any card but today I tried and it wrote the card. Successfully read in another machine.

So I found this thread and did what I had done before:
Unsoldered C4 and changed to another one with good values. C6 was ok as is the other one I still have. So resoldered original C6. The cards are read now :-).

I checked Vss and Vgg. IIRC Vgg before changing C4 was -11.25V, now is -11.50V. Maybe that was the culprit? Design voltage according to the service manual is -12.00V.
Vss before and after change of C4 = +6.08V (design +6.25V).