Capacitor lifetimes


Does anyone know if HP utilised discrete capacitors with known lifetime issues?

Thanks, David


The one capacitor that almost always causes problems is the small blue dipped tantalum bypass capacitor in HP67 card readers (also some '65 readers). If your reader writes but won't read, this beastie is the problem. It will look and test good, but it develops a high internal ESR (equivalent series resistance) and stops doing its thing. When rebuilding a reader in these machines, I always replace this cap even if it seems OK. Eventually it won't be.

I have also seen bad tantalum power supply filter caps in Woodstock series machine power supplies (particularly HP29C units).

Very occasionally the main power cap in an HP41 will develop a leak and drain your batteries quickly.


David Smith:

Regarding the HP-67:
Are you referring to the small capcitor which is attached
to the terminals on the motor itself? Thanks.



No, the problem bugger is on the little reader circuit board. There are three tantalum caps there. Two are used in connection with the head windings and the other is the failing power cap. Also the HP97 reader can have the same problem (but not nearly as often as the '67)

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