HP-67 Card Reader became very touchy

[John Garza (3665)]

(09-30-2023 11:15 AM)Alevin Wrote:  Being tantalum caps known to be robust and eternal...

Perhaps you are thinking of ceramic disc capacitors? They have the lowest failure rate.

But you are correct, over-voltage will lead to their demise. Along with high temperature and humidity.

It's common to blow tantalum caps in old S-100 computers (Altair/IMSAI/etc.) upon startup after years of storage. One of the many reasons to use a variac and slowly ramp up the voltage. Accumulated humidity seeping in over the years and all those up/down temperature cycles weakens the structure and dielectric material. Even with an uneventful startup, their time is limited. It's best to just re-cap all of them as they will eventually fail. This preventive maintenance gives the circuit a few more decades of reliable service.

Also good to store the unused units in a temperature and humidity controlled environment. My preferred storage method is 4mil resealable anti-static bags squeezed flat to remove most of the air.

-J