HP-41C Shows 12 Commas, Otherwise Unresponsive

[Diego Diaz]

Hi, Good Hi-res picture indeed!

As Burkhard pointed out, those nuts are far less prone to cause the "cracked post" syndrome. So this may not be the cause of your display problem.

First I'd short the capacitor (the "SPRAGUE +" labelled cylinder) terminals for a few seconds, just to make sure that there's no remaining charge that can keep the processor into an "undefined status".

If this doesn't help. Nuts can be removed using a 1/4" (or 6.5mm) socket wrench.

Cleaning the contacts with a Q-tip and isopropyl alcohol is always a good idea and won't hurt anything. Though I'm not very confident it can make a difference in this case.

Next step in diagnosing the fault would be CPU board replacement. Do you have any other HP-41 (fullnut type) available? If so, you can swap the CPU boards (C, CV or CX) and see whether the problem persists or not.

These are great machines but somehow fragile. Extreme handling care is highly advisable.

Keep us posted.

Diego.