HP-67 - 1612A03018 - Card Reader Advice Requested (was HP-67 - strange behavior)

[teenix]

(09-16-2019 06:54 PM)albertofenini Wrote:  or, and this is even stranger , if we press ANY key prior to turn it on and we keep it pressed we get :
a steady 0.00 but with the key pressed the rest of the keyboard is non functional,
if we release the key than everything shuts off again.

Thanks again to everyone for helping us out !

The microcode executes exactly the same up until the point where the keyboard is tested, whether a key is pressed or not.

If a key is down at this point, the code will stay in a small loop until the key is released, then it will sit in the main loop waiting for a key press, card insertion, or PGM/RUN switch change.

If no key is pressed at the mentioned point, the main loop executes.

During the main loop, I tried to force the code to branch to other code sections but it did not result in a blank display.

Hard to say but sounds like a ROM issue which may cause a code failure after the mentioned point. The ROM addresses for the main loop are below 256, so the first ROM may have a failure.

cheers

Tony