HP 29 & 21

[teenix]

(11-14-2022 06:27 AM)zixingcheche Wrote:  Hi all

I exchanged the ACT. now, HP29C is with the one from HP21's.
the symptom is still keeping "0", and the keybroad doesn't work. but the on off switch works.
It seems there are other parts are not working well in side HP29C.

any advise? thanks!

It appears you may have a faulty ROM and/or RAM IC.

I tried running my 29C emulator and alternately failing each ROM and RAM but I could not recreate the faulty display you have. This doesn't really much as one or more of the 65,536 ROM locations, if faulty, could output any value between $000 and $3FF.

The only real way to test is with an oscilloscope to track the Is and DATA buses.

cheers

Tony