HP-10 disassembly/reassembly

[teenix]

(02-16-2020 02:53 AM)[kby] Wrote:  Tony,
Thanks for the corrections. It now agrees with at least the part I was looking at and helped me to realize that indeed the K12 pin is connected to the display.

Which leads me to a follow-on question. I'm not sure how the entities are defined in your explanation. The basic question is, if, indeed as is surmised CPU pin 36 is dead and unresponsive to keypresses, should there also be some kind of display artifact as well? Can you give me a better idea of what specific (kind of) artifact I should be looking for? I don't see anything obvious, but maybe I'm just not looking carefully enough at the right time.-kby

I was alluding to an electrical fault on the PCB between the keyboard and CPU pin. It is possible that if all 8's were displayed that the corresponding digit might look slightly dimmer or brighter - hard to say.

A scope attached would at least verify that the correct signal is present. Hopefully not, but you might well see the correct signals getting to the CPU pin, but the CPU may not be interpreting it properly. Maybe the K12 line is driving the display but not LO enough to be detected as a key press. All just guesses of course :-)

The display on HP calcs flickers off briefly while the key press is processed by the CPU. Does this happen on the HP-10, and also the keys in question?

cheers

Tony