HP-10 disassembly/reassembly

[[kby]]

Tony,

Thanks for the bad news :-(. Seriously, I do appreciate the hints and the verification of my logic. Clearly I would hope it's not the CPU as it is made of (as is said in the classic audio electronics sphere) "unobtainium." But if it is, it is.

I did think of putting a scope on the pin so I also appreciate knowing what to look for. My main issue with actually doing that is how to connect the 'scope with the calculator all buttoned up. I have since figured the only way is to run some leads from the relevant pieces out to hook up the scope. That's not great but the only other alternative seems to be making an equivalent cabled connector to attach the keyboard to the CPU without the machine being put together. Both seem like too high risk for me for a low chance of finding out something that I'm not going to be able to fix anyway.

I did get the idea that maybe I can try cleaning under the CPU chip (without removing it) in case something is parasitically draining off the signal transition. I will likely try that.

I do have a question on your schematic, though, which you gave me an implied answer to in your response, but which leads me to another question. The pins on the keyboard module (other than Vcc and the battery voltages) are numbered, but don't show where they are connected to anywhere else. Your response implied that they connect such that connection "n" connects to the CPU on the pin labelled "Kn." But it also appears there are Kn connections with overlapping values of n to the display. Is that correct, and, if so, why are the display keyboard and CPU connected on the same pins of the CPU?

Thanks again.