Recently aquired a HP-25 programmable calculator (1975) that had dead
batteries and wouldn't power up correctly. Sometimes the display
indicated 12 zeros and other times the display was blank and a few
keys would indicate a single "0" in various places.

I took the thing apart. cleaned the board and keyboard with alcohol
and toothbrush and contact cleaner and managed to get it working for a
couple hours using a couple alkaline AA batteries.

Put it all back together and everything seemed to work right but the
next day it went back to the original erratic operation. I read an
article indicating possible noise problems on the data line that was
fixed with a 20k resistor termination on some particular line. I tried
that idea on a few pins without sucess and cannot get the thing to
power up with further cleaning. Haven't looked at the clock signals on
a scope yet. Hard to find a schematic for old HP calculators.

Any ideas?

-Bill