HP Forum Archive 05

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HP-22 Repair Message #1 Posted by D. Banks on 28 Mar 2001, 9:25 a.m. Ok, so I've got two broken HP-22s. One just doesn't power up, due to what appears to be damage to the etches on the PC board from battery corrosion. The other powers up, but half its ram is bad - stack and basic 4-functions work, but any use of the storage registers (which means, any use of the financial functions) result in stuck bits an poor calculations. I'm thinking it might be possible to build one working 22 out of these pieces. Seems like the simplest notion would be to transfer the chip containing the register RAM from the etch damaged unit to the RAM damaged unit, but that could just be naive on my part. The big thing stopping me from doing this is that I don't really know which chip is which. Suggestions?

Re: What I would do first Message #2 Posted by Mike on 28 Mar 2001, 4:56 p.m., in response to message #1 by D. Banks What I would do first is to try and get the one that does not power up, to work, if posible. If you try to get one working from two bad ones, you might wind up putting good chips into a bad caluclator. Second, damage to circuit traces does not stop the calculator from working unless they are completely disconnected. If they are simply discolored or partially damaged, that is probably not the problem. Third, I would disassemble and clean each of the contacts in the connecitons between boards and at the LEDs. I have restored operation to bad calculators by simply doing this cleanup task. Once you have one working, then swapping things to make one better one might be more realistic.

Re: What I would do first Message #3 Posted by D. Banks on 28 Mar 2001, 9:25 p.m., in response to message #2 by Mike I tried cleaning the main power etch on the one calc. It looks like it was completely eaten away. I figure I'll try jumpering around the bad part and see what happens.

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