HP Forum Archive 18

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HP 25 schematics? IC pinouts? Message #1 Posted by Borja on 29 Aug 2008, 12:17 p.m. Hello, I'm trying to fix a broken HP25. When I turn it on, the display shows all 0's. It has some apparently minor damage PCB damage from a leak, fortunately not reaching the ICs at least. Does anyone have a schematic or at least some of the IC pinouts so that I can check if clock frequencies are where they should be, etc? Thanks in advance, Borja.

Re: HP 25 schematics? IC pinouts? Message #2 Posted by Randy Sloyer on 29 Aug 2008, 4:55 p.m., in response to message #1 by Borja I wouldn't be too optimistic it can be repaired... I've seen a lot of them in that state and 99% of the time it is a chip failure. You should have a ~700khz semi-sine wave on pins 13 and 14 of the ACT IC, the 22 pin package. If you don't the chip is dead. If the clock is running, look for a +5/-12 175khz system clock on pins 16 and 17. It might be a bad rom (1818-0154) but I think you'll find the ACT is the problem. The only source will be from another 25. Some others from the 20 series may work but it's not a sure thing.

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