HP Forums

Full Version: HP 25 schematics? IC pinouts?
You're currently viewing a stripped down version of our content. View the full version with proper formatting.


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,


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.