What's wrong with my HP25?

[Karen]

I have two HP25s "inherited" from my father. One of them does not work. The fault is nothing to do with the batteries, because I know the battery pack is okay from testing it with the other calculator (which works fine). If you put a decent battery pack in the dodgy model there is no response when you turn the thing on.

I also have two mains adaptors that came with the calculators, but I don't know if they work or not. If you plug one of the mains adaptors into the dodgy calculator, you get an "8" on the right hand side of the display and various flashing LED elements. Plug in the other adaptor and there is no response at all.

So, could anybody give me any help/advice on this problem...?

Thanks, Karen

[Jan]

Hi Karen

Sounds like a wiring or contact problem, maybe in the on/off switch. I would switch the calc of, assure it is in run mode 1st, install the batteries and then switch it on. When there is no response GENTLY push on the on/off switch from above and see if that helps. With my 34C it usually does and although it is from a different model series there could be some similarity to the 25 in this respect.

good luck
Jan

[Randy]

That behaviour is usually indicative of a damaged ACT chip or possibly a bad rom. Flashing zeros is another symptom.

The IC's in a 20 series unit get fried when connected to the charger without a good battery in place as the internal voltage reaches about 8 volts DC without a load instead of the proper 2.5 to 3. The only source for the the ACT IC is from another 20 series unit. The 27 is not compatible.

The golden rule to preserve your 25's: *Never* connect a charger to a 20 series unit without a good battery installed that is making proper contact. Since it is not always possible to know the conditions and connections, it is safer to power with alkalines or batteries charged externally from the unit.