I have a HP-25 since 1976, during school time I really enjoyed it and sometimes wishing continuos memory, until the day it stoped working, I didn´t care because I already had a HP 41CV, and now thanks to HP FORUM, I changed the NCd batteries but it doesn´t turns on with the batteries, only with the AC adapter it turns on but the display remains flashing.



I, too, have used an HP-25 since 1976. I would sometimes get a flashing display, and it seems to have happened when the battery terminals were not making contact with the terminals in the calculator. Some NiCds that I used had flatter tips, which made it harder to make contact.

Of course, I assume you have the "S" spring is in place at the base of the batteries and that the polarity is correct.

Hope this is helpful.



First make sure that the batteries are installed in the holder properly and are connected together at the base by the spring (and also a welded strap between the two cells). The cells must be free to move and must not be glued to each other. Check that you get voltage between the two ends that connect to the calculator.

Mark sure that the battery contacts in the calculator are clean. Sand them lightly with very fine sand paper. It can also help to place a small wad of aluminium foil between each cell and the calculator battery contact.

One should NEVER connect to machine to a charger unless known good batteries are installed in the machine AND they are making good contact.


Thanks Larry and David.
I already checked the "S" spring and polarity is correct and the voltage between the two ends is 2.469 v. but I wonder what could be damage inside ? since I got a battery leakage and I never notice it until the day I changed the batteries and as David said that one should NEVER connect to machine a charger unless known good batteries are installed in the machine and I did connected it before the battery change.


Julio: The charger circuit in the HP 25 and similar models is one of its weakest features. The batteries, while accepting the charging current, also work as kind of a voltage limiter, which prevents excessive voltage to reach the delicate electronics inside. So, when batteries are not in a good working condition, or when there are false contacts between the batteries and the rest of the calculator, the voltage from the AC adapter may damage the calculator chips.

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