HP 25 low battery indication at 2.6 v

[Peter Klein]

No joy, unfortunately. I hooked the HP-25 up to an adjustable bench power supply, whose accuracy I verified with a DVM. I adjusted the pot to a number of positions along its arc. Once I began adjusting it, the low battery indicator stayed on at all voltages between 3.3 and 1.8.v. Lower than 1.8v and it shuts off. I cycled power on off and on after each adjustment.

In each case, the result was the same: Power on. Calculator displayed opening message. I keyed in the digit “1” and pressed Enter. The low battery indicator came on. This was unaffected by the number of digits displayed.

I also reflowed the solder points of the pot and nearby pins of the cathode driver. And I checked for solder bridges with a magnifier. No help. Current drain appears to be about right. I suspect the pot has failed internally.

So I’ve turned the low battery indicator off using Bernhard’s flag. Unless someone has other ideas, I guess I’ll rely on the operating time function and/or periodic battery checks.