HP35 problem with a calculator, maybe due to a faulty charger

[Maximilian Hohmann]

Hello1

(03-20-2021 01:45 PM)aurelio Wrote:  The calculator turns on (with a charge battery pack), but shows erratic behavior by showing meaningless numbers on the display. any idea what might have been damaged

Before trying anything else I would connect a laboratory power supply set at something between 3.6 and 4 volts to the battery contacts directly (carefully watching the polarity). If it still behaves strangely you can start troubleshooting. With old battery packs you never know: It could be contact problems or a dying battery cell.

Good luck
Max

NB: And your story is yet another reminder to never run these old calculators from a wall charger, even the models which have some degree of overvoltage protection like the HP-35. I put all my chargers in a big box long time ago (with a little label on each of them showing the serial number of the calculator it belongs to) and run the calculators either from a laboratory power supply or externally charged batteries.