HP80 battery pack voltage reversed

[PANAMATIK]

(11-03-2016 01:31 PM)elgin113 Wrote:  ... The pack has just below 4 volts dc and just plugged the battery in and didn't power on. I also tried 3 aa batteries and still no power.

Be sure, that the two outer pins of the charge connector are connected by the small metal piece inside, when the charger is not plugged in. If they are connected and the calculator doesn't power up with the batteries, then the internal power supply of the calculator has got damage.

See HP calculator power supplies for more information. HP-80 schematic should be similar to HP-35.

The measured 16V at the charger are normal, because it is a constant current source and the voltage will go down, when charge current flows. The 4.5 V is the constant voltage for the calculator during charging.

If only the power supply is damaged then the transistors and diodes can be repaired, because replacement components are available today like 2N3904 for Q2 or BC337.

Bernhard