Classic (HP-67) charger / battery problem

[Johnboy]

(04-20-2023 01:44 AM)teenix Wrote:  If you look under the calculator, the 3 charger terminals should be obvious and arranged in a triangular shape.

With the calculator upside down and looking top to bottom, the left pin is direct to battery +ve and is where the charger connects to do its work, the middle (closest to top) pin is battery -ve and the right pin is for calculator power via the power switch.

You should also see a shorting link between the lower left and right terminals, this connects the battery +ve to the power switch when the charger is not connected.

This connection is broken when the charger is plugged in. In this state, the battery is disconnected from the calculator and is charged via the left pin. The charger also powers the calculator via the right pin when it is switched on and the middle pin connects the charger -ve to the battery/calculator -ve.

The schematic (from Tony Duell) can be downloaded in PDF format from here

cheers

Tony

Yep the charger I was using has 0 volts on the charging pin, so found a couple of other chargers and all good now.

Cheers,
John