Rebuilt HP 67 battery pack problems

[teenix]

I hope you are lucky if the battery was reversed and didn't turn the calculator on.

I'm not sure how the 67 CPU board will handle a reversed battery, although I think the switch mode power supply design will block any reverse voltages. The 47uF power supply bypass capacitor will have reverse battery directly across it and being a tantalum type will not like it - smoke being a telltale sign.

As Bob mentioned the sense chip seems to pass the reverse battery voltage though the Vbb pin to the motor output pin Vm (motor running backwards). Also not sure why, but hope it wasn't damaged. There is a tantalum capacitor on the motor connections, this might grumble at the reverse voltage as well.

In the battery compartment, the brass spring terminal closest to the top of the calculator is the negative terminal.

cheers

Tony