HP-67 Charge Issues

[GreyUser]

Stop using the charger immediately, it could damage the calculator. The 400uf filter capacitor has failed and is allowing ac ripple on the dc supply. Replace with a 470uf 16 volt device as you’ll never find 400uf and it’s not critical, capacitor tolerances are quite large.

If your charger has a voltage selection switch, be careful upon re-assembly. The switch contacts must be oriented in the same direction to prevent damage, the contacts small pin goes in the hole which is only on one end. It will make sense when you look at the bits when it’s open…

IIRC the charger schematic (in ascii art) is in the archives courtesy of Tony Duell.

Edit: link added. https://www.hpmuseum.org/cgi-sys/cgiwrap...i?read=390