HP 65 with capacitor wired to battery terminals - why?

[teenix]

(07-20-2021 08:17 PM)jonese Wrote:  For the HP-65, I can only imagine it was used to carry the current spikes from the motor while it ran on the AC power pack. Similar to the HP-97 needing a battery for proper printer operation.

Dunno about the HP-35.

The original AC charger would not run the card motor by itself and needed a charged battery. Same deal for the 97 and as mentioned its printer.

The motor is not driven by PWM for speed control and has filtering, so is not noisy enough (in normal operation) to cause problems.

I cannot see a valid reason to have the cap like that unless the owner had a simple rectified AC supply powering the calculator. It would appear batteries weren't used so this setup could be damaging, although I believe the calculator is actually working.

Hopefully the displaced battery contacts have not broken away from the mounts under the case.

cheers

Tony