HP-65 more on the card reader

[wallyt]

Vbsw is the switched battery voltage (pin 18 of the 0158 sense amp). If you are using the battery for power I would assume this to be clean (unless something is getting into this). The other voltages, however, are generated from the DC-DC converter on the logic board. I would definitely scope those.

The only other thing I could say about this is that in my experience I have run into a bad mag card now and then. I would clean these with an alcohol wipe (both sides) and let it dry. Lots of oxide would come off on the wipe. They would work fine after this. But you are showing bad waveforms so I doubt this would be your problem.