HP-67 Card Reader became very touchy

[teenix]

C3 delays the turning off of Q1 when the calculator is switched off. This may prevent spurious motor running with power changes. This might happen sometimes but not others, and maybe why the engineers added it. This is of course dependent on the MI input on the sense chip being for Motor Inhibit, otherwise I have no idea :-)

The ribbon cable in the image on post #44 looks like care needs to be taken when removing or inserting, being creased like that. The ribbon connectors will crack easily in this situation. They can be repaired with solder but care from then on will still be required. I haven't been able to find a suitable replacement for these. Aside from lengthwise, 0.1" pitch spacing doesn't seem to be the norm for cables like this these days.

cheers

Tony