HP 67 Circuit Board

[metawops]

Thanks for all the most valuable tips, teenix! Much appreciated!

However, today let's put all things screw and silicon and pressure and gummy and that aside and focus on a new problem (yay!) I observed today: When I insert a card and the first switch (MTRS) goes down (i.e. makes contact with the pad; can hear it) the motor should start, right?

Well, it doesn't.

When I push the card a little bit further in so that I feel that it has now contact with the fuel tube I put on the axle – still no motor.
When I still push the card further in (yes, not good, I know) at some point the motor actually starts (obviously too late) and the display says "Error".

Now ... is my sense board defunct? How could I test what's going on? What could cause this behaviour?
I've got a 4 channel oscilloscope here and am ready to test ... And I'm further studying your "Classic Notes", teenix, excellent source! (I'm by no means such an electronics expert like you are and don't understand everything immediately ...)

I really hope that my sense board is okay ...