HP 67 Circuit Board

[metawops]

Thanks AndiGer, I will have a look at that HP-97 manual asap.

Meanwhile ... I took a look at the HP-67 schematics and the "Classic Notes" PDF. In a first step I wanted to see whether the first ball/switch, MTRS, that the card hits, actually does something/switches.
The process is documented on page 22 (PDF page 23) in the "Classic Notes" PDF and on the next page we see the oscilloscope diagram that includes the MTRS line.
However, I couldn't find a note where to put my probe on to get that MTRS signal so I looked into the schematics and found that pin #13 of the main logic board should be that MTRS pin, right?

Well, actually, I might be wrong here because this is what my scope says when connected to that pin and when the HP-67 is switched on (nothing else, no card action):

       

I get a ~6,6V peak every 300µs (screenshot 1). And that peak is ~5µs long (screenshot 2).
When I gently push in a card so that the first (MTRS) switch should "fire", nothing happens here.

Maybe I'm on the wrong pin?!