Yes IC17, It just seemed strange to get a constant 5V on those outputs when it was part of the tape circuit.
And I have seen the pots track on all the 4051 outputs EXCEPT pin 1 on IC18, That sits at a constant 4.9V
But I will replace both 18 and 19 and use machined sockets.
And yes, using the x10 setting on the probe.
Understood about the scaling.
What you describe about missing bits sounds like what is happening. This is what seems to set the synth off, and scramble all the data in a patch. You can watch the program and bank buttons change when that happens, as well as the write and manual buttons, and see it on the scope from TP2 as well.
And I'm loathe to admit I have not been able to figure out what "ST" is or does, but I'd be glad to check it if you can tell me what switches it.
Thx.