Alright, need some Sys3 driver board help.
I got Big Hurt back together, and all is mostly OK except for the #2 Drop Target Trip locking on. This is transistor (mosfet) Q10, a 2N10L.
I replaced Q10 with a new 2N10L a while back and tested in a working game, but still had the same problem.
Now that Big Hurt is mostly working I replaced Q10 for a second time, still have the issue. But its DMM "diode check" is consistent with other good Qs on the board. So I tested the associated resistor and cap. The resistor is fine, but the capacitor at C21, a .01uf, was giving funny readings... so I replaced it.
Still have the solenoid problem.
Looking further upsteam on the board goes to U2, the 74HCT273. Not entirely sure how to test this chip, but using a DMM with red lead on pin 10 (ground) and the black lead on the output pins... they all read the same.
But I keep going back to that weird C21 capacitor reading. It's completely out of whack to all the others. Why? What would cause this? All the other components in the circuit seem to be OK. So I must be missing something...