Ok, I’ve got a Paragon that was acting up on me. I seem to have fixed it by replacing the solenoid driver board, but I’m still not clear as to what was going on with the old one. Here’s the situation:

My coin lockout and flipper relay were chattering. I poked around a little bit and decided to reflow the solder on the J4 connectors and repin them as well. While this seemed to fix the chattering, it uncovered a new problem – the drop target bank (not the inline) would no longer reset. (side question – why is the drop target reset considered a ‘continuous’ coil?)

I checked the coil – there was voltage there. I grounded the tab of the drive transistor – it fired. I worked my way back, testing the circuit. It all worked good until I got past the 330ohm resistors between the PIA and the connector on the MPU board. I could ground the resistor on the connector side, and the coil would fire fine. But if I grounded it on the PIA side, the coil did nothing. I even put my scope on the connector side of the resistor, and it didn’t budge when I grounded the other side. This made me scratch my head. I tested this another Bally game of the same era, and it worked as expected.

I even tried the “hack” that @barakandi showed to replace part of the CA3081 with a discreet transistor, but that made no difference.
But then I swapped out the Solenoid Driver Board, and all is good again.

Can anyone help me understand what is wrong with my original SDB? What would cause it to basically “ignore” a low output from the PIA to fire this coil?

Yeah, I thought that too. It measured fine and I swapped it with the unused one next to it.
No luck.