Before I start tearing down the CPU board and isolating components, I wanted to check here to see if anyone had experienced these symptoms or had a theory about the issue.

The Hook I have came to me with several issues, many of which I'm convinced that the previous tech caused. I've been undoing his "work" with good success (He had replaced some PNP transistors with NPN versions). And I backed off the PSU HV drive voltage mods back to factory (which incidentally made me discover the display is actually in great condition when not overdriven).

The remaining issue is that upon starting the game, it thinks some switches have been pressed and goes a bit crazy. The far right pop bumper randomly pops and I get clocks triggered a lot and occasionally "I lost my marbles". The switch test shows no issues, it only seems to be once the game has started and the coils have been energized.

Poking around on CN-10 is interesting. While all pins are around 5v, the far right pin (pin 1 #8) is reading 35-38v when a game is playing, but 5v when it is not. This leads me to believe there's a short somewhere between the coil drive and switch returns, but it's not obvious from the circuit diagram how this is happening.

Does anyone know what's going on?

Answering my own question here, but leaving this up because it may of use to someone in the future.

Surprisingly, it wasn't the previous tech's fault this time, instead it was caused by a flash lamp touching one of the lugs of the microswitch on the power scoop. The flash lamps are powered at around 34v and seem to be switched to ground, which meant I was getting a full 35v on the white/gray wire of the switch matrix (through the diode on the switch).

No phantom weirdness going off anymore and on to the next problem which is an issue with the green/yellow wire (I know this one has a service bulletin about getting crushed, but it looks okay visually. Hopefully I can buzz out the problem with that one pretty easily.

bad_lamp (resized).jpg

green-yel (resized).jpg

Answering myself again...

The switch problem turned out to be a bad transistor on the switch driver side (I was seeing 3.1v where there should be 5v). I thought I'd already replaced this transistor, but it may have blown again before I was able to fix the lamp flasher touching the return line problem.

Anyway, everything seems to be working now and I'm happy I didn't need to replace the PIA (although I have a spare now).

On to the teardown and cleaning for the new rubber kit. This game is filthy with a lot of blackened soot underneath around the coils and moving parts.