Long story short, I melted the knocker on a 1979 SS Bally Paragon when it first powered up. I don't want to continue until I know more about what happened.

When I turned it on for the first time with the Solenoid Driver Board hooked up, the knocker fired when I flipped the switch. It scared us out of our shorts cause we thought it exploded but it was just the knocker and it seemed fine after that so I assumed that it was supposed to happen. I also had the GI hooked up to the rectifier board so we had some lights. We were looking at everything and still laughing about the jump scare until about 10 seconds of having power, we smelled the acrid smoke and turned it off.

We found that the knocker was smoking out of what looked like one of the terminals but the paper had gone blistered and black and the sleeve melted and fused the rod in place so it was coming from the coil itself. It fused in the relaxed position so I don't believe it was on the whole time...or was it? Either way the knocker's dead.

1)What would make that happen? A coil burning up?
2)Why did the knocker fire when switched on?
3)Is it a stuck switch on the board or a wiring short?
4)Was the knocker bad?
5)Will I just melt a new one?
6)What's the appropriate "pre-knocker" test?
7)Can I skip the knocker since I'm going freeplay? Is it safe this way?
8)Is the knocker even the problem or is it higher up?

The playfield 1A fuse was removed due to a busted clip. I would of pulled the fuse to test the board first anyway. Is that wise? I have a replacement clip but I'm weary of sending untested, coil melting, power down to the actual playfield if there's a problem higher up the chain.

I picked up the Paragon a week ago which was missing the MPU board and had reported issues with the rectifier and Solenoid Driver Boards. I repaired those issues and am reading voltages correctly at the test points on both boards. The Lamp and Sound driver boards are present in the machine but unhooked to anything at all. The MPU is a new Alltek in the static bag next to the machine waiting to be installed in to a safe machien.

I'm curious as to what happened. We clipped the knocker and taped off the leads and the machine is seemingly stable. We still see good volts on all TPs on both rectifier and SDB. Is there something else I should check?

As for the repairs:

Rectifier Board:
I had a bad rectifier and fuse clip. I replaced all the rectifiers with 35A ones. I also replaced the one corroded fuse clip and the J2 bank of male connectors as there was some corrosion on the pins. I ran through all of the test points with power applied and they're good. I did this with no other boards connected.

Solenoid Driver Board:
There was a couple of traces that had lifted off the back of the board entirely. I clipped those off and wire bridged them. Another pad had lifted and broken free of the trace so I ran some solder down the trace. After the repairs, all test points are good with power.

I'm brand new to pinball repair but I'm learning a lot. I'm hoping frying this thing teaches me something. I appreciate any and all help and advice you all can give. Thanks.

Well, I found out that the transistor for the knocker was shorted, which is also the same spot the trace broke and I had repaired. I lived and learned. I learned to test down the line further before assuming my repairs are good. I could of seen it was shorted before applying power. Parts are on the way and I have to live without a knocker for a bit.