I'm restoring a Williams Star Trek: The Next Generation and when I started working on this game, a lot of the lights were out, especially in the backbox, and J120 pins 2 and 3 and J121 pins 5 and 6 were burnt. The connector for J120 was entirely bad so I replaced it, and I inspected the solder side of the driver board and reflowed these pins. I replaced all the lamps with LED, including flashers, and replaced a couple bad sockets. Nothing too unusual here.

When I finished the work and ran through tests, it became apparent that none of the flashers work (yes I have the coin door closed for flasher tests). I started diagnosing the driver board to see what the problem was, as I figured it must be something affecting the 20VDC to impact *all* flashers as that was the only commonality. LED 5 on the board is *off* indicating there is no 20VDC, and LEDs 2 and 3 are *on* indicating a low voltage issue. I next tested fuse F111 and it is good. Following that, I tested BR4 in situ and it also tests good. I reflowed the pins on BR4 for good measure. All solenoids are working. Confusingly, both cannon motors are also working, which based on what I've been reading should not be the case if the flashers are out due to a 20VDC issue.

When I have the game powered on, there is the very faint fishy smell of melting insulation from the back of the game somewhere, even with the coin door open to disable the high voltage. I have frustratingly not been able to track down the source of this smell, but my hopes are it resolves with whatever the flasher issue is. I have been turning the game on sparingly.

This is my first WPC game. What would you look at next in this scenario?

Yeah that did it. It was a bad connector on the interlock switch. I just repaired it and I've got flashers back now and LED 5 is lit. Man the flashers look great in this game too.

I still have that unidentified fishy smell and it's worse with the 20VDC enabled now. It's definitely coming from somewhere in the cabinet as I don't smell it at all in the backbox and almost not at all with the playfield down. Any thoughts on this?

Yes, good advice. I discovered that in my reading as well, and that was the first thing I did after I got it home.

I did some more digging and discovered the smell was definitely coming through the openings to the trough. I figured perhaps one of the solenoids was melting a coil sleeve, but upon inspection they were all fine. I removed the right popper and the trough to get a better look (I still needed to disassemble and clean the trough anyway).

Once I did this I powered up the game with high voltage on and almost immediately it became apparent that the failure was a smoking capacitor C6 on the opto 16 board. I removed the capacitor and found some damage to the traces underneath and the 1N4004 diode at D19 was also suspect. From what I'm reading it seems like C6 is prone to failure and this particular opto board is a common source of failure for this game. I did not have the right capacitor on hand so I ordered one, but I also ordered a modern replacement for the opto 16 board so I don't end up going down a rabbit hole. I'm still going to repair the other board as a backup.