Help! Big Guns C-side and lamp matrix issues!

I've been working on a Big Guns I recently bought to bring it back to life. I purchased it from an arcade owner who had had it in the place for years, and while it was kept mostly functional, it definitely needed some TLC. Since bringing it home I've stripped and cleaned the top of the playfield, rebuilt the top two flippers, installed a new PinScore LED display, and corrected some incorrect fuses. I also installed all new flasher bulbs in all flashers. The game has been suffering from an adjustment error upon booting (Factory settings when the coin door is open), but there doesn't appear to be any corrosion on the board or battery holder. The game will also sometimes buzz upon startup, and once after putting the playfield back in and reconnecting everything, a few solenoids fired when I powered on the game, and then in the solenoid test all solenoids past 16 weren't doing anything (Not even a click from the solenoid relay). After power cycling this issue went away and I haven't encountered it again since (Although I haven't done much testing since).

I'm going to try a few things to see if I can fix the adjust failure before asking for help for that here, but I'm mentioning all that stuff here in case it is useful info for another issue I'm having, which is that most of the flashers on the game aren't functioning. Only the two flashers at the very top of the backbox (Both of which are solenoid 16) and the invincible flasher (Solenoid 15) work. All the others don't seem to be functioning. All other solenoids work though, it's just the flashers I'm having issues with. Where should I go from here?

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Edit: See post #8 for info on the lamp matrix issue: https://pinside.com/pinball/forum/topic/most-flashers-not-working-on-big-guns#post-6057198

I've done a bit more diagnosing based on the above suggestions. The A/C relay is clicking when it's supposed to, fuses 2, 4, 7 and 8 are good (Which I believe are the relevant fuses but please correct me if I'm wrong), and nothing on the auxiliary board stands out as being damaged. I also tried unplugging and replugging all the connectors on the board just in case, but that didn't make any difference. I've attached some pictures of both sides of the board.

At this point I'm guessing I'll have to make some tests with my dmm, but not sure where/how. The PinWiki doesn't really offer any advice on that regard.

On another note, I resolved the adjust error issue. There was a little bit of corrosion on one of the battery holder contacts, which I cleaned up with a fiberglass pen. Seems to be saving now!

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I'm not sure I'm measuring the voltage correctly. I unplugged 5J11 and put the red lead on 5J11-4 and the black lead on ground. DMM is set to VDC 200. When I turn the game on the DMM reads 0 except for when a solenoid fires, and it jumps to different values depending on the solenoid. When I turn the machine off it jumps to about 24 and then slowly drops to 0. Same behavior for 5J11-5.

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Alright, so I haven't done any more diagnostics on the C-side issue yet, but I've discovered another issue after installing LEDs. All lights in lamp column 6 will light the adjacent light in column 7. Lights in lamp column 7 can light on their own, but their behavior is erratic (In the single lamp test they don't have a steady pulse like the others). I already checked the diodes on the lights that I thought could be causing the issue (All in columns 6 and 7), but they're all good (Had to replace a couple but that didn't fix this situation, just fixed a couple of lights that were previously not lighting at all).

I don't know for sure if this issue was present when I first got the game, but I think it's safe to assume it was because all the bulbs on column 7 were burnt out. I'm guessing this is the reason they were all burnt.

At this point I'm guessing the issue is on the board somewhere. Which I'm dreading because I don't think I have the skill or the proper equipment to do board repair. I replaced some diodes on a couple of lamp boards tonight and while I did good enough to get them working again I also did some damage to them. What should I do to diagnose the issue?

Okay so I'm planning on doing some proper diagnosing tomorrow, however I was playing the game just now and all the flashers started working during the attract mode! I immediately went into the coil test but they stopped working again. Could that be a sign of a flaky A/C relay?

Edit: Well now they do seem to be working properly. I guess I'll see if they still work tomorrow after letting the game cool down, but if this issue somehow fixed itself I'm not going to complain, haha.

Well crap... I was trying to measure voltage from the A/C relay (The C-Side coils did stop working when the game cooled down) and now all the controlled lamps are locked on. :wall :I have no idea what I could have done that would have caused this. All I did was unplug 5J11 and test a few different pins. I had the black lead on my DMM connected to the ground braid (I know you mentioned I could use 5J10, but I wasn't sure if unplugging the board's ground was a good idea, and I don't know if there's a way to clip onto it without unplugging it) near the left speaker. I had the speaker panel lying face down on the playfield glass and I tilted it up at one point so I could see the display, but there's no way I managed to touch any components with the speaker.

At the very least, I did manage to find that pins 5J11-1 and 5J11-2 are not receiving voltage when the A/C relay is activated. Is it safe to assume the relay needs replaced at this point?

I'll also go ahead and disconnect the LED OCD board and see if the light matrix issue persists.

So unplugging the LED OCD board brought the lights back to normal, but the lights in column 7 wouldn't light at all. This was not the behavior I had before initially installing the LED OCD board, it's different now.

I plugged the LED OCD board back in and the lights are locked on again, including the ones in column 7. Did my LED OCD board go bad or am I missing something?

Thanks! Btw I meant to edit my previous post with this extra info last night, but accidentally added it to another post in a different thread:

Tested Q54 with a DMM and I *think* it tested bad. There were a couple of tests that read significantly higher than on the other transistors. Should I go ahead and replace it?

Replaced Q54 and that fixed the light matrix issue! I'll replace the A/C relay tomorrow and hopefully that will take care of the flashers. Thank you so much for the help!

Got the new relay installed and the flashers are working now too! The game is now up and running 100%! Thanks again for the help!