Little backstory first - I have the Rottendog MPU board just in case that matters. My #BSD was running almost perfectly when I decided to add a spotlight to the graveyard area. I tested it out after installation, and it worked fine, and game didn't throw errors. I've been having an issue with the middle pop bumper being weak, so I checked that out after powering down the game (but I left it plugged in). As I was adjusting the switch, I felt a little shock but didn't think twice about it. Powered the game back up, and I was greeted with the F114 and F115 message. F114 continuity was good after taking it out, and F115 was visibly blown, and had no continuity.

Now onto the stupid part. I didn't have a 3/4A fuse, so I threw in a 3A fuse to F115 just to see if it would work after. F114 and F115 message went away, and I was getting some weird ground loop issues and check switch matrix errors for the middle pop bumper and drop targets, and I think a bit more, but I powered off the machine before I could take a picture.

I've since received 3/4A fuses, and when installing it to F115 it blows immediately. So, I've been going through the pinwiki troubleshooting steps, and have been doing well until checking for 12V at pin 2 of J114.

I had no fuse in F115 at first because I didn't want to continue blowing while testing. When I powered on the game with the J114 connector undone, I blew the main 8A power fuse for the machine. So after replacing that, and installing the correct 3/4A fuse in J115, I'm blowing the 3A fuses at F104 and F105 before I can even check for 12V at pin2 J114.

I'm hoping for some insight before I keep blowing through fuses trying to figure this out.

Yep, the F104 and F105 go to the coils. I'll check all of those when I get home. My F114 didn't blow, even though the message that pops up says "check F114 and F115." F115 blows when I start the game, and that goes to the switch matrix. I don't have any experience troubleshooting that, so I need to do some more research.

I just wonder if that my symptom of the F104 and 105 fuses blowing when I disconnect J114 is the same thing that's causing the F115 to blow.

Disconnected J210 on the MPU, and F114 and F115 did not blow, but F104 and F105 blew immediately. Which from what I gather it means that I have a short somewhere in the playfield.

I tried to research how to check U20, but I don't know what you mean by pins 9 and 10. Are those the two that are farthest to the left on the U20 chip? If so, I get a reading of 0 when I set my DMM to 20M ohms. If it is bad, thankfully it's socketed on the rottendog board.

In the meantime, I'll start looking under the playfield.

So I put new fuses in F104 and F105, and disconnected J127 and J130 and started the game - with J210 connected on the MPU, and no fuses blew, but I took a video of the errors that it detected (which I'm guessing are because I disconnected J127 and J130). It read:

Check switch 51 opto TR Lane, 53 opto castle 1, 54 opto castle 2, 55 opto BL popper, 56 opto TL popper.
Also, check magnet left, right, and unload errors, and top right ramp up errors.

I'm getting more confused as to what I'm even looking for.

I've got 10 U20s that'll be here on Saturday. It'd be crazy if all my issues are stemming from a bad chip, but I hope that's the case.

I put good fuses in F104 and F105, and tried with only J127 plugged in, and then with only J130 plugged in, and neither blew a fuse. Figured I'd try with everything plugged in again, with good fuses in F115, 104 and 105, and no fuses blew, and it showed the same exact errors I listed earlier.

It seems that F104 and F105 only blow when J210 is disconnected, and when J114 is disconnected.

Maybe this is all a symptom of my U20 that's bad?

I think you're right about this. But it still makes me wonder why they blew when I was checking pin 2 of J114 when going through the pinwiki troubleshooting steps here https://pinwiki.com/wiki/index.php?title=Williams_WPC#Check_fuses_F114_and_F115_message

The errors I'm getting now are entirely different than what I was getting at the beginning.

Pulled out U20, and no fuses blew. The error message read "Check Fuse F114 and F115" again. I'll plug in a U20 when I get them in the mail tomorrow.

With a brand new U20 plugged in, I'm getting these errors:

Check switch 51: Opto T.R. Lane
Check switch 53: Opto Castle 1
Check switch 54: Opto Castle 2
Check Switch 57: Opto Castle 3
Check Switch 84: L. Ramp Score
Magnet right, left, and unload error
Top right ramp up error

Any advice for my next troubleshooting tests? I've never had a switch matrix issue before, so I'm researching how to test this. I'm a fish out of water here.

Thanks everyone for the help so far!

Did as you requested, and everything registers when I test. Tested everything just in case, and double checked to make sure that the specific ones that were giving me errors were in fact working. So I think that rules out the MPU. I don't have any alligator clips, so it required a steady hand

I'm guessing that J206 and J207 are interchangeable. My cord was plugged into J206, but the switch matrix in the manual lists J207.

Thanks! I can actually understand what I'm doing when testing the switch matrix now, so that's a plus. It looks like all of my errors are opto related now. Going to look in the manual and see how I can test it.

So I just plugged J206 and J209 back in, and for some reason I'm not getting the opto errors anymore. Only the right left and unload magnet errors. Just to verify that the optos are in fact working, I tested all of them, and they're good. I'm going to lift the playfield and see if I have a loose connector somewhere.

Nothing is working with the magnet right now, and that seems to be the only issue. EDIT. Powered off again and powered back on. It's not giving me magnet errors anymore, but the motor that moves the magnet isn't working. The magnet itself appears to be loading and unloading correctly. Just isn't moving.

Did some more searching about the mist motor issue, and found that fuse F111 a 5A was blown. Replaced it with a 3A to test since I don't have a 5, and the motor is working.

I have no idea how all of these problems seem to have resolved. U20 was definitely an issue, but my problems persisted even after replacing it. It took a handful of power cycles, and unplugging/plugging in the machine to get it working. I'm going to play a handful of games with it to see if anything shows up, but for now, it seems to be working.

Your thread was the reason I even checked F111, so I was pretty happy to stumble upon it. I'm still thinking that I've got a short somewhere in the playfield that was causing problems, so I'll troubleshoot that when I next start having problems. Otherwise I'm leaving everything closed up so I don't ruin anything.