In my haste of adjusting my sanctum switches I screwed up. I had the coin door shut and accidentally touched a switch blade to a coil and blew out column 6 on my MPU. The game basically shut off and then powered up again immediately on it's own. In addition to column 6 being out, three optos stopped working. I don't know if the opto issue is related to the short but they were working prior. I believe my issues is the 10 switch opto board under the playfield. Can you review my diagnosis and let me know if my logic is flawed prior ordering a new one?

1. Swapped MPU boards with a working board and column 6 now works fine. All switches work except the three optos oultlined on the switch matrix in red (31,32,33).
2. For good measure I disconnected the switch column and row connectors at the MPU and ran jumpers to test the board. The switches (31,32,33) register fine. I think it is safe to say the MPU is not the issue so I moved down the line.
3. I tested each opto in question on the playfield with my camera. The LED/emitter is on. Because I can't test the receiving side with a camera I replaced the receiver on switch 33 with no luck. I think it is safe to say the optos themselves are fine. This leaves the board.
4. Checked all connectors on the opto board for broken solder joints, etc. All looks good.
5. One fuse controls the switch matrix so that isn't the issue.

All other optos running from the 10 opto switch board work fine. You will notice on the board diagram outlined in red that those three switches have independent connectors running from the board to the optos. I don't think those are an issue as the playfield optos are working fine when testing with a camera. I believe the issue is somewhere on the board or between the board and the MPU as the MPU is not detecting activity for those three optos. I just find it strange that the short could only impact those three switches (other than blowing up column 6). Why those three? All other switches in the matrix work. I think my issue is somewhere highlighted in red on the schematic. A new board is around $80, I just want to make sure my logic isn't flawed before ordering. Am I missing anything? I hope I described this clearly.
Opto Board (resized).jpgOpto Board Schematic (resized).jpgSwitch Matrix (resized).jpg
Opto board parts (resized).jpg
20200213_071458 (resized).jpg

Thank you kind sir. I might have a go at soldering. I have done board work before although these are quite small. Strange how those three went out from the short. Wish I knew why for my education but maybe current travels in strange ways? I will definitely report back. I order a new board as well. Doesn't hurt to have a spare or I can resell if I fix before it arrives.

Any difference between LM339 and LM339N?

All these problems surfaced because when you locked a ball it would kick out randomly when playing. Particularly when actuating the flippers. In switch test I noticed a couple of those switches in the sanctum would flutter. I'm talking very random quick flutters that you wouldn't catch in switch test mode unless you were really looking. I didn't know what was causing it. Figured the balls weren't resting on the switch stack very well as the switches never fluttered unless balls were locked. I assumed those slight flutters confused the game and it was kicking out balls due to it. At least I am hoping that was causing it. I adjusted them a few times and the last time i cooked the board. I never work with the door closed, go figure. They didn't flutter with the i500 mpu in place so I am hoping that issue (original issue) is resolved either with a new U13 chip or I tweaked the switch blades sufficiently. I always hated those switches up there. Very finicky.

Just a follow up. New opto board fixed it.