If you disconnect 1J-12 from the cpu board then turn on the game power the AC relay will stay on the A side so that you can check the brown power wire on the 2a coil. I would look for a almost broken brown wire on this coil or the coil connected prior to this. I would give the brown wire a tug to see if it pops off, if not follow to the prior coil and pull on the wire. Now this is if only the one 2a coil is not working. If all the coils on the A side are not working then you need to look for a cracked header pin on the innerconnect board.

Sounds like you have proved that the brown power wire is good.

Removing 1J-12 will keep the the AC relay from energizing, thus keeping power on the brown power wire for testing purposes.
Then check for voltage on the violet/red wire at the coil, 5J4 pin8, 5J1 pin7 and 1J11 pin3. Now checking for voltage without a load on the circuit sometimes doesn't find the problem. If the wire is hanging on by one strand it will show good voltage but will not pass enough current to operate a coil. This why some techs use a jumper to ground to test instead of a volt meter.

Yep. Since you never said that 02c spinner flashers didn't work, I assumed that the CPU was working fine. You can touch the ground jumper to the metal tab of Q-25 to see if it is a cracked header solder joint. If the coil fires then I would test Q-25 to see if it has gone bad.

Most likely, but it can also be Q-21. I usually replace these in a set. Q-25, Q-21 and D-2 on the aux power supply.

Here is a short video on testing with a DMM.

I only buy 1n4007 diodes are they are more robust and can be use for any 1n400x diode. Also use TIP102 for TIP122 as they are 60 % stronger.

Playball!!