Quoted from gdonovan:

Well my day just went to hell in a basket.
Edit: Disregard post, unless you want some entertainment. I have no idea what happened, I really don't.
Going through no led troubleshooting I noted that TP2 had no voltage (expected 12V) found broken wire at stupid IDC connector.
Repaired wire and everything works perfect now, I'm at a loss but happier.
Display works fine as well.
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So I'm starting to reassemble my Flash Gordon after doing a cabinet refurbishment. I very carefully plugged everything back in making sure no connectors were swapped, grounds hooked up, etc. And then checked them again. And for good measure disconnected the two connectors at the solenoid board J2 and J5.
So I powered up the machine...
1) The MPU led locked on and stayed on. On the credit display there was a "0"
Shutting the machine down I checked all connections again and powered back up again. Pulled all connections off lamp driver board except J4 and unplugged the switch lines on MPU
Now the MPU is stone dead.
Decided to check for 5 volts at TP5 on the MPU, HOLY COW 50 VOLTS.
Shut machine back off, unplugged the J4 connector on the lamp driver board and the connector on the sound board.
Now I have 5 volts on TP5.
If I plug the J4 back on the lamp driver board and power up I have 50 volts again on MPU TP5.
I unplug the connectors on the power board in the lower cabinet and examine them one at a time, I see nothing amiss. I check ALL the connectors again, everything is plugged in where it should be.
I power up and check TP5 again, 5VDC. I plug the J4 connector back in the lamp driver board, now it shows 5VDC.
What the hell happened? I swear the meter was showing 50 volts DC on TP5.
Ground is good, TP3 is showing 21 volts as it should and TP5 now showing 5V.
The only other thing I see that is odd, one of the displays is not glowing and the other four are. All of them were working perfect before taking the machine apart. I have it unplugged for now just to be on the safe side. Moving displays the problem follows the single display. I looked close at the display connector and pins and all looks fine.
Edited: Sound board passes LED test and when you hit self test button it goes through its paces. Whew!