OK....here is what happened. Wife adds credits to Gorgar and went to play. The flippers locked on and a burnt smell filled the room. Then she called out to me to see what was going on and the pin is still on.
So power was on for what I feel was a long time. This is what I can tell so far. Game boots up, light work as they should. No coil is fried and seem to work.

When a game start, the sound is messed up. Hitting the diagnostics switch on the sound boards, all sounds sound good along with voice.
For the life of me, I can not find anything burned. I will know more tomorrow as I swap boards out. I got a working MPU and driver board to test with. Oh and power supply if needed.

Other then swapping out boards, what is the best approach to narrow down this problem?

Thats a great suggestion. I did find the source of the burnt smell. Looks like Q14 (knocker) burned up. that coil is not burned up and the plunger moves freely in the coil sleeve.

The power on the power supply looks good.
38v for the flipper/solenoid
17.4v for the lamps
do not use the HV section
10.4v in the 5v section

Sound is still messed up. The heart beat is missing at start up. 3 high tone beeps is all that I hear.

I was measuring at the fuse holder F5 to get 10.4v. So I measured at 3J6 this time and found that I have 4.78v. I tested on the 5V test point on the CPU and it had 4.75v.

I found Q14 burned up. I have not replaced it yet. For the time being, I cut the wire going to the Knocker.

I "good"back up board, will not get out of the Audit mode. So I am stuck trying to test the original MPU and Driver board. So for now the Pin boots up and plays, all coils but the knocker are working and I have sounds, just not the right sounds in some parts of the game. Also no heart beat that plays continually in the back ground.

As far as the flippers locking on at boot up, I'm guessing that there must have been a power surge at some point causing the flippers to kick on. And maybe some of the other coils kicked on too. Don't know... just a guess.

But I'm stuck on the why I lost certain sounds and how to get them back.

Changing out the CPU and PIA did not make a difference.

Changing out the driver board fixed the issue. Now I need to figure out what is wrong with the driver board.

I just found it, IC4 got burned up. I didn't see it until I got the magnifier got. Replace it and it is working now. Something really shorted out. I don't think that I'm going to repair the knocker. It had a very low dud sound and besides Gorgar tells you when you win.

Still have one more problem. Lamp column drive #5 is not working. Checked Q70 and Q71 and it did not test bad. Makes me wonder if IC14 is bad.

Lamp column drive #5 still not working after checking Q54 and Q55. Even swapped IC17 and IC18 with no change.

Ok, Out of frustration, I install the other Driver Board. It had the same problem with Column #5. Either I got the same problem with both Driver Boards or I got a playfield problem.

Well, I thought that I would close this thread with what I found. I found that all the bulbs in column #5 had blown or melted.

20210723_102019 (resized).jpg

I would like to know that myself!

6.3v

No history on the machine. it was dead when I got it over a month ago. No power surge, change of wall socket or generator. Been playing great since I got it working....till the other night when something shorted out.

I had to rebuild a small section of the board due to battery damage. Replaced all connectors and headers along with the 40 pin connector. Also had to replace IC2 on the MPU board because of a difference solenoid problem.