I am trying to restore a Bally Motordome that I bought from a wire hacker. During the previous owners "troubleshooting" about a dozen playfield wires were cut and hanging. Using the schematic, each switch and light was carefully checked back to the MPU. I found about a dozen power transistors and scr's bad. All were replaced.
All switches and lights word perfectly, that is for about 25 minutes. I consistently have the following lights fail and once the scr's are replaced, it plays again for about 25 minutes:
Q37 (B LAMP) RIGHT THUMPER LIGHT
Q37 (A LAMP) TOP "R" LAMP
Q69 (A LAMP) TOP "M" LAMP
Q41 (A LAMP) TOP "LEVEL II" LAMP
All diodes on the lamps were checked and although tested good, replaced with 1n4004 diodes, and rechecked good.
The scr's originally were 2n5060 and have been replaced with 2n5064.
The game came with a spare 6803 MPU, I made similar repairs to this MPU and have the same issue. After playing for a short time, I loose the same four lights and the scr's are bad. Once replaced all lights work again, for awhile.
All voltages on the Power supply board test good, the MPU voltages test good as well.

I re-flowed all the pins on both MPU's.

I am stumped what to do next. Any advice would be greatly appreciated.

Thank you,
Mike

The 2n5064 was suggested by Great Planes. I have used about a dozen of these on the two boards that Motordome came with. The only place I have trouble is the three listed. I failed to note, I also checked the cap's on the switches, all tested good at about .01uf,

After I install a "repaired" MPU (new 5064's) the lamp test is good. The game starts and plays. It is hard to tell when I loose the lights because during game play, these lights cycle on and off normally. I always pick it up during initial powerup, all the lights come on and flash. I always catch the big red right hand thumper not on - always an oh no moment.

I checked all the 2K resistors all look fresh and tested good.

Two of the scr's are tied to one of the 4514's. I ordered (6) replacements at this point I will replace the first one on one of the boards to see if that helps. I was also thinking about soldering in two transistor sockets on one of the MPU's. It would make changing the scr's a lot easier while I troubleshoot.

Used long ago in old electronic equipment, still found on ebay.

It uses the wedge style bulbs, 555 I believe. I changed all the bulbs when they didn't work. The bulbs I removed tested ok, but I changed them anyway. I expect the 4514's later this week, I will change them just to eliminate them as suspects.

I ordered a handful of the old transistor sockets and I am going to carefully solder them to the cut off legs of the scr's. I am tired of pulling the MPU and replacing the scr's. I have done both boards multiple times. I know it's not good for the molex connectors, or the board traces. After I plug in a new scr, I am going to try to repeatly trip switches that effect each feature and see if I can make the scr fail.

The problem with trying to figure out when the failure occurs is during game play the lights naturally go on and off. You have no idea when the lights shutting off is game initiated or the failure.

Sorry about the slow response I was unexpectedly out of town. I will check the fuses this weekend. In the mean time, I have cut the last failed scr's off the second MPU and have soldered on three sockets to make the scr's plugins while I continue to troubleshoot. I know continually pulling the MPU's is hard on the molex connectors and the continual solder and desolder is not good for the traces.

I figured I would install the other MPU and pick a target cycle it 20-30 times and see if I could get one of the scr's to fail. Maybe this would give me an area to look at more closely. I am truely lost on this one.

Changing the 4514's was due to running out of things to check, it is the next component in the system.