I'm not sure that I can make a short post on this question, so forgive me in advance if I post too much information.

I picked up this machine with the description of: works sometimes. I turned it on to find that everything works except most of the coils (the knocker and lockout work). After it being on for a bit, everything started working. This didn't last long (a couple of games). I don't remember the order, but here is what I've done so far:
Checked the test points on the solenoid driver board. All checked out fine.
Checked the test points on the rectifier board. All checked out fine.
Used a test lead to trip each coil by touching each TIP102. Only Q3, Q15, and Q19 work when the game isn't started. Only Q3 works with a ball in play.
Tested each TIP102 with a DMM. All tested fine.
Put in a known working solenoid driver board. (Same issue, but everything started working for a short time, but quit after a few games).
I retested the solenoid driver board to make sure that nothing got fried. All tested fine.
Checked continuity from the coils to J5 on the solenoid driver board. All check out fine.
Replaced the connectors on the solenoid driver board.
Replaced the header pins on the solenoid driver board.
Completed the ground mods on the solenoid driver board.
Replaced the connectors on the rectifier board.
Replaced the header pins on the rectifier board.
Replaced F5 fuse clips (they were a little discolored) on the rectifier board.
Re-flowed both the solenoid driver and the rectifier boards.

I may be missing something that I did, but I think that I including everything.
Most of the above takes place to all older Ballys that come in anyway.
I have not replaced the connectors on the MPU. That would be next, but I thought that I'd go ahead and ask for help as I take a break.
I haven't been able to get everything working, even for a short period, lately.

Thanks in advance for any help offered up.
Miles

Thanks, I did. I also replaced that fuse holder as well.

The game worked for about 30 mins, and then the coils mentioned above stopped working again.

Any other ideas?

Just to give a little more information, it has never worked correctly on start up. While it was working correctly, I have turned it off and on with success, but it has never worked correctly the first time that I turn it on. I have checked the test points when it was working, and when it wasn't. I get the same results. The flippers are included in the issue...they work when the other coils work, and they don't work when the others stop working. I have an Alltek SDB in my Eight Ball. I put it in the Skate Ball, but I'm not super familiar with its diagnostic abilities. I know that it will tell me which solenoids aren't working, but I know that from testing them. I am planning to pull the Skate Ball components and try them in another machine this evening to try to isolate the problem. I was hoping not to have to move the playfield, but I will if needed. Thanks for the advice.

As I was getting ready to start pulling boards to test in other machines, I decided to give the playfield and wiring harness another look. I found that a diode on a switch at the top of the playfield had one leg disconnected. I didn't take time to look at the schematic to see if this could be the culprit, but I did solder it back on. After I finished my inspection, bingo! I turned the machine on, and everything worked. With the hit and miss nature of the machine, I was skeptical, but after leaving it on, cutting it off and back on, and then checking it again this morning, everything seems to be working well. I went ahead and upgraded the bridge rectifiers.

Thanks for the suggestions.