Newb at posting and fixing here. I have a Simpsons with what I think are two separate problems, or maybe not. The down and dirty is that I keep blowing the F-5 fuse and the Transistor at Q5 the TIP36C, on the Playfield Power Board, (PPB). I have been trying to troubleshoot this since Jan. of this year to no avail. Problems started with the power up and the Laser Kick coil fried, bad. Replaced Coil, its diode, the Q-5 transistor and the F5 fuse. Power up, blow Q-5 transistor and F-5 fuse. Have tech come to house, he replaces the aforementioned parts and it works till I power up two times later, back to the same thing, take machine to shop, advised everything in circuit replaced, playing fine in shop, bring it home played maybe 5 more times, back to blowing transistor and fuse. Trying to figure this out, and fix it once and for all.
When the game is turned on, with the parts blown, and before starting a game, hitting either flipper with make the laser kick shoot out, and the flippers move slightly. When the game is started and when either flipper is hit, the laser kick shoots out and you can hear the coil humming, and it is immediately shut down.
Please, give me a starting point to diagnose this machine. I have tried reading past posts, but no posts seem to hit on this exact problem.
I have checked grounds from the plug to the boards and between, including all screws in all boards, there are no breaks in ground that I can determine. I have replaced the Tip36C transistor and the F-5 fuse with the proper replacements, so i really dont want to power this up until I have checked everything possible beforehand. And that’s where this community comes in, any help is greatly appreciated!
Gary

Frunch, ran into a small Covid problem, but as soon as this clears I will change out those components and post back. Thanks for the response.

Frunch, The resistor array at RA25 checked within tolerance. And both the TIP122 and the 2n4401 were replaced, by the tech at the shop. However, the 2N4401 was replaced with a 2N3904-H25 could this be a problem or is this just a stronger transistor for that slot?

Yes, the diode on the laser kick coil was changed when the other work was done, but not since I changed it this time but, a check of the diode with one leg removed show it to be working. So I’ve ordered the 2n4401 and will replace it, and the Tip122. With that done, do you think a power up, would be safe to try?

So the 7406 chip was replaced the tip122, 2n4401. And as previously stated the tip36c and f5 fuse were replaced. Within 4-5 seconds of powering it on, it blew the tip36c and the coil for the laser kick shot out and remained out until powered down, within 1-2 seconds. Talk about frustrated!!!
Edit: any bad caps on the power supply board we’re replaced back when machine was in shop last Jan. I believe!