To the thread, I have found that I am stumped. Long post, but trying to channel my inner Engineer by providing all details that I can think of.
Original Williams Medieval Madness game that I am shopping. Game was working fine before I started playfield shop, took the pf down to the wood, placed a Makrolon protector on it and reassembled the pf.
When I got the game, the left troll was not working, but assemblies were replaced by the Planetary Pinball brackets, so both Trolls were functioning. I also replaced both flipper assemblies with new brackets/kits. The game has been routed since its purchase in 1997, so i felt justified in replacing Troll brackets and flippers.
After top shopping was done, game was working fine again. I could play games to completion without any issue.
One day I saw that the left flipper was not working during a game. Stopped game immediately and saw that the flipper coil had locked on. Flipper coil was burnt, so no more playing before I diagnosed this. I see no burnt connectors but fuse F116 (+50 volts 4.0 A, left flipper) was blown as well.
My diagnostics told me that the suspect transistors Q89, TIP102 and Q87 TIP36C could be blown for the coil to lock on. Replaced, Q89, Q87 and F116. Left Flipper coil is also replaced of course. No binding in flipper after replacing coil, it moves freely. Left EOS switch checked in Switch Test and works fine.
Now I have the following: game plays, as I turn on the game, start button works to start a game and game plays normally (as far as I can tell). Right flipper does its job and flips. Pushing the left flipper button causes the game to reset. Game shuts down and reboots.
Left flipper button when pressed not in a game does nothing. It is only when the flippers are energized during a game does the left flipper take it out.
I have read (but not exercised) the list of WPC Resets as suggested many times on this site: https://www.pinwiki.com/wiki/index.php?title=Williams_WPC#Game_resets
I am guessing that the left flipper during game play is shorting the 5 Volt to the MPU, but as the Fliptronics circuit is on the WPC-95 Power Board, I am at a loss to figure out what is going on. Left flipper wired directly to the power board if I have that correctly.
Any hints, threats, or "you dummy, this..." are appreciated to help me isolate this problem. Guide me towards some place else to follow other steps if that works for you.