Medieval Madness: Pinball Repair Log

My wife and I are now the proud owner of one of the grail games of pinball collectors: Medieval Madness. We bought it from a game room store on September 3rd, and it ended up having some issues when we got it home. I have been gaining a lot of confidence repairing this machine as all of the issues have been pinpointed withing a couple of hours. So, I am enjoying my time repairing this machine. On the plus side, the machines warranty includes all the parts I need for 90 days.


  1. Left Flipper Malfunctions:
    • Flipper stays up for about a second after release.
    • In Switch Edge test mode there is a hum/buzz that occurs as the lights on the switch matrix display are finally turning off. (This sound emanates from playfield, not the speakers.)
    • Lane Change: At one point I saw the “R” and “E” alternate back and forth after the left flipper button is released. (I assume all four of the letters to spell “FIRE” do this, but I haven’t watched closely enough to verify.)
  2. End of Ball / Multiball.
  3. Flash Lamp Shorts.
  4. Catapult Kicker Power.
  5. Right Troll Inconsistency.
  6. Castle Gate Inconsistency

Left Flipper

  • [9/5] The flippers on the WPC machines use optical switches instead of leaf switches. There is a “F” shaped piece of plastic which normally blocks the opto switch light. This plastic was leaning slightly away from the opto board, which was apparently causing these crazy things to happen. I also discovered the left opto was missing a piece of spring steel. Transferring the steel piece from the right flipper resolved the problem.
  • [9/14] Installed new piece of spring steel on the left flipper button assembly, and returned the other piece back to the right side to resolve the problems.

End of Ball / Multiball Issues

  • [9/5] A new acquaintance of mine told me the balls are getting caught high in the trough so the opto switches are not registering the balls presence. The solution is to replace the old dented ball trough. Until the trough arrives, we just have to give the game a jiggle to free the balls.
  • [9/14] Installed a brand new replacement trough engineered by Mantis Amusements. This trough adds a steeper incline, and uses inexpensive replaceable rods. And, the next time our trough has problems, flipping the rods over gives the trough new life! 🙂

Flash Lamps

  • [9/5] Playing Pat Choy‘s MM made me realize our the flash lamps were not working.
  • [9/9] Discovered a blown fuse.
  • [9/10] Luckily every flash lamp had quick disconnects, so troubleshooting involved unplugging every flash lamp under the playfield (I now realize there are 4 flash lamps behind the translite as well). Then installed a new fuse, and began plugging one lamp in at a time until the fuse blew. The problem was a #89 flash bulb which lights up the green moat plastic. The base had broken loose and was causing a sort. Repositioning the base resolved the short (at least temporarily).
  • [9/12] Discovered the lamps lighting up the green moat trough are NOT supposed to be lit constantly! Uh oh! I disconnected the moat lamps (via the quick disconnect) to avoid the lamps melting the moat plastic any more than they may have already done.
  • [9/13] After reading Clay’s Williams WPC repair documentation (at /, I believe the transistor(s) that turn those lamps on have developed a short.
  • [9/13] Both the TIP102 and its predriver transistor have been requested from the seller. Hopefully replacing these transistors will resolve the problem, and we won’t end up having to replace anything further up the line (like the chip that tells those transistors when to activate the lamps).

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