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).

Comet: Pinball Repair Log

Comet is one of two non functional pinball machines I picked up for at a Garage Sale about two months ago. The other is Space Station (whose repair log is here).


  1. Battery corrosion — but no leaks.
  2. All displays are dead.
  3. Display Power Supply voltage problem.
  4. All ramps are damaged to some degree. The middle ramp needs repair.

Batter corrosion.
[7/13] Removed corroded battery holder and replaced it with an off-board battery holder. Game powered up and played very well (except of course for the lack of displays, and middle ramp issue). Luckily the corrosion does not appear to have spread.

All displays are dead.

  • [7/13] The glass looks scorched. Will have to see if any of the displays work after I repair the voltage problem. I suspect I will end up having to purchase a new set of LED displays.

Display Power Supply voltage problem.

  • [7/17] 100 volts was missing on one of the two 100v pins. When I was feeling around for overheated components, I touched the heat sink of one of the transistors and got a little zap! Since the heat sinks of a transistor should be ground, I believe someone hooked up a replacement transistor without making sure the correct leg went in the correct hole (often replacement transistors legs are in a different order than the original component).

Ramp Damage: Middle / Roller Coaster Ramp

  • [7/15] Side walls at entrance appear to have melted slightly and lean far to the right. This prevents the entry gate/switch from moving out of the way of the ball. With gate removed, a large bump at the entrance still makes entry almost impossible and causes many airballs to fly hard into the glass.
  • [7/16] After talking it over with several people, and doing some reading, we will probably use a heat source to soften the ramp enough to allow us to reposition the warped walls… and perhaps lower the bump. Per the suggestion of both Shane and my father-in-law, we may attempt to use some kid of resin to reattach the cracked lip at the very front of the ramp.

Space Station: Pinball Repair Log

Space Station is one of two non functional pinball machines I picked up for at a Garage Sale about two months ago (the other is Comet). I decided to start with this one because it is at least partially playable. 🙂

Here is a list of issues I have discovered.

  1. Player 3 Display is out.
    • Display Power Supply voltage problem (+/- 100v = 120v/-130v).
  2. Left Dock Kicker (does not kick).
  3. Top Pop Bumper (does not bump).
  4. 2 balls get kicked into the launch bay (at the same time).
  5. Right Flipper is sloppy.
  6. Right Dock gate installed backwards (not allowing the ball to escape).
  7. Stuck switches (x 5).
  8. Rubbers need replacing.
  9. Plunger power barely/not always enough to get ball to top of playfield.

Player 3 Display / Power Supply voltage problem
[6/20] I believe I will need to rebuild the +/-100v section of the display power board. If the missing display functionality is not restored, with the correct voltage applied I will have to buy a new display (e.g. Pinball Life).

Left Dock Kicker
[6/22] Coil gets 80v of power; does not fire in “coil test” mode nor “in game”; further coil would not fire when shorting to ground. I removed the coil, and it has continuity to both solder points, and it tests at about 4.2 ohms of resistance. I don’t know if the coil is bad or not, but I suspect it is bad.

Top Pop Bumper

  • Misc. bulbs out.