- misc pinball fixings and non commercial pinball help

Attack from Mars: Game resets when freeplay knocker fires

Issue: Game resets when freeplay knocker fires. This does not happen always, but most of the time.

Solution: First, voltages for +5v and +12v where checked, and they are both rocksolid, even at reset time. Power Driver was swapped with a known good board, issue remained. CPU was swapped with a known good board, issue disappeared - so we know the issue is on the CPU board or with some intermittent connection. Swapped original board back, issue returned.

It seems the problem is vibration based - the knocker causes the components to vibrate a bit. Using a small piece of plastic, i started knocking slightly on components - it turns out that by slightly knocking U4 (the 6821 CPU) the reset would occur.

Taking the board to the workbench and removing U4 reveals corrosion that seems to be a remainder of an improperly cleaned battery leakage.

I desoldered the socket, and you can clearly see the corrosion on pins 4,5,6,7. The other pins dont look to good either


Other side of the same socket, no corrosion visible


Soldered in a new socket for U4, cleaned the pins of the 6821 and reinstalled in machine. Issue no longer appears. Another one done!

Mousin Around: Display segments and digits missing

Issue: The right display is missing two segments on each digit, plus the last digit is missing totally.


As you can see, the last digit is missing (a zero) + the left two segments are missing.

Solution: Lets start with the missing segments - System 11 displays are controlled by strobes (which are all the 16 digits) and segments (eg the -- in a digit). The display tube is being strobed constantly so your eyes don't realize that the digits are not lit at the same time, but serially. For each digit being strobed, the corresponding segments are being triggered.

This problem is unusual; most typically you see segments stuck on and not stuck off. Basically segments are triggered via 4049 Hex inverter IC and an UDN7180A (these fail quite often, but usually cause the "segment stuck on" problem).


As a quick test, i swapped a know good display over from a "Game Show" and the issue remained. Therefore the display itself can be excluded as the source of the error -> we now know that the issue comes from the main CPU board or the display cable. Swapping the cables over yielded the same results - its gotta be CPU.

Using the schematics to trace back the missing segments, the culprit was most likely the 6821 PIA at U51. Using a basic DMM - red lead to ground and black lead to probe the pins - revealed two pins that had different values than the rest. So the 6821 needs to go...


When soldering in a new IC, always use quality sockets. Don't be cheap. Anyway, a new PIA is in place and voila - the missing display segments are back.


Alright, next up - the missing digit. Looking at the schematics, we are looking for last strobe, the last digit of the display. In that case the answer was quite easy - oxidation ate away one of the display connections within the glass tube.


Simple, but expensive fix - replace the display tube. These are really hard to get nowadays and expensive as hell - make sure that the tube is really to blame before doing this. Anyway - tube changed and all was well.

The ultimate rule guide to Stern's Star Trek

undefinedThe Stern Star Trek pinball machine rule sheet
(c)2018 Georg "hiho" Hinterhofer

Alright folks, seeing that its almost 5 years after it's release and we still do not have a comprehensive rule sheet for Stern's Star Trek, i guess its time to come up with one. With the release of the VE on the horizon, people will - again - be looking for one.

DISCLAIMER: This is my first attempt to write a rule sheet (don't be too hard on me), and aimed towards the novice and advanced players, not pros. It is also not aimed towards competitive play - tournament mode is not considered here.

Any additions are highly welcome - send them to Some of the facts presented here were already discussed on other platforms, and I've tried to give credit wherever applicable.

This is purely a labor of love. It is freely distributable, as long as all references as well as the authors name and contact details remain with the document.

MACHINE USED: This rule sheet was created using my HUO Star Trek Premium. Whilst the same layout as the LE, the PRO is missing some features like the left kickback, the laser star field and the tilting vengeance.

FIRMWARE: At the time of writing, the latest available software was 1.62, which was also used.

MANUAL: The current manual at the time of writing was

SHOT MAP: At time of writing, the shot map was located here -



0.1 Initial writing


Inspired by the Star Trek and Star Trek Into Darkness films, the newest Stern machine puts players in Captain James Kirk’s chair of the U.S.S. Enterprise, embarking on a journey to protect and defend the planets of the Federation. [1]

To progress towards the wizard modes and finale, the player needs to battle out differently themed missions that are all placed around the first two Star Trek reboot films.

PLAYFIELD LAYOUT starting from the bottom left going clockwise -

Left Lower Flipper: Your standard, 3" white flipper bat.

Left Outlane: Light's "T" of TREK, either goes to the outhole or kicked back when the kickback is lit.

Left Inlane: Light's "R" of TREK, feeds to the left flipper and from the left ramp and left scoop.

2 SHIELD Targets: Relight kickback - see below for more information.

Left scoop: Starts missions and locks balls. On Premium/LE this feeds to the left flipper via an up-kicker to the left ramp, on PRO this simply kicks it out, trickling back to the player.

Leftmost Black-Hole/Red Matter Target: Award hits towards black hole award.

Left Orbit/Spinner: Feeds to the top rollovers and upper right flipper for the warp ramp shot.

Green Lock Targets (3x): Those targets lite locks (left scoop and center vengeance shot) for Klingon Multiball. See Klingon Multiball for detailed Info.

Warp Ramp: A diagonal ramp you can hit from the right upper flipper. Awards Warps for Extra Ball, Score Multiplier and Add-A-Ball. Feeds to the upper right flipper.

Warp diagonal Black-Hole/Red Matter Target: Award hits towards black hole award, can be hit from upper right flipper.

Left ramp: Feeds to left flipper via the left inlane, can easily be backhanded.

Center Black-Hole/Red Matter Target: Award hits towards black hole award, to the right of the left ramp.

Vengeance Target: The center shot of the game, can be hit from both sides. When hit it can jump right up again or stay down, revealing a magnet behind it. If it stays down, there's a kicker in the back that can fire back the ball brutally at you (like Yagov kickback in F14).

Black Hole Target: Awards random award, see Black Hole awards.

Pop Bumpers: Your standard 3-set of bumpers, in class left-right-bottom arrangement. Award bumper hits for super pops and regular pop bumper levels.

Top Rollover Lanes: Called BEAM ME UP-Lanes, they advance the bonus multiplier.

Right ramp: Feeds to the right lower flipper via the right inlane.

Right ramp Black-Hole/Red Matter Target (2x): Award hits towards black hole award, to the left and right of the right ramp.
Right Orbit: Feeds to the top rollovers or comes down the left orbit.

Upper Right Flipper Finger/Galactic Away Team: Allows a ball to get back to the shooter lane by raising the upper right flipper; otherwise, your standard, 3" white flipper bat.

Weapon Targets (3x): Loads up photon torpedoes to hit Vengeance by using button on lock down bar, see Photon Torpedos.

Right lower flipper: Your standard, 3" white flipper bat.


Your main objective on Star Trek is to play through the various Missions available. Every mission is structured into 3 separate submissions, declared by roman numbers I,II and III, getting harder as you work through them. You have different ways to start a mission:

  • On ball start, you will be offered a choice of missions to start from, except when a vengeance mode is lit. Plunge the ball or hit the lockbar button to choose.
  • The scoop, when lit (blue arrow), will let you choose and start a mission. Hit the lockbar button to choose.
  • The galactic away team (blue arrow), will let you choose and start a mission. Hit the lockbar button to choose.

You cannot start multiple concurrent missions, eg no mission stacking. You can however stack a mission with multiballs. A popular strategy is to start a multiball shortly after you start a mode, therefore giving you a decent chance to finish off the mode while actually collecting Jackpots or other relevant shots.

The 6 Missions, and their associated colors, are (the big triangle in center of the playfield) -

  • Prime Directive - Dark Blue
  • Klingon Battle - Red
  • Destroy the Drill - Light Blue
  • Nero - Purple
  • Save the Enterprise - Green
  • Space Jump - Yellow

Those colors are also the colors that the Star Trek insignia will be lit to identify the shots to be made for mission advancement/completion. Finishing any three missions in a row will award The Captains Chair - see Captains Chair for more details. Finishing a mission 3 levels deep (three in a column) will lite a shot multiplier (2x) till the end of the game - see Three in a Column. Finishing a level of modes (eg part I of all modes) will lite a wizard mode - see wizard modes.

All Level 1 parts are timed, while level 2 and 3 parts are sometimes not. All Level 1 parts of the missions can be "altered" by shooting the Galactic Away Team Shot. There are usually less shots on the PF after you make GAT, but they score exponentially more. Details are given in the corresponding sections of each mission.

General scoring seems to be (except for GAT, which scores higher):

1st mission shot: 100.000 points
2nd mission shot: 145.000 points
3rd mission shot: 190.000 points
4th mission shot: 235.000 points
5th mission shot: 280.000 points
6th mission shot: 325.000 points

Final shot: Each mission (except Nero) seems to have a final shot, indicating by alternating lights. The final shot scores more than all other shots.

Time to look at the modes in detail... MISSION DETAILS:

Prime Directive - Blue Shots

Phase I: All shots are lit blue. Making a shot advances towards getting a medal.

Phase I GAT: Galactic Lanes - After hitting one blue shot, GAT is lit. Making GAT lites the top rollover lanes as well the the two orbits feeding them for big points as well as adding 20 seconds to your missions time.

Phase I last shot: The right ramp is lit for the final shot.

Phase II: A time AND shot based round. You got 30 seconds to clear all lit blue shots (all shots are lit). You will also see a yellow/blue blinking shot. This shot scores more (it seems double). Failing to clear all shots in 30 seconds ends Prime Directive II without awarding it. To complete it you need to restart it by running the mode again - the game will remember all the shots you already completed.


Klingon Battle - Red Shots

Phase I: Left Orbit, Left Ramp, Warp Ramp, Right Orbit and Warp Ramp are lit. Making a shot advances towards getting a medal.  Once a shot is made it stays unlit for a specific duration or another relevant shot is made.

Phase I GAT: Galactic Ramps - After hitting one red shot, GAT is lit. Making GAT lights the left an right ramp alternately for huge points. 20 seconds are added to your time.

Phase I last shot: The left ramp is lit for the final shot.

Phase II:

Phase III:

Destroy the Drill - Light Blue Shots

Phase I: Left scoop, left orbit, left ramp and warp ramp are lit from the start. When making a shot, the shots retract to left by one shot, if you dont make shots, additional shots are lit to the right. The minimum amount of shots lit is Left Scoop and Left Orbit.

Phase I GAT: Galactic Spinner - After hitting one light blue shot, GAT is lit. Making GAT lights the left scoop and left orbit for huge points. Spins are worth 75k. 20 seconds are added.

Phase I last shot: The left scoop is lit for the final shot.

Phase II:

Phase III:

Nero - Purple Shots

Phase I: Left Orbit, Left Ramp, Warp Ramp, Right Ramp and Right Orbit are lit for Nero shots.

Phase I GAT: Galactic Targets - After hitting one purple shot, GAT is lit. Making GAT lights all black hole targets on the playfield for big points. 20 seconds are added.

Phase I last shot: There seems to be no final shot, all shots are equally lit.

Phase II:

Phase III:

Save the Enterprise - Green Shots

Phase I: Left Orbit, Left Ramp and Warp Ramp are lit for shots.

Phase I GAT: Galactic Warp Ramp - After hitting one green, GAT is lit. Making GAT leaves the left orbit and warp ramp lit for big points.

Phase I last shot:

Phase II:

Phase III:

Space Jump - Yellow Shots

Phase I: Left Orbit, Left Ramp, Right Ramp, Right Orbit are lit as shots

Phase I GAT: Galactic Vengeance - After hitting one yellow shot, GAT is lit. Making GAT for Space Jump is different, as it effectively disables all shots except the center shot for one final shot. Making on shot to vengeance immediately quits Space Jump. Not sure if this is a bug or not. 20 seconds are added.

Phase I last shot: The center shot is lit as a final shot.

Phase II:

Phase III:


Finishing 3 missions in a row awards The Captains Chair. Possible Captains Chair Awards are

Super Pops (left three missions) - Score 100 pop bumper hits to defeat Khan on the shuttle, each hit awards 90.000 points.

Super Spinner (bottom three missions) - Score 100 spins, each spin scores 75k.

Super Ramps (right three missions) - Score 9 ramp shots (left, right and warp are eligible), each ramp scores 700.000 points

Captains Chair awards don't have any time limit, they carry over from ball to ball, and are an easy source for points. Captains Chair modes end when you collected all necessary targets (spins, bumper hits or ramp shots, depending on the mode). You can have more than one Captains Chair mode running at any given time.


Finishing any mission three levels deep (eg its I,II and III part) will award a 2x multiplier on a specific shot for the rest of the game.

All Prime Directive modes: 2x Saucer
All Klingon Battle modes: 2x Left Ramp
All Space Jump modes: 2x Right orbit
All Destroy the Drill modes: 2x Warp Ramp
All Nero modes: 2x Left Orbit
All Save the Enterprise modes: 2x Right ramp


The TREK rollovers increase Spinner value by 10.000 points. The spinner value starts with 2.000 points on Ball 1, 4.000 points on Ball 2 and 6.000 points on Ball 3.

Increased spinner values do not carry over from ball to ball.


This multiball is a 3-ball multiball that can be turned into a 4-ball multiball by hitting the Black Hole target when lit. All shots are lit (in red) for Klingon Jackpots.

Jackpots are scoring starting from 200.000, and increase to 375.000, 750.000 and so on.

Super Jackpot - After making 6 jackpots, a super jackpot can be scored which is worth 6.25 million

Double super jackpot - scoring 6 more jackpots, a double super jackpot will be lit. The shot will travel around the playfield in a quick fashion. If you manage to hit the traveling shot, you will earn 20 million points plus a single gold medal.

Klingon Multiball ends when only one ball is left in play.


Vengeance Modes can be starting by hitting the center vengeance center target 5 times. Afterwards, the target stays down for a direct shot at the the vengeance.

There are 3 vengeance modes to be taken care of

  • Vengeance Multiball

    Shooting the vengeance holds the ball on the magnet. You get a second ball served - now a 15 second timer starts to hit the "captivated" ball and free it. Doing so will lead to a 3 ball multiball. If you dont free the ball in 15 seconds, the ball is released and you get a 2 ball multiball. You can get a 4th/3rd ball respectively by hitting the black hole target.

    Whether or not you manage to free the ball, you now get the chance to destroy the vengeance. Left Ramp, Right ramp and the vengeance shots are lit to fire photons at the vengeance. You can also use collected photon torpedos by hitting the lockbar button (see photon torpedos).

    Hitting the vengeance often enough will destroy the vengeance (on Premium and LE you will get a cool vengeance tilting effect), will award 5 million points (or 10 million while played as a combo).

    Furthermore, you get to play Victory laps. All shots are lit for points, finishing a round of shots scores big points (first round scores 1 million points, second 2 million,...) and relites all the shots.

    Vengeance Multiball ends when only one ball is left in play.

  • Vengeance Scoring

    A timed hurry up single ball mode. You need to score 5 shots at the vengeance while points are counting down. Making a shot resets points + 100k. Not making a shot till the points have reduced to 500.000 ends Vengeance scoring immediately.

    The sequence is:

    First Shot: Counts down from 1.000.000 to 500.000
    Second Shot: Counts down from 1.100.000 to 500.000
    Third Shot: Counts down from 1.200.000 to 500.000
    Fourth Shot: Counts down from 1.300.000 to 500.000
    Fifth Shot: Counts down from 1.400.000 to 500.000

    Making the fifth and final shot ends vengeance and immediately awards an Extra Ball. There is no extra score for finishing vengeance scoring.

  • Vengeance Battle

    5 hits to the vengeance target starts a "sudden death" mode. Hitting the target one more time leaves the target down for a few seconds. If you manage to get the ball back to the vengeance in those few seconds, you get 10% of your score as an award. The beauty of it - this shot can be doubled, or even quadrupled by combos and the the warp ramp playfield multiplier for a staggering 40% of your current score on top.

    Vengeance Battle ends when you make the shot or drain the ball. There doesnt seem to be a timer.


Photon Torpedos can be obtained by completing the 3 target weapon bank on the right (see playfield layout). Completing the 3 target bank award 3 photon torpedos up to a maximum of 8 torpedos, indicated by the yellow triangles in the middle. Torpedos are activated by pressing the lockbar button.

Torpedos can be used to:

  • Knock down the vengeance targets towards the start of a vengeance mode.
  • Score hits at the vengeance during the first vengeance mode.

Torpedos can NOT be used to:

  • Score the last hit of the first vengeance mode.
  • Can not be used to progress in 2nd/3rd vengeance modes.


On factory settings, the kickback is lit at the start of a ball, and can be re-lit by hitting the two shield targets multiple times. "Making" the kickback the first time scores 250.000 points


There seem to be two extra balls throughout the game. Extra balls, when lit, are collectible at the center vengeance shot.

Warp Ramp (see warp ramp) - A certain number of shots to the warp ramp light an extra ball. Factory settings make this is a self adjustable number, however, operators can set a fixed value as well. Mine adjusted to a value of 6, while starting as low as 3 or 4.

Finishing the second vengeance mode (see vengeance modes) - Finishing vengeance battle lites an extra ball, which you score instantaneously by hitting the center vengeance shot (eg last shot to finish vengeance battle also collects the EB).


Shooting the warp ramp repeatedly increases your warp level. You start out with Warp 1, and end at Warp 9.9. Shooting the warp ramp scores 250.000 (multiplied by 2x every time you hit the ramp in succession) points, and award multiple things:

  • At a dynamically adjusting (usually 6-7) or fixed warp level: Lite Extra Ball
  • At 9.1: Double Scoring for 60 seconds or ball drain, whatever happens first
  • At 9.9: Double Scoring + add-a-ball. Double scoring ends either after 60 seconds or when both balls are lost.

After reaching 9.9, you restart at Warp level 1. Reaching the Extra Ball level again won't award another EB on factory settings. For big points, try saving the 9.1 and 9.9 levels for big scoring modes, such as Kobayashi Maru, Enterprise Amok, 5 Year Mission, Klingon MB or any of the vengeance modes. This can make your scores skyrocket.


Throughout the game you can score other various combo shots for scores and some cool game quotes -

Kirk: Left Loop, Warp Ramp ("USS Enterprise, Captain James T Kirk commanding")
Bones: Left Loop, Left Ramp ("Dammit Jim, I'm a doctor, not a pinball wizard")
Sulu: Right Loop, Right Ramp
Uhura: Right Ramp, Left Ramp, Right Orbit
Spock: Left Ramp, Right Ramp, Left Loop, Warp Ramp

Info on combos taken partly from [2], TODO values and multiplier shots


The Black Hole target is lit by hitting the Black Hole/Red Matter targets multiple times. The awards from the black hole can be one the following:

  • Add more time
  • Add-a-Ball
  • Pop Bumpers score 200k (per hit - insane)
  • Score 200k
  • Increase Bonus Multiplier (?)

Add more time will usually be presented to you when you are running a mode, Add-a-Ball when you are playing a multiball.


For every mission you play, you can be awarded bronze, silver or gold medals. You earn medals by shooting for mission objectives. Medals score immediate points, BUT they score even bigger when you start one of the wizard modes. Making a gold medal immediately quits the mode by setting the remaining mode time to 0 seconds for a "Final shot". The final shot is usually worth more points if you hit the correct one (insignia alternating in two colors), except for Nero, which doesn't seem to have a final shot.

A single gold medal can also be scored by obtaining a double super jackpot from Klingon Multiball - see Klingpn Multiball for more details.

Making 3 shots awards a bronze medal, three more a silver medal and 5 more a gold medal. When playing a mission via GAT, different (mode specific, see Missions) rules apply.

Starting Kobayashi Maru awards medals as follows:

Set of 6 Bronze medals when starting Kobayashi Maru = 10M. Otherwise, each bronze is worth 1M up to a set.
Set of 6 Silver medals when starting Kobayashi Maru = 20M. Otherwise, each silver is 2M up to a set.
Set of 6 Gold medals when starting Kobayashi Maru = 35M. Otherwise, each gold is 3.5M up to a set.

Starting Enterprise Amok awards medals as follows:

Set of 6 Bronze medals when starting Enterprise Amok = 15M. Otherwise, each bronze is worth 1.5M up to a set.
Set of 6 Silver medals when starting Enterprise Amok = 30M. Otherwise, each silver is 3M up to a set.
Set of 6 Gold medals when starting Enterprise Amok = 50M. Otherwise, each gold is 5M up to a set.

TODO 5 yrs mission

Some info for medals and their values taken from [4].


There are at least 3 different skill shots in Star Trek -

  • Plunge the ball short so it doesn't hit the top rollover/bumper are, but instead trickles down to the upper right flipper finger. From there, shoot a warp ramp for "Warp Ramp Skillshot"
  • Hold the left flipper while either pushing the lockbar button or plunging the ball all the way so it hits the lower left flipper. This while lite a super skill shot at either the center vengeance target or the right ramp. The first super skill shot awards 1mil, consequent shots increase the super skillshot by 250k (?)
  • Hold the right flipper, full plunge - ball needs to hit the upper gate with enough force to reject it back out of the rollovers into right orbit, shoot warp ramp for a super skill shot worth 1.5 mil [3]


There a three wizard modes throughout the game - Kobayashi Maru, Enterprise Amok and Five Year Mission as the final mode. You qualify for a wizard mode by finishing a full level of missions (6 pieces, eg all level one missions, all level 2 missions...). This will lite the center vengeance shot to start your wizard mode. Before the wizard mode actually starts, you get awarded a big score for the medals you were awarded whilst battling out the missions.

Kobayashi Maru

After finishing the first level of all missions, the center shot will be lit for KM multiball. This is a two ball-multiball (can be made 3-ball by black hole award) has the following shots lit with their corresponding colors.

  • Left Saucer
  • Left Orbit
  • Left Ramp
  • Center vengeance
  • Right Ramp
  • Right Orbit

Notice that there are 6 shots lit? Thats right, thats as much as there are missions. Shooting the first shot of any lit shot awards XX, the second shot award the the amount of points you got from playing the corresponding mode up to a limit of 7 million points.

The mode ends when you are down to one ball or you managed to collect all awards (12 shots in total).

Enterprise Amok

After finishing the first level of all missions, the center vengeance shot is lit for Enterprise Amok. Enterprise Amok, again, starts out as a two ball multiball but can go up to four balls. It seems to be a switch based multiball, eg any switch counts towards your score and progression.

Five Year Mission









W?D: Fixing the slot reels reloaded

Problem: After my first attempt to fix the bloody Who Dunnit slot reels, the rightmost reel started acting up again recently - it spins freely, but stops after one or two turns max.

Solution: Checking into problem, i noticed that the slot index opto of the right slot reel wasnt registering. Time to have a look at the switch matrix.


As we can see, two wires (ORG/GRY, which is in reality WHT/GRY and GRN/YEL) are involved. Connecting the wires from the right index opto to the middle opto didnt change anything either, so that ruled out the opto board itself. Following the wires, a broken cable was discovered on the WHT/GRY wire at the BLACK target. Soldering the wire back to the target fixed the issue. Problem solved.

WPC Anti Ghosting Eproms

Issue: In all modern pinball machines (WMS/Bally), the use of LED's usually leads to ghosting, a condition where other LEDs also are lit or flickering while they shouldn't be.

Solution: While there are special non-ghosting LEDs out there, these are expensive and just not needed. The issue stems from a timing problem within the lamp driver code when using LED's instead of conventional light bulbs.

Luckily there's an easy fix - and its called WPCLP (WPC Lamp Patcher), and was kindly made available on GitHub by Eric Conner, programmed by John Honeycutt -

This utility basically takes an existing WMS/Bally WPC ROM and modifies the lamp driver code to behave with modern LED's. If you want to try it for yourselves, pull a copy off of github, compile on your favorite platform (i'm using gcc but mingw should work just fine) and give it a spin.

Here's a quick snap of it in action:


Take that patched ROM file (in that case a T2), burn it, and you are good to go. If you don't want to do the work, feel free to contact me for any EPROM needs you might have.

W?D: Fixing the slot reels

Issue: On Who Dunnit, the slot reels are either stuck, move only sometimes, or are just jittering.

Solution: First of all determine if the problem is of mechanical or electrical nature. If you have one working reel, try to swap the driving pcb around between the working and the non working one. If the reel is now working, you have an electrical issue.

If you find your issue to be mechanical - the motors are prone to failure due to dirt. Instead of buying new ones, just clean the old ones - a detailed instruction guide is available here -

If you find your problem to be electrical and have ruled out the usual - no voltage, connectors, opto not working... - then there's a good chance of the LM339 being faulty. For whatever reason the LM339's on these boards seem to fail quite commonly.

Happy Slotting!




F 14: Gen' Yagov slingback not working at all

Issue: The General Yagov kicker is not working at all. This part adds a lot of playing fun (the kicker slams the ball back brutally to the player), so seeing it work would be nice.

Solution: At that time, Williams didnt use any TIP36c transistors to drive high power coils. They used regular TIP 122 transistors to drive whats called a "snubber board" - many variations starting with C-11232. The snubber board, basically a relay, would then energize and complete the groundpath for 50v to drive a high power solenoid.

Heres a picture of a snubber board -


Furthermore, there are no schematics of the snubber boards around in the official manuals. One gentleman from german draw one a while back -


Suspecting the Snubber board to be the most likely culprit, i swapped it with a known good one - nothing. You could hear the relay clicking, but thats about it.

Next check was to make sure that 70v are actually there. Hold one lead of the DMM to GND, the other one to +70v lug, and 70v was there. Last thing to check was the coil and the wiring to the coil itself. Getting to the coil itself is a real p* in the ass, basically all of the ramps have to go. Once there, the coil was taken out and measured. An intact coil for that location should measure around 4 ohms, the one i had measured around 3 megaohms - the coil was basically open. Replaced with a known good coil brought the kicker back to live.

Issue resolved.

Data East Star Wars - DMD showing mostly garbage, but a few scenes render ok

Issue: The DMD is showing either all dots lit, or garbage. Sometimes it would show some scenes correctly, but most of the time garbage is displayed.

Solution: Changed the display roms to known good roms, nothing. Decided to remove the custom PALs and the memory ic (a 62256) to give the legs a good cleaning. While removing the memory ic, i noticed two bent (!) legs under the ic - whoever did this certainly never tried it afterwards.

Trying to straighten out the legs broke them off. Cut off two legs from a junk ic, soldered them on and put the ic back into the socket. DMD is now fine. Issue resolved.

Data East Star Wars - +5 volt missing/low

Issue: +5v is missing/low at +0,9v, therefore no CPU boot, nothing. The +12 and -12v are fine.

Solution: According to the schematics (link), the components responsible for +5v generation are IC1 (an MC1723CP) and TR5 (2N6057, the transistor on the huge cooling block). Changed both with known good parts, but the +5v were still at 0,9v. As these boards are all 20+ years old, looking for leaked or bulged caps is always a good idea - but visually they all looked good. I decided to desolder the caps one by one and measure them with a capacitance meter.

Started with C2 which is right after the bridge rectifier which should be a 100uf 25v cap. Once desoldered, you could see a tiny bit of leakage on the bottom side of the cap - this is unusual, because caps usually leak on the top. Sure enough, the cap measured between 6uf and 10uf. Replaced with a 100uf 35v (higher voltage is okay), and +5v are right back. Issue resolved.





Demolition Man - Row 6 of switch matrix not registering

Issue: The sixth row of switches on DM was not registering at all. A fault on the CPU was suspected, as it was recently cleaned of battery leakage damage.

Solution: Responsible for row 6 is the white-blue wire, as per ops manual -


Looking at the schematics for the wpc-89 cpu board, we see the following components involved coming from J209-7 -


We can see J209-7 to D8, cont to R61/R62, to a LM339 at pos U19 pins 8,9 with an output at pin 14, cont to LS240 at U13 pin 4 and R32.

Using an DMM, checking for continuity as by the abovementioned path revealed a bad trace between U19 pin 14 to R32 and U13 pin 4. Soldered a wire jumper from U19 pin4 to R32, switches are now registering. Issue resolved.


Monster Bash - all flasher are really bright and capacitor C10 explodes

Issue: On Monster Bash, all flashers are really bright and fail after a couple of flashes. Furthermore, after 10 minutes of running, smoke comes out of the backbox and C10 on the PDB explodes.

Solution: Checked for voltage on flasher sockets and found +50v instead of +25v. The cap in the 25v section is rated for 35v, therefore exploding when prolonged 50v were applied to it. Found that a previous owner attached the power wire for flashlamps to 50v instead of 25v.

Cleaned exploded Cap, replaced C10, and connected flashlamps to the proper 25v power wire. Issue resolved.

BK2K - a display segment is stuck on

Issue: On a Black Knight 2000, a display segment is always lit.

Solution: Tried the display board in another machine, which showed the same error, therefore isolating the error to the display board. Looked at the manual for the corresponding segment (see below - segment "m"). Probed the corresponding UDN7180A (U16 - 12) with a logic probe and saw the output signal was stuck for the affected pin. Probed the input pins of the UDN7180A, and they were pulsing correctly.

Replacing the affected UDN7180A solved the issue.




Judge Dredd - flippers weak, even after a full mechanical rebuild

Issue: On JD, even after a full flipper rebuild, the flipper fingers feel weak.

Solution: Checked for correct components and correct coils, ok. Measured voltage coming to coils, which should be around 70v dc when no flippers are pressed - only got around 55v at the coils.

On JD, power for the flipper fingers is generated via a bridge rectifier (br1) on the fliptronics board, with AC power coming directly from the transformer's secondary winding to j901. Measured the bridge's diodes - all ok, voltages at j901 were ok as well.

Looking at the board, C2 was missing, which Williams did on some boards, and installed on others. Installing C2 on the board (i used a 100uf 100v axial capaciror) bumped the voltage right up to around +68VDC. Flippers were now snappy and powerful. Issue resolved.


Monster Bash - all motor driven gadgets no longer working

Issue: All motors are no longer working (Frank up/down, target bank up/down, dracula)

Solution: Expected the +12v to be missing for the motors, measured, but 12v was there. Probed the upstream ic's on the power driver board with an osciloscope, and found that the output pins were not pulsing. Probed the input pins for pulses, found that they were not pulsing either. Those pulses are supposed to come from the CPU.

On a hinch i reseated the short ribbon cables between CPU and the Power Driver a couple of times, and motors started working again. Issue resolved.

TAF - Settings are not being retained

Issue: Occasionally, on startup, TAF would present a factory settings restored message. This wouldnt happen everytime, but often enough to be annoying.

Solution: Easy things first - removed battery holder, soldered in new external battery holder with new batteries, issue still persistent. Checked for 4,5v at RAM chip U8 at pin 26,27,28 - measured ok. Changed RAM chip at U8 with known good 6264 - issue still present. Checked for 4,5v again - it was reading 0,xx suddenly. Tapping the diode with the finger at position D2 restored the 4,5v sometimes, sometimes not. 

Seems that D2 had some whacky internal fault which causes it to react on vibration, and tapping it caused it to fail at times. Replaced D2, issue resolved.

TAF - Enter Test Menu button not working

Issue: Cannot enter test menu on TAF, button not registering.

Solution: Checked actual button, measured ok. checked wirking for broken cables, measured ok. As the the test menu button is a dedicated switch, used alligator clips to jumper the pins directly on the CPU (j205), button still not registering, therefore isolating the fault to the CPU.

Measured the way up to the logic ic's from j205 and found a broken trace not visible with the bare eye, propably a leftover from a previous battery damage repair. Soldered a jumper wire, button is now working.

Lord of the Rings - game would reset after some time

Issue: Lord of the rings resets mid-play, sometimes at start, sometimes after hours of play.

Solution: Checked voltage on CPU, found it to be 4,9 volts. Reseated all relevant power cables on cpu and power supply, still 4,9 volts. Used the poti R116 on the power supply to raise the voltage to 5,1 volts. Issue never occured again.


(picture taken from

Home ← Older posts