The 15 questions that arrive most often in the site's email, with short answers and pointers to the detailed articles. They apply to solid state pinball machines of the '80s and '90s (Williams, Bally, Gottlieb, Data East, Stern), unless stated otherwise.
First the basics: 99% of the time a pinball machine that doesn't work can be repaired. These machines were built to run 16 hours a day and to be repaired with a screwdriver and a multimeter. Before you open the backbox, read question 14 about safety.
1. It powers up, lights up, but won't start a game
The machine has power and lighting but the Start button does nothing. Check in this order:
- Credits. Most games need a credit to start. Set it to free play in the settings or press the coin mech switch by hand.
- The ball. If there is no ball in the outhole (or in the trough on newer machines), the game thinks the ball is still in play. Check that the outhole switch closes.
- Tilt. A stuck tilt switch or slam tilt switch (on the coin door) blocks the game.
- The Start switch. Dirty contacts or a broken wire. On Bally machines, if the MPU hasn't booted properly (see question 11) the Start doesn't work.
- Test mode. Enter the diagnostics from the coin door and see whether the machine "sees" the switches.
2. It doesn't power up at all
Start from the simplest and work towards the hardest: the wall socket and the power cord, the main switch under the cabinet, the main fuse next to the transformer, the coin door safety switch (interlock) on newer machines. Measure whether power reaches the transformer. If it does, measure the fuses on the power supply board one by one, pulled out of their holders, with the multimeter on continuity. A fuse can look good and still be blown.
3. It blows the same fuse again and again
Do not fit a bigger fuse. The fuse is doing its job: something is drawing too much current. The usual culprits, depending on the circuit:
- Coil fuse: a shorted diode on a coil, or a coil burning out because it stays energised (see question 7). Disconnect the coils group by group to pin it down.
- Power supply fuse: a shorted bridge rectifier or capacitor on the power supply board.
- GI lamp fuse: a short in a lamp socket or in a wire that has melted from heat.
- Flash lamp fuse: the wrong lamp (e.g. #89 instead of #906) or a stuck transistor.
4. It resets in the middle of a game
Usually when many coils fire together, e.g. during multiball. The cause is almost always a drop in the +5V logic voltage. Measure the +5V on the MPU while the game is playing: below 4.9 V is a problem. The causes, in order of frequency: burnt or loose connectors between the power supply and the MPU, an aged bridge rectifier, a dried-out filter capacitor, a tired voltage regulator. On WPC machines this is the classic "WPC reset". See the article Tools and measurements for the correct values.
5. The display is half dark or digits are missing
Three different faults that look alike:
- One segment missing on all digits: a transistor or resistor of the segment driver on the display board or on the MPU.
- A whole digit missing: digit driver or the display itself.
- Everything dim, reddish, with "smoke" at the edges: the gas plasma display has aged (outgassing). It can only be fixed by replacement. There are modern LED displays for all systems, which also draw less current.
- Everything dark: the high voltage for the displays (100 to 190 V depending on the system) is missing. A fuse or transistor in the high voltage section of the power supply.
6. The flipper is weak
The most common mechanical question. In order of likelihood: a worn plastic coil sleeve inside the coil, a worn plunger and link, a burnt or misadjusted end-of-stroke (EOS) switch on machines made before 1990, a dirty cabinet button switch, a hardened rubber on the flipper. If both flippers are weak together, measure the coil voltage: low voltage means the bridge rectifier or a capacitor in the power supply. The full rebuild is described in the article Maintenance: playfield, rubbers, flippers.
7. A coil stays locked on and gets hot or smokes
Switch the machine off immediately. A coil that stays energised burns out in a few seconds and can take the transistor with it. The cause is almost always a shorted driver transistor on the driver board. Measure it with the multimeter in diode mode: a good transistor does not conduct in both directions. Replace the transistor, and check the pre-driver transistor and the coil diode too. See the article Repair guides by system: Williams 3-7, Bally, System 11, WPC for which transistors each board has.
8. A whole row of lamps doesn't light
The controlled lamps are in a matrix (lamp matrix) with rows and columns. If a whole row or column is missing, the problem is in its driver (a transistor, or an SCR 2N5060 on Bally machines) or in a connector. If only one lamp is missing, it's the lamp or the socket. If the general illumination (GI) doesn't light in one area, look for a blown GI fuse or a burnt GI connector on the power supply: it's the most classic fault on System 11 and WPC.
9. There is no sound or it makes noise
Check the volume potentiometer (inside the coin door), the speaker connector and the speaker itself. Then the voltages of the sound board, especially the -12 V that tends to get forgotten. A constant hum usually means dried-out capacitors on the sound board. If there is no sound at all and the voltages are correct, it's a ROM or the amplifier.
10. Some switches don't work, or trigger on their own
The switches are also in a matrix. One switch that doesn't work: dirty or open contacts (clean them with a piece of business card, not sandpaper, and adjust the gap). Many switches in the same row or column: a connector or a driver on the MPU. Switches that "close" on their own when you press another one: a failed diode on some switch in the same row. The test mode shows immediately which switches appear closed.
11. It loses the settings and scores, or on a Bally it doesn't do the 7 flashes
The batteries on the MPU keep the memory. On Bally -17/-35 boards the NiCad battery is soldered onto the board and leaks, eating away the copper traces: if it hasn't been removed already, remove it today. The MPU LED must flash 7 times at power-up; if it stays on or stops earlier, the MPU has a problem (usually corrosion or the 5101 RAM). On Williams and WPC machines the 3 AA batteries need changing every year, and it's better to move them to an external holder away from the board.
12. Where do I find manuals and schematics
Almost everything is available free online: the IPDB (Internet Pinball Database) has photos, flyers and often the manual for every machine.
13. The playfield is worn or the inserts have lifted
Wear in the artwork is a cosmetic matter and doesn't affect the game, unless the wood has been eaten away around inserts or holes. Small wear is fixed with touch-up and clear varnish, while a mylar or a patch of clear coat protects the areas that wear. A full playfield restoration is weeks of work. See what was done on the Blackout in the collection.
14. What do I watch out for, for my own safety
- Unplug the machine from the wall before you touch anything. The switch is not enough.
- The displays run on 100 to 190 V DC. The high voltage capacitors hold a charge even after the machine is switched off. Don't touch the back sides of the displays and the power supply with the machine on.
- Measure with one hand. The other one in your pocket.
- On old machines the power cord and the line filter are 40 years old. Replace them.
- Lift the playfield carefully and prop it up. It weighs quite a bit and drops suddenly.
15. Can you come and look at it? Do you sell parts?
The site is a hobby, not a business, and I don't sell parts. I'm happy to help by email anyone who is trying to repair their machine themselves: send photos, the model, and exactly what it does or doesn't do, through the Contact page. Sometimes I'm slow to reply because of the day job, a little patience.