Pinball electronics explained: MPU, driver, power supply and sound board
The electronics of a pinball machine rely on four master boards: the MPU (the processor), the driver board (which controls coils and lamps), the power supply board (which generates the voltages) and the sound board. Understanding what each one does lets you diagnose a fault in minutes and choose the right repair. This complete guide explains the electronics of a solid-state pinball machine, board by board, with failure symptoms and modern Plug & Play solutions.
Contents
- The 4 master boards of a solid-state pinball
- The MPU board: the brain of the pinball
- The driver board: the muscle that controls coils and lamps
- The power supply board: the source of every voltage
- The sound board: giving the pinball a voice
- Diagnosing an electronic fault board by board
- Repair or replace: Plug & Play FPGA boards
- FAQ
The 4 master boards of a solid-state pinball
From 1977 onwards, pinball machines abandoned electromechanical relays for digital electronics (these are called "solid-state" pinballs). Whether Gottlieb (System 1, then System 80/80A/80B), Williams (System 3 to 7) or Bally/Stern (1977-1985), the logic stays the same: a set of boards shares the tasks. Some machines combine several functions on a single board, others split them out, but you always find these four major roles.
| Board | Main role | Typical failure symptom |
|---|---|---|
| MPU (CPU) | Brain: runs the game rules, reads switches, drives the outputs | Pinball won't boot, resets in a loop, erratic behaviour |
| Driver | Muscle: activates coils, controlled lamps and flashers on the MPU's command | Stuck coil, dead lamp, target that no longer works |
| Power supply | Source: turns AC into regulated DC voltages (+5 V, etc.) | Blank display, restarts, whole machine stays dead |
| Sound | Voice: receives an order from the MPU and plays the requested sound or speech | No sound, permanent noise, missing speech |
Good news: unlike the mechanics of the playfield, the electronics of a pinball machine are now fully replaceable with modern boards. Let's look at each board in detail.
The MPU board: the brain of the pinball
The MPU (Main Processing Unit), also called the CPU board, is the brain of the machine. Once booted, it controls the lamps, coils, sounds and score display, and reacts to the switches of the playfield and cabinet by generating the matching outputs. It contains the microprocessor, the ROM (EPROM) that stores each game's specific rules, the working RAM and a reset circuit that initialises the board at start-up.
The MPU's curse: the battery. On Gottlieb System 80 machines, as on many pinballs of that era, a battery powers the memory to keep settings and high scores when the machine is off. Over time the battery leaks and releases a corrosive electrolyte that attacks the board and its components — sometimes with no visible leak. The corrosion destroys traces and memory (the famous 5101 chips on System 80), and a corroded MPU becomes unrepairable. That's why a leaking battery is the number-one cause of death for a CPU board. We cover it in a dedicated guide: the leaking battery on a pinball.
Symptoms of a failing MPU: the pinball won't boot, restarts in a loop, shows a frozen score, locks up mid-game or ignores certain switches. On early System 80s (from Spiderman to Haunted House), an MPU crash could leave a coil or a display energised and damage other components: hence the value of a reliable reset circuit.
The driver board: the muscle that controls coils and lamps
The driver board (or control board) receives the MPU's commands and turns them into physical action. It is made up mainly of transistors, resistors and diodes, plus a few integrated circuits that interpret the MPU's signals. An important and often misunderstood point: on an electronic pinball, power is always present at the coil terminals. The transistors on the driver board do not switch a coil's power off: they complete the path to ground to activate it. It's a subtle but essential nuance for any troubleshooting.
The driver board generally handles a "high power" section (strong coils, up to 50-70 V) and a "low power" section. It also often drives the controlled lamps, wired in a matrix to limit the number of wires and transistors: a few dozen wires are enough to control dozens of bulbs.
Symptoms of a failing driver board: a coil stays stuck (often a blown transistor), a target or pop bumper no longer reacts, a controlled lamp stays dead. On Gottlieb System 80s, the classic problems of the original driver are corroded connections to the MPU, hard-to-find MPS-U45 transistors and 2N3055 transistors that eventually burn holes through the PCB. Note: the absence of the –12 V rail is a common cause of stuck coils. Always separate the electronic fault from the mechanical fault: a stuck drop target or an ejection-hole contact left closed is not a board defect.
The power supply board: the source of every voltage
The power supply board takes the AC voltage from the transformer and converts it into usable DC voltages. Bridge rectifiers turn AC into DC, capacitors filter and smooth, and regulators set the exact values. The +5 V DC powers the logic boards and must be perfectly regulated: if the +5 V drops below 4.8 V, the MPU almost certainly runs into trouble. The score displays require high voltages, and some sound boards need 12 or 20 V.
Symptoms of a failing power supply: a completely dead machine, unwanted restarts, flickering displays. On Gottlieb System 80, the small +5 V supply has a reputation for fragility: its adjustment potentiometer gets dirty and struggles to hold 5 V, and the lack of a "crow bar" circuit means that a failure of the LM338K regulator can send a destructive overvoltage to the other boards. Diagnostic tip: if voltages drop by more than 15 %, a display is probably short-circuited — disconnect all displays (machine off), then reconnect them one by one to locate the faulty one.
The sound board: giving the pinball a voice
The sound board is an independent circuit that receives a limited order from the MPU ("play sound 1, 2, 3…") and carries it out. It includes a section that processes the MPU's signal, a section that generates the sound (a simple tone generator on early games, or EPROMs holding samples and speech synthesis on later models) and an amplifier, with its own voltages, connected to the speaker. On Gottlieb System 80B, speech synthesis is part of the play experience.
Symptoms of a failing sound board: no sound at all, continuous or crackling sound, missing speech while the effects still work, or the opposite. Like the other boards, it ages: tired capacitors, oxidised connectors, a failing dedicated supply.
Diagnosing an electronic fault board by board
The first move is to identify which board is at fault before dismantling anything. This table links the symptom to the most likely board:
| Observed symptom | Most likely board |
|---|---|
| Completely dead machine, blank display | Power supply (then MPU) |
| Reset loop, frozen score, crashes | MPU (often battery corrosion) |
| A coil stays stuck | Driver (transistor) or –12 V |
| A controlled lamp or a target no longer responds | Driver (matrix / transistor) |
| Flickering display, unstable voltages | Power supply or short-circuited display |
| No sound or no speech | Sound board |
A dedicated diagnostic tool saves precious time. On Gottlieb System 80/80A/80B, the Lisy80 board sits in place of the MPU and lets you test lamps, coils and switches one by one to quickly isolate the failing part. To go further, read our guide to boards for Gottlieb System 80 and the System 80B guide.
Repair or replace: Plug & Play FPGA boards
Faced with a corroded or unstable original board, two paths exist: component-by-component repair (time-consuming, and impossible if the traces are eaten away) or replacement with a modern board. At Pinballs Store, every electronic function has an FPGA replacement board faithfully reproducing the original behaviour, battery-free (so no more corrosion) and Plug & Play (same connectors, no soldering):
- All-in-one MPU: the GottFA80_Plus replaces the System 80/80A/80B MPU and also redoes grounds and power supply.
- Driver board: the Godri80 replaces the original System 80 driver board.
- Sound board: the Gosof (with speech) restores sound and voice.
- Pop bumper driver: the GoPOP80 replaces the MA-922 / A-19741 boards.
- Williams System 3-7: the WillFA7 — see the Williams guide.
- Bally/Stern 1977-1985: the BallyFA — see the Bally/Stern guide.
To weigh repair against replacement based on your machine's condition, read our article: repair or replace a pinball electronic board.
Replace your Gottlieb System 80 electronics without soldering
The GottFA80_Plus replaces the System 80/80A/80B MPU board and redoes the original grounds and power supply. Plug & Play (same connectors), battery-free (no more corrosion), 15-day warranty and free technical support in French.
From 349 € — Discover the GottFA80_Plus → (V2 Full version with integrated sound board at 399 €)
FAQ: the electronics of a pinball machine
What are the electronic boards of a pinball machine?
A solid-state pinball has four major boards: the MPU (CPU) board that runs the game, the driver board that controls coils and lamps, the power supply board that generates the DC voltages, and the sound board. Depending on the machine, these functions may be combined or split across several circuits.
What does a pinball's MPU board do?
The MPU board is the brain of the pinball. It runs the game rules stored in EPROM, reads the playfield switches and drives the lamps, coils, sounds and displays. If it fails, the pinball won't boot or behaves erratically.
Why does my coil stay stuck?
A stuck coil most often comes from a blown transistor on the driver board, or from the absence of the –12 V rail. Be careful to distinguish: if it's a mechanical contact left closed (a dropped target, an ejection hole), the problem is not electronic.
My pinball's battery leaked — is my board dead?
Not always, but the electrolyte corrodes traces and memory and can make the MPU unrepairable. If the corrosion is advanced, replacing it with a modern battery-free board is the most reliable solution. Clean it and assess the damage before deciding.
Can you replace a pinball board without knowing how to solder?
Yes. Plug & Play FPGA boards use exactly the same connectors as the original boards: you simply unplug the old board and plug in the new one, with no soldering at all.
Does a replacement board fix all the pinball's problems?
No. A modern board replaces the electronic part (MPU, driver, power supply, sound) but does not fix mechanical faults: rubbers, worn contacts, dead coils, targets or mechanisms. A diagnosis always separates the electronics from the mechanics.
