Force II (Gottlieb, 1981): faults and System 80 replacement boards

June 25, 2026

Is your Force II pinball by Gottlieb (1981) reading far too high after a power supply rebuild, dropping out on the game over relay, refusing to boot, or showing weak and blank displays? On a Gottlieb System 80 machine these symptoms have a short list of usual suspects: the power supply regulation, the connectors, the grounds, and the ageing CPU and Driver boards. Here is what owners actually find on this game, including the one component that explains the classic 60/42 V complaint, and the System 80 replacement boards that fit it.

About Force II (Gottlieb, 1981)

See it: full photo gallery for Force II on IPDB

Force II shipped in February 1981 as Gottlieb model 661, a widebody System 80 game on a combat-and-aliens outer-space theme — the backglass is remembered for its distinctly odd-looking aliens. It was designed by John Osborne, with art by David Moore, and about 2,000 units were built.

What makes it unusual on the playfield is how much drop target there is: two five-bank drop target banks plus a four-bank, fourteen targets in all, alongside four flippers, three pop bumpers, a kick-out hole, a roll-under spinner and a ball kicker. The spinner feeds the lock that starts the game's two-ball multiball, which matters when you are fault-finding — see below.

Force II pinball machine, Gottlieb 1981 — Force II (Gottlieb, 1981) — a System 80 widebody, model 661.

Manufacturer: D. Gottlieb & Co.
Release: February 1981
Model number: 661
Production run: approx. 2,000 units
Design: John Osborne
Art: David Moore
Electronic system: Gottlieb System 80
Cabinet: widebody, 4 players, approx. 260 lb (118 kg)
Playfield: 4 flippers, 3 pop bumpers, two 5-bank drop targets, one 4-bank drop target, kick-out hole, roll-under spinner, ball kicker
Multiball: 2-ball
Latest software: 661/2
IPDB: machine #916

Survivors are thin on the ground. The Vintage Arcade Preservation Society census recorded through Museum of the Game ranks it 2 out of 100 for how often it is seen, with only three known original machines among active members. Pinside's estimate for a working example sits around $1,480–$1,720, with a median asking price near $1,600 — a guide rather than a valuation, since condition dominates.

What is actually inside a System 80 backbox

The System 80 CPU board is built around a 6502 processor with a 5101 static RAM at Z5 and three 6532 RIOT chips at U4, U5 and U6; the game EPROM sits at U3. The supporting logic includes Z1 (4528), Z2 (7474), Z3 (7404) and Z4 (4081). A RIOT combines RAM, input/output and a timer in one package, and since the three of them share switch and lamp duties, one failed RIOT can silence a whole group of switches while the game otherwise looks healthy.

The NiCad battery sits on that same CPU board. It leaks, and the electrolyte tracks along the board — often under the chip sockets, where it does its damage out of sight.

Common faults on Gottlieb System 80

Battery corrosion on the CPU board. Remove the battery and neutralise the residue before anything else. Assume trace damage until you have checked.
Grounding. System 80 left the factory under-grounded. The ground mods bond CPU, Driver, power supply and sound boards properly and cure many random resets.
Connectors. Oxidised Molex pins, particularly the CPU-to-Driver link. Re-pin rather than scrape.
Displays. Missing segments, blank digits, or digits locked on — usually the card-edge connectors.
Slam switch. Dirty or mis-set, it stops the game at start-up and impersonates a board fault.
Power supply. Tired regulation and out-of-tolerance reference components.

Battery corrosion on a Gottlieb System 80 CPU board — Typical corrosion from a leaked NiCad battery on System 80 — neutralise it first.

Force II-specific issues owners report

High 60 V and 42 V rails after a power supply rebuild — and the part that causes it. This is the signature Force II complaint, and it has a precise answer. An owner on Pinside rebuilt the A2 power supply board and found both rails roughly 9 V high: the 60 V rail reading 69 V and the 42 V rail reading 51 V. The cause was the 62 V zener diode at CR5. On this supply the E2 voltage sets the output from the Q1 pass transistor, with the output following roughly the base voltage minus 0.7 V. CR5 carries a ±5% tolerance, and when it drifts high — E2 measured 70 V instead of about 63.6 V — every rail downstream rises with it. The fix was to replace CR5 with a fresh 1N4759A zener. If your rebuilt Force II supply reads high across the board rather than on one rail, check CR5 before you suspect the transformer or Q1.

Coils that fire repeatedly for a mechanical reason. On a documented Force II restoration, a kick-out coil that kept re-firing turned out not to be an electrical fault at all: a bent lamp socket was fouling the plastic lever on the mechanism and holding the switch made. Repositioning the socket fixed it. Before you go hunting a shorted driver transistor for a repeating coil, look at what is physically touching the mechanism.

Ball kick-out seized with old grease. The same restoration found the kick-out mechanism "locked up solid" from decades-old hardened grease. A clean and reassembly restored it. A dead kick-out is worth checking mechanically before electrically.

Slingshot switches half-wired — and the boards are innocent. That restoration also found only one of the two switches working on each slingshot, with wires simply missing from the second switch and needing to be rewired. Worth knowing alongside a key System 80 fact: the slingshots are not CPU-controlled on this platform; they are directly powered like an electromechanical game. A dead slingshot is a switch, coil or wiring problem, never a Driver board problem.

Multiball that will not start — check the spinner switch. Because the roll-under spinner feeds the lock, a spinner switch that misses slow spins will stop multiball from triggering even though the game plays normally otherwise. The restoration notes record exactly this: the under-playfield spinner switch needed adjusting so slow hits registered.

Fuses that keep blowing — look for broken bulbs. Repeated fuse failures on that game traced to two bulbs with the glass missing, shorting the lamp circuit. Corroded and slack fuse clips were also found and needed buffing and tightening; a loose clip causes heat and nuisance failures of its own.

Apron display blank while the player displays work. The ball-in-play and credit display in the apron going blank while all four score displays behave is a reported pattern. Treat it as its own connector and display problem rather than evidence of a sick CPU board.

Drop target plastics. With fourteen drop targets, this game wears its target plastics. Broken and warped targets were found and repaired on the restoration, and a stuck-closed drop target switch behind a bank will confuse scoring until the plastic is sorted out.

Game over relay. Temperamental relay contacts are a familiar early-solid-state complaint; clean and adjust them rather than replacing parts speculatively.

Replacement boards that fit Force II

Force II is a System 80 game, so the System 80/80A/80B family applies:

GottFA80_Plus (Light) — all-in-one CPU + Driver + power supply board, without sound.
GottFA80_Plus (Full) — the same with an integrated sound board.
Gosof — replacement sound board.
Godri80 — replacement Driver board.
Lisy80 — CPU board with web-based diagnostics.
GoPOP80 — pop bumper driver board (replaces MA-922 / A-19741).

Given that the defining Force II fault is power supply regulation, an all-in-one board that brings its own supply removes the CR5 adjustment problem permanently rather than re-treating it. The boards are battery-free, so corrosion does not return, and they use non-volatile memory, so settings and high scores survive a power-down.

About Lisy: LISY is an independent developer's free, open DIY project for running Gottlieb machines on a Raspberry Pi, documented at lisy.dev. We neither created nor maintain it; we supply the board and credit the project.

GottFA80_Plus all-in-one board for Gottlieb System 80 — The GottFA80_Plus: CPU, Driver and power supply on one board, with no battery.

Installation is Plug & Play — a few minutes, no soldering. We test every board before it ships and support it afterwards, with tutorials and free help if you need it. Get in touch if you are unsure which board your game needs.

Step-by-step diagnosis

Power off, look first. Inspect the CPU board for battery residue and corrosion, including under the chip sockets. Remove the NiCad battery if still fitted.
Check the rails. If the 60 V and 42 V rails read high together after a rebuild, measure E2 and check the CR5 zener before anything else.
Measure on the right range. Transformer outputs are AC; reading them on a DC range gives misleadingly low figures. Pull fuses to unload the supply when measuring.
Do the grounds. Apply the ground mods between CPU, Driver, power supply and sound boards.
Re-pin the connectors. Especially the CPU-to-Driver link.
Displays. Never plug or unplug a display with the power on. Clean the card edges, reseat, and test with a known-good display.
Mechanical check. Kick-out freedom, slingshot switches, spinner switch, drop target banks and their plastics.
Final test. Boot, credits, displays, coils, and multiball via the spinner lock.

FAQ — Force II (Gottlieb, 1981)

My Force II power supply reads 69 V and 51 V after a rebuild. What is wrong?
Almost certainly the 62 V zener at CR5 drifting out of its ±5% tolerance. E2 sets the output from Q1, so a high E2 lifts every rail. Replacing CR5 with a 1N4759A is the documented fix.

My Force II will not start. Where do I begin?
Battery corrosion on the CPU board first, then the grounds, the connectors and the slam switch, before suspecting the boards.

A coil keeps firing repeatedly — is the driver transistor shorted?
Check the mechanism first. On one documented Force II, a bent lamp socket fouling the plastic lever held the switch made and caused exactly that symptom.

Multiball will not start on my Force II.
Check the under-playfield spinner switch. The roll-under spinner feeds the lock, and a switch that misses slow spins prevents multiball from triggering.

My fuses keep blowing. What should I look for?
Broken bulbs shorting the lamp circuit are a documented cause on this game, along with corroded or slack fuse clips that need buffing and tightening.

How many Force II pinballs were made?
About 2,000, in February 1981, as model 661. Few survive — the VAPS census lists only three known original machines among active members.

How much is a Gottlieb Force II worth?
Pinside estimates roughly $1,480–$1,720 for a working game, with a median asking price near $1,600. Condition drives the real figure.

A slingshot is dead — is it the Driver board?
No. On System 80 the slingshots are not CPU-controlled; they are directly powered. Check the switch blades, coil and wiring.

Sources & further reading

Own a Force II? Send us a photo and we'll add it here with credit — get in touch.

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