Pinball (Stern, 1977): faults and replacement board (Stern M-100 MPU)
Is your Stern Pinball (1977) dead on power-up, showing a stuck diagnostic LED, locking up at switch-on or producing erratic scores and displays? These symptoms point to an ageing Stern M-100 MPU, most often a victim of battery corrosion. Here are the most common faults and the compatible replacement boards.
About the Pinball (Stern, 1977)
“Pinball” is the very first solid-state machine from Stern Electronics, released in late 1977. It was also the first design fully created by Stern after taking over Chicago Coin. With 1,654 units produced, it shares its ROM with the Stingray that followed, while offering a different playfield and target layout.
- Manufacturer: Stern Electronics
- Year: 1977
- System: Stern M-100 MPU (architecture derived from Bally / Stern)
- Type: solid state, 4 players, 2 flippers
- Theme: classic “pinball” machine with abstract artwork
Common faults (Stern M-100 MPU)
The M-100 generation, shared by Bally and Stern from 1977 to 1985, has well-known weaknesses:
- Battery corrosion: the battery soldered to the MPU eventually leaks and eats away traces, IC sockets and nearby components (the U8 area is especially exposed).
- Boot lock-up: a temperamental “reset / valid voltage detection” circuit, especially with a modern switching power supply instead of the original linear supply.
- Oxidised IC sockets: degraded contacts cause random lock-ups; replacing the sockets often brings a “dead” board back to life.
- Stuck diagnostic LED: an LED that stays on continuously points to the U14 / U15 / U16 chips (often U15).
- Tired connectors: poor contacts between boards; redoing all of them is recommended.
Pinball-specific issues (forums)
Reported by enthusiasts on Pinside and repair forums:
- External ROM board: on Pinball and Stingray, which share the same ROM, the small add-on ROM board builds up cracked solder joints that need reflowing.
- Boot that locks up: the board stays stuck at power-up until the reset sequence is clean (a linear power supply is strongly recommended).
- SB-100 sound board / chimes: missing sounds or chimes, poor contacts and failed components on the period audio.
- Corrosion around U8: the classic battery-acid damage, with severed traces to rebuild.
- LED stuck on: diagnosis pointed at U15 (then U14 / U16) after checking the sockets.
Replacement boards compatible with Pinball
Rather than endlessly repairing 1977 electronics, replace them outright:
- BallyFA — MPU board (battery-free).
- BallyDri — power supply + driver.
- BallyLa_60 — lamp driver.
📚 Guide: which MPU board for a Bally / Stern (1977-1985)?
Plug & Play installation, battery-free, free support.
FAQ — Pinball (Stern)
Which board replaces the MPU of a Stern Pinball?
The BallyFA is a direct replacement MPU for Stern M-100 machines such as the Pinball: it installs in place of the original board, runs battery-free, and removes the corrosion risk from the start.
My Pinball stays dead or an LED stays on: can it be fixed?
Yes. A stuck LED usually points to the U14/U15/U16 chips (often U15). If the original board is too corroded, the BallyFA spares you an endless diagnosis.
Do I need a particular power supply?
The original M-100 reset circuit likes a linear supply. The BallyDri (power supply + driver) provides a clean foundation; if in doubt, contact us.
Can the original battery damage my machine?
Yes, it is the number-one fault on these boards. Our replacement boards run battery-free: no more acid leaks to fear.
How long does it take to install a replacement board?
Installation is Plug & Play: a few minutes, no soldering, with tutorials and free support.
Does a battery-free board keep the settings and high scores?
Yes. Modern replacement boards use non-volatile memory: no more battery, no more corrosion, and the settings are kept when powered off.
Step-by-step diagnosis
- Power off, visual inspection: look for any battery or corrosion traces on the MPU of your Pinball, especially around U10/U11; remove the battery if still present.
- Power supply: measure the 5 V and check it reaches the MPU; check the rectifier bridge and the power-supply fuses.
- Grounds: redo the grounds between the MPU, the power/driver board and the display.
- Connectors: repin the oxidised Molex connectors, especially the MPU↔power-supply link.
- Displays: never plug or unplug a display while powered on; test with a known-good display.
- Final test: check start-up, credits, coils and displays; the BallyFA replaces the MPU, battery-free. If needed, contact free support.
See also
Sources
- Pinside — “Pinball” (Stern) listing & forum: pinside.com/pinball/machine/pinball
- IPDB — Stern “Pinball” (#1792): ipdb.org/machine.cgi?id=1792
- Pinside — Tech “Stern MPU-100”, repair forums
