Trident (Stern, 1979): faults and replacement board (Stern M-100 MPU)
Is your Stern Trident refusing to boot, stuck on a locked-up start-up, showing drop targets that won't reset or dead displays? These symptoms are typical of Stern microprocessor machines (M-100 MPU): the original board is over 45 years old and almost always suffers from a leaking battery. A battery-free replacement board gives the machine a second life.
Trident (Stern, 1979): overview
Released in March 1979, Trident is a solid state pinball machine from Stern Electronics designed by Mike Kubin, with roughly 4,019 units produced. The playfield is deliberately clean: two flippers, two bumpers, a bank of five drop targets and rollunder spinners. No multiball, no ramp, no speech. It uses the Stern M-100 MPU board.
- Manufacturer: Stern Electronics
- Year: 1979
- Electronics: Stern M-100 MPU
- Type: solid state pinball machine
- Theme: sea mythology / Neptune
Common faults (Stern M-100)
On Stern M-100 machines (1977-1979), the recurring faults come down to age: a leaking battery on the MPU (corroded traces around U10/U11, the number one cause of dead boards), tired logic chips (5101 RAM, 6821 PIA, no start-up at all), Molex connectors oxidised or burnt between MPU and power supply, displays with missing segments, and a power/driver board in need of attention (bridge rectifier, fuses, coil transistors).
Problems specific to Trident (from the forums)
- M-100 MPU that refuses to boot: this is the most discussed issue on Trident machines, with the diagnostic LED stuck on solid.
- Corroded socket at U11 (6821 PIA): as long as a pin isn't making contact, the game won't start; clean the legs or replace the chip.
- Bank of five drop targets that no longer resets: seized mechanism, reset coil or driver transistor to check.
- Rollunder spinners that stop counting: dirty or misadjusted switch contacts, to clean and reset.
- Flipper that buzzes without firing: the end-of-stroke (EOS) switch isn't closing in the down position.
- Leaking battery on the MPU: deal with this before any other diagnosis.
Replacement boards compatible with Trident
Important: Trident uses a Stern M-100 MPU, close to but distinct from the Bally boards. Confirm the right board before ordering: contact us with the part numbers on your boards.
- BallyFA — battery-free MPU.
- BallyDri — power supply + driver.
- BallyLa_60 — lamp driver.
Plug & Play installation, no battery, free support.
FAQ — Trident Stern
Which replacement board do I need for my Trident?
Trident is fitted with a Stern M-100 MPU: contact us with the part numbers on your boards and we'll confirm the right battery-free solution.
My Trident won't boot at all.
Start with the battery and the corrosion around U10/U11, then check the 5 V supply and the U11 socket before concluding the board is dead.
My bank of five drop targets stays down.
Check that the mechanism moves freely, then the reset coil, then the corresponding driver transistor.
Should I keep the original battery?
No: a battery-free board removes the number one cause of corrosion.
Does a battery-free board keep settings and high scores?
Yes: non-volatile memory keeps settings and scores when the machine is switched off, with no battery and no corrosion.
What is the warranty?
6-month warranty (parts and labour) against any fault not caused by misuse, plus 30 days money back. Free technical support.
Useful guides
- Which replacement MPU board for a Bally or Stern?
- Repair or replace a pinball circuit board?
- How to buy a pinball machine without breaking the bank
See also
Sources
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