Hot Hand (Stern, 1979): faults and replacement board (Stern M-100 MPU)
Is your Hot Hand by Stern freezing part-way through the test routine, does it have a flipper that no longer fires, does it no longer fire any coil apart from the flippers, or is it left with dark displays? These symptoms are typical of Stern microprocessor machines (M-100 MPU): the original board is now more than 45 years old and has almost always suffered from a leaking battery. A battery-free replacement board gives the machine a second life.
Hot Hand (Stern, 1979): an introduction
Released in May 1979, Hot Hand is a solid state pinball machine from Stern Electronics designed by Harry Williams, on a cards and gambling theme. Its distinctive feature: a large motorised rotating flipper at the top of the playfield, which sweeps ten rollover pockets and keeps scoring for as long as the ball is not dislodged. Multipliers are earned with poker hands: pair 2X, three of a kind 3X, four of a kind 4X, all twenty cards 5X. It uses the Stern M-100 MPU board.
- Manufacturer: Stern Electronics
- Year: 1979
- Electronic system: Stern M-100 MPU
- Type: solid state pinball machine
- Theme: cards / poker
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 boot at all), oxidised or burnt Molex connectors between the MPU and the power supply, displays with missing segments, and a power supply and driver board that needs going over (bridge rectifier, fuses, coil transistors).
Problems specific to the Hot Hand (from the forums)
- The rotating flipper starts up on the 4th flash of the diagnostic and freezes the test: a classic fault, often cleared by unplugging the rotating flipper's motor connector, or the connector at the bottom right of the solenoid board.
- The rotating flipper's motor disturbing start-up: to be isolated before any diagnosis of the MPU.
- A left or right flipper that refuses to fire: the end-of-stroke (EOS) switch not closing in the down position, so the coil buzzes without actuating.
- A flipper that fires and then immediately drops back, with the machine returning to general illumination alone.
- Only the flippers working: no other coil responds, so the driver and power supply boards need checking.
- Doubtful connections on J1 and J2 in the backbox: re-pinning all of the backbox connectors makes the machine reliable for the long term.
Replacement boards compatible with the Hot Hand
Important: the Hot Hand uses a Stern M-100 MPU, close to but distinct from the Bally boards. Confirm the right board before ordering: get in touch with the part numbers of your boards.
- BallyFA — battery-free MPU.
- BallyDri — power supply + driver.
- BallyLa_60 — lamp driver.
Plug & Play installation, battery-free, free support.
FAQ — Hot Hand Stern
Which replacement board for my Hot Hand?
The Hot Hand is fitted with a Stern M-100 MPU: get in touch with the part numbers of your boards and we will confirm the right solution (battery-free).
My test routine stops when the rotating flipper starts turning.
Unplug the rotating flipper's motor connector, or the one at the bottom right of the solenoid board, then run the diagnostic again to isolate the fault.
A flipper buzzes but does not fire.
The end-of-stroke (EOS) switch is not closing in the down position: clean and adjust the contact before changing the coil.
Should I keep the original battery?
No: a battery-free board removes the number one cause of corrosion.
Does a battery-free board keep the settings and high scores?
Yes: non-volatile memory keeps the settings and scores when the machine is switched off, with no battery and no corrosion.
What warranty comes with boards from Pinballs Store?
A 6-month warranty (parts and labour) against any fault not caused by misuse, plus 30 days money back. Technical support is free.
Useful guides
- How much does pinball machine repair cost? The price guide
- How much is my pinball machine worth? Values and estimates
- Pinball machine leg sizes: the guide by machine
- Which MPU board for a Bally/Stern?
See also
Sources
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