Start Motor on a Pinball Machine Keeps Running

Start Motor on a Pinball Machine Keeps Running

Blog Article

Pinball Start Motor Functionality

1. 
   
   Role in Game Operation
   
   
   
   
   • Electro-Mechanical Machines (1960s–1970s):
     
     
     
     • The start motor (often a small DC gearmotor) resets score reels, kickers, and flipper linkages when the game is started or reset.
     
     
     
     
   
   
   • Solid-State Machines (1980s–1990s):
     
     
     
     • Replaced by solenoids and stepper motors, but some models still use a start motor for complex mechanical resets.
     
     
     
     
   
   
   
   


2. 
   
   Normal Operation
   
   
   
   
   • Activated by the start button or coin mechanism, running for 1–3 seconds to complete reset sequences.
   
   
   • Deactivated by a microswitch or cam-operated switch once reset is complete.
   
   
   
   

Causes of a Continuously Running Start Motor

1. 
   
   Stuck Mechanical Switch
   
   
   
   
   • Cam-Operated Switch Failure:
     
     
     
     • In EM machines, a cam on the motor shaft triggers a switch to stop the motor. If the cam is misaligned or the switch arm is bent, the switch remains closed, keeping the motor running.
     
     
     
     
   
   
   • Example:
     
     
     
     • The reset cam in a Gottlieb System 1 machine fails to push the switch open, creating a continuous circuit.
     
     
     
     
   
   
   
   


2. 
   
   Wiring Short or Solder Bridge
   
   
   
   
   • Electrical Fault:
     
     
     
     • A short between the motor power wire and ground, or a solder bridge on the control board, bypasses the switch and keeps the motor energized.
     
     
     
     
   
   
   • Common Culprit:
     
     
     
     • Corroded or frayed wires near the motor or under the playfield.
     
     
     
     
   
   
   
   


3. 
   
   Defective Relay or Transistor
   
   
   
   
   • Solid-State Machines:
     
     
     
     • A stuck relay (e.g., in a Williams System 3) or failed power transistor keeps the motor circuit closed.
     
     
     
     
   
   
   • Testing Clue:
     
     
     
     • The motor runs even when the start button is not pressed, indicating a faulty control component.
     
     
     
     
   
   
   
   

Diagnostic Steps for EM Pinball Machines

1. 
   
   Visual Inspection
   
   
   
   
   • Check the start motor’s cam and switch mechanism:
     
     
     
     • Ensure the cam rotates freely and pushes the switch arm to the "open" position.
     
     
     • Look for bent switch arms, broken springs, or debris jamming the mechanism.
     
     
     
     
   
   
   
   


2. 
   
   Switch Continuity Test
   
   
   
   
   • Use a multimeter to test the reset switch:
     
     
     
     • Should be open when the motor is at rest, closed only during the reset cycle.
     
     
     
     
   
   
   • Fault Indicator:
     
     
     
     • If the switch remains closed indefinitely, adjust or replace it (e.g., Gottlieb part #805-5555-00).
     
     
     
     
   
   
   
   


3. 
   
   Wiring and Component Check
   
   
   
   
   • Trace the motor’s power wires (often red and black) for shorts to ground.
   
   
   • Inspect the score motor (if separate) for cross-wiring that could activate the start motor accidentally.
   
   
   
   

Troubleshooting Solid-State Machines

1. 
   
   Relay Testing
   
   
   
   
   • Locate the start motor relay (e.g., on the driver board of a Bally/Stern machine):
     
     
     
     • Listen for buzzing or feel for warmth; a stuck relay will remain energized.
     
     
     • Swap with a known good relay (e.g., G6B-1114P-FD-US) for testing.
     
     
     
     
   
   
   
   


2. 
   
   Transistor and Diode Checks
   
   
   
   
   • Test the power transistor (e.g., TIP122) driving the motor:
     
     
     
     • A shorted transistor will keep the motor on; replace with a heat sink and thermal compound.
     
     
     
     
   
   
   • Check for a blown diode (1N4004) across the motor terminals, which can cause runaway operation.
   
   
   
   

Safety and Damage Prevention

• Immediate Action:
  
  
  
  • Unplug the machine or disconnect the battery (if equipped) to stop the motor and prevent overheating.
  
  
  
  


• Overheat Risks:
  
  
  
  • A running start motor can reach 150°F (65°C) within minutes, melting plastic gears or warping metal components.
  
  
  
  


• Component Protection:
  
  
  
  • In EM machines, the start motor is often a 6V DC gearmotor (e.g., Mabuchi RS-385SH); continuous operation will wear brushes and reduce gear life.
  
  
  
  

Vintage Pinball Maintenance Tips

• Preventive Maintenance:
  
  
  
  • Lubricate motor gears with white lithium grease annually to reduce friction and prevent binding.
  
  
  
  


• Switch Adjustment:
  
  
  
  • Use a switch blade adjuster to set the reset switch gap to 0.015–0.020 inches (0.38–0.51 mm).
  
  
  
  


• Component Upgrades:
  
  
  
  • Replace mechanical switches with solid-state reed switches (e.g., N.O. reed switch #17-0045) for more reliable operation.
  
  
  
  

Common Models and Issues

• Gottlieb EM Machines (e.g., Haunted House):
  
  
  
  • Camshaft wear on the score motor can misalign the start motor reset switch.
  
  
  
  


• Williams Solid-State (e.g., Black Knight):
  
  
  
  • Faulty 5V regulator on the CPU board can cause erratic motor control.
  
  
  
  


• Bally/Stern (e.g., Star Trek: The Next Generation):
  
  
  
  • Corroded connectors on the driver board lead to stuck relays.
  
  
  
  

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