The game locks up at random (the display may blank and the sound sticks on a note) and sometimes ignores a drained ball until it is power cycled.
Random freezes and drained ball ignored: broken diode on a flipper coil
Cause: The diode on a recently replaced flipper coil had been poorly soldered and broke off, so the coil's switching spikes upset the CPU.
Checks
- Inspect the diodes on every coil, flippers first, and touch them gently; look for scorched wires at the lugs.
- Check the +5 V supply, and use the CPU's diagnostic display code (with the coin door open) to rule out a board fault.
- Reseat the backbox connectors and look for cracked header joints.
Fix
- Clean up the coil lugs and fit a new diode, soldered properly with the band on the power side.
Systems
Games
Related tips
- Testing flipper coil diodes
- Every System 11 flipper has an EOS switch and coil diodes
- Flippers and lock kickout dead with good fuses
- Flipper coils have two windings
- How the two windings of a flipper coil work
- How a System 11 flipper coil works
- Measuring a flipper coil's windings
- Removing and checking the flipper coil stop
Source: Pinball Repair help group!! (Facebook group)