After changing several bulbs elsewhere, one insert lamp (here the R in CRANE by the drop targets) stays out even with known good bulbs and sockets.
One insert stays dark with good bulbs and sockets: failed diode on its lamp board
Cause: The diode for that lamp on its small lamp board had failed; the timing with the bulb work was a coincidence.
Checks
- Check whether only this lamp is out or a whole row or column of the lamp matrix.
- Find the lamp's diode on the lamp board and compare its meter reading in diode mode with the others.
- Wiggle the board's plug in lamp test to rule out a cracked joint.
Fix
- Replace the failed diode on the lamp board (a 1N4004-type diode can be used).
Systems
Games
Related tips
- Several lamps in one matrix row won't light: rusty sockets, diodes and joints
- Test a lamp socket diode in place
- One controlled lamp never lights, bulb is good
- Lamp socket diode orientation and 555 socket contacts
- A group of clock lamps never light with good wiring: reseat the bulbs in their sockets
- Lamps on a plug-in lamp board do not light
- Bulb spares: #44 for CPU lamps, #47 for general illumination
- A whole row or column of lamps is stuck on and extra bright
Source: Pinball Repair help group!! (Facebook group)