Basic single-LED replacement bulbs will not light in some of the controlled lamp sockets under the playfield, while brighter multi-chip LEDs or incandescent bulbs work there, and every type works in the GI.

Gottlieb System 3: cheap LEDs stay dark in some insert sockets: polarity

Cause: Simple LED bulbs without a built-in bridge rectifier only light one way round, and some lamp sockets on these lamp boards are wired with the opposite polarity to the rest.

Checks

• Swap an incandescent bulb into a dark socket: if it lights, the socket and driver are fine and the LED is polarity sensitive.

Fix

• Use LED bulbs with a built-in bridge rectifier (non-polarized), or reverse the affected sockets' polarity.

Systems

• Gottlieb System 3

Related tips

• Which bulbs System 3 games take

Source: Pinball Repair help group!! (Facebook group)