None of the CPU-controlled lamps light, while the rest of the game works.

All controlled lamps out: bad spade connections on the bridge rectifier

Cause: Poor connections at the push-on spade terminals of the bridge rectifier feeding the lamp supply. A diode test of the rectifier while it is still wired in can also give a false 'bad' reading because the transformer winding is in the circuit.

Checks

• Check for the lamp supply voltage at the rectifier output.
• Inspect the spade connectors on the rectifiers for looseness, heat discoloration or corrosion.
• Before condemning a rectifier, disconnect its wires and diode-test it out of circuit.

Fix

• Clean or replace the spade connectors, or cut them off and solder the wires directly to the rectifier lugs; replace the rectifier only if it fails out of circuit.

Unplug the game before working near the transformer and rectifiers.

Systems

• Williams System 6 / 6A

Games

• Firepower

Related tips

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• A whole lamp row or column dead or stuck on
• Flippers too weak for the top lock: loose, arcing bridge rectifier connections

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