A rollover lamp on the auxiliary lamp driver board stays lit. Replacing the SCR the schematic points to (and its driver chip) doesn't help.

Rollover lamp stuck on after a new SCR: schematic labels swapped

Cause: The schematic has the top left and top right rollover lamps the wrong way round, so the wrong SCR was being replaced. The SCR actually driving the stuck lamp (Q6) had failed.

Checks

• Unplug the lamp board connector to confirm the lamp goes out (rules out a wiring short).
• Check the wire colours at the lamp against the board connector rather than trusting the lamp names on the schematic.

Fix

• Replace the SCR that really drives the stuck lamp.

Systems

• Bally MPU AS-2518-35

Games

• Centaur

Related tips

• No GI at all: failed Q14 SCR on the main lamp driver board
• Lamp driver, auxiliary lamp driver and display driver test points
• Auxiliary lamp driver boards: SCR to connector pin
• Substitute SCRs for the lamp driver board
• Lamp driver board layout: SCRs, decoders and connectors
• Lamp driver board: which SCR drives which connector pin
• Bottom spinner insert always lit: it is a GI lamp, not a stuck one
• Auxiliary lamp boards drive special backbox lighting with MCR106 SCRs only

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