The service buttons misbehave: the black button opens the portal menu and it scrolls through the options non-stop, and the red button opens the volume menu but won't change the volume. A new button assembly and a repaired, bench-tested CPU board made no difference.

Portal menu scrolls by itself and volume won't change: pinched wire at the coin door

Cause: A wire from the green button had been pinched (shorted) on the coin door assembly when a bill acceptor was being fitted.

Checks

• With the game on, unplug the CPU connector that carries the service buttons (CN6 here): if the scrolling stops, the fault is in the wiring or buttons, not the board.
• These are direct switches with no diodes, so continuity-test each button wire and look for insulation crushed against the coin door metal.

Fix

• Free and repair the pinched wire and re-route it so the coin door hardware can't crush it again.

Systems

• Sega/Stern Whitestar

Games

• The Lost World Jurassic Park

Related tips

• Whitestar: I/O board blanking LED flashes, lamp rows 1 and 3 dead: data bus short

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