One circuit of playfield GI lamps is very dim. The board supplies the normal voltage (about 6.4 V AC) at its pins, but the bulbs see only about half that.

One string of GI lamps very dim: replace the bad GI wiring

Cause: Bad wiring in that GI string was dropping the voltage.

Checks

• With the lamps lit, measure the voltage drop across each connection point from the board to the dim sockets; the worst drop shows the bad spot.
• Check the GI connectors on the power and driver boards for burnt or loose pins and reflow the header pins.
• Remove the bulbs and refit them one at a time to rule out a shorting socket.

Fix

• Run new wire for the dim part of the GI string (and repin any burnt connector).

Systems

• Data East CPU Version 3

Games

• Teenage Mutant Ninja Turtles

Related tips

• Lamps on a plug-in lamp board do not light
• GI bulbs burning out quickly
• A group of clock lamps never light with good wiring: reseat the bulbs in their sockets
• Bulb spares: #44 for CPU lamps, #47 for general illumination
• A single lamp is out: the usual causes
• General illumination dead or dim
• One controlled lamp never lights, bulb is good

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