A coil or flash lamp energises solidly at power-on.

Coil or flasher on as soon as the game powers up

Cause: Its driver MosFET has shorted and holds the ground side on. A coil that never fires (with power present) usually has an open MosFET.

Checks

• Find the MosFET in the schematic.
• Test it with the meter's diode range.

Fix

• Power off quickly to save the coil; replace the MosFET with a logic-level part.

Systems

• Gottlieb System 3

Related tips

• Cue Ball Wizard: coils holding on weakly (BUZ72L MosFETs)
• Coil MosFET ratings and substitutes
• Lamp and switch matrix size and drivers
• Lighting a whole lamp column by hand
• Spare MosFETs for the driver boards
• Logic chips worth stocking
• What the A3 driver board drives
• Bottom cabinet relays and their drivers

Source: Repairing Gottlieb System 3 Electronic Pinball Games from 1989 to 1996, Clay Harrell (pinrepair.com)