As soon as the game is switched on, one coil or flash lamp energizes and stays energized (it may get hot and smoke).

A coil or flasher comes on and stays on at power-up

Cause: Most often its driver transistor has shorted. Less often the 2N4401 pre-driver, the 7408/7402 gate feeding it, or the 6821 PIA behind that has failed.

Checks

• Switch off at once. Find the coil in the manual coil table to learn which transistors drive it.
• Measure the coil with a meter on ohms; anything under 3 ohms is shorted and must be replaced before new transistors go in.
• Diode-test the driver and pre-driver transistors with the board out (see the transistor test entries).

Fix

• Replace the driver and its pre-driver together; for a TIP36c, also replace the TIP122/TIP102 and 2N4401 that drive it.
• Replace the diode on the coil if it is broken or doubtful.
• If the device still locks on, replace the 7402/7408 gate, then the 6821 PIA.

Systems

• Data East CPU Version 1/2
• Data East CPU Version 3
• Data East/Sega CPU Version 3b

Related tips

• Flash lamp stuck on and melting plastics on L/R reversed games
• How a coil or flasher is switched: PIA to TTL to pre-driver to driver
• Lamp column still dead after a new TIP42
• Quick test for shorted TIP122/TIP102 drivers
• Which logic chips drive which solenoid transistor pairs
• One or a few coils lock on at power-up
• Damage after the black and white plugs were swapped
• Quick check of all TIP122/102 drivers before first power-on

Source: Repairing DataEast 1987 (Laser War) to Sega 1995 (Batman Forever), Part Two, Clay Harrell (pinrepair.com)