Every device in one bank (the L/A coils or the R/B flashers) fails to work.

All L or all R bank coils/flashers dead: PPB relay K1

Cause: The PPB L/R select relay K1, driven by CPU TIP122 Q29, very often has cracked solder joints; its contacts can also burn or weld.

Checks

• Inspect all eight K1 solder points (two for the coil, six for the two DPDT contact sets).
• Check that Q29 switches the relay coil.

Fix

• Reflow the relay joints.
• Replace a relay with burnt contacts with the same 24 V DC 10 A double-DPDT type.

Systems

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

Related tips

• Only flash lamps work when a game starts (L/R reversed games)
• Balls keep launching as soon as a game starts
• Random coils firing and dead flashers on Tales from the Crypt
• L/R relay burnt or intermittent
• Several bank-switched coils or flashers dead, or firing the wrong device
• Under-playfield relay boards and the PPB board
• Bank select relay and CPU transistor Q29
• Use the manual's coil/flasher chart to find driver transistors

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