After swapping the CPU battery for a coin cell in a remote holder, the game shows a low battery / bad U3 or U6 control board error. After a factory reset it boots from cold, but a quick off-and-on gives a continuous beep and it won't start again for hours.

Low battery / Bad U3 or U6 error and beep loop after a coin cell swap

Cause: The first error is normal after the battery is removed with the game off; the settings are lost. The beep loop on warm restarts went away once the battery holder was on the board itself and two capacitors near it were replaced.

Checks

• Do a factory reset after any battery change made with the game off.
• If a remote holder on long wires was added, suspect it first.

Fix

• Remove the remote holder and wiring and fit a coin cell holder directly on the CPU board.
• Replace capacitors C20 and C21.

Unplug the game and take the CPU board out before soldering. Check the board around the old battery for corrosion.

Systems

• Gottlieb System 3

Games

• Wipe Out

Related tips

• Low battery error comes back a month after a new coin cell: the new cell was bad
• Garbled replay score setting after a battery change: repeat the factory reset
• Gottlieb System 3 CPU passes test ROM, then watchdog trips: torn trace and wrong parts
• Suddenly won't boot, CPU and DMD LEDs solid, display dark: reseat playfield ground plugs
• Where the boards sit in a System 3 dot matrix backbox
• "Control board error, Low battery or Bad U3 or U6"
• Judging battery corrosion damage
• Battery error stays after a new battery

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