The game stops at a message saying the control board has a low battery or a bad U3 or U6.

"Control board error, Low battery or Bad U3 or U6"

Cause: Nearly always the flat 3 V lithium cell on the CPU board has run down.

Checks

• Measure the cell, but remember a cell reading 3 V can still be too weak (see the DS1210 note).

Fix

• Replace the CR2430, preferably with a socket.

Systems

• Gottlieb System 3

Related tips

• CPU battery and socket parts
• Fitting a CR2430 socket on the CPU board
• Getting past the low battery message
• Battery error stays after a new battery
• Using a remote two-AA battery pack
• Lithium battery leak damaging the CPU board
• Constant beeping, display blank, GI on
• Game stuck showing the last four high scores

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