One of the three playfield magnets does nothing, or stays on for no reason.

Guns N' Roses magnets dead or locking on

Cause: Cracked solder joints on the FETs of the under-playfield magnet board (they hang upside down on large heat sinks), or electrical noise picked up by the long data wires from the CPU board.

Checks

• Inspect and reflow the FET joints first.
• If magnets still lock on randomly, suspect noise on the CPU data lines to the board.

Fix

• Reflow the FET solder joints.
• For noise, move the board into the backbox so the data wires are short (lengthen the magnet wires instead), or add 0.1 uF capacitors from the board's pull-up resistors to ground, which suppresses but may not cure it.

Systems

• Data East/Sega CPU Version 3b

Games

• Guns N' Roses

Related tips

• Last Action Hero / Guns N' Roses: magnet dead or locked on
• Guns N' Roses: magnets blow their 2.5 A fuse in multiball
• Guns N' Roses with a shaker motor was probably built for Japan
• Guns N' Roses: CPU and display EPROM types and latest versions
• Wide body glass size
• Magnet driver MOSFETs on Last Action Hero and Guns N' Roses
• From Guns N' Roses the cabinet is pitched with levelers fully in
• Removing the backbox door on Guns N' Roses and later

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