One or both flippers are weak, do not work, or buzz and stutter when held.

Flipper weak, dead, or machine-gunning

Cause: Dirty or misadjusted end-of-stroke switch, dirty cabinet buttons, a broken fine winding wire at the coil lug, a bad fuse or holder, a broken power feed, or a poor ground path through SDB J1 and the flipper relay.

Checks

• The EOS switch should be closed at rest and open about 3 mm (1/8") with the flipper fully up; always closed burns the coil, always open makes the flipper weak.
• Check both 1N4004 diodes and the coil wires at each lug; a broken thin (hold) wire causes machine-gunning.
• In game-over mode, measure about 43 V on all three flipper lugs (page 23). Only two lugs live: bad coil or EOS switch. None: fuses or the daisy-chained feed.
• Briefly ground the centre lug: if the flipper is now strong, the ground path back to the flipper relay is bad.
• Check the flipper relay pulls in at game start or in solenoid test, and look at its contacts.

Fix

• File the EOS and cabinet switch contacts clean and readjust.
• Replace a tarnished or loose fuse holder.
• On the solenoid driver board, repair burned traces between J1 and the relay and reflow the relay and J1 header joints.

Systems

• Bally MPU AS-2518-17
• Bally MPU AS-2518-35

Related tips

• Flippers weak or intermittent from the solenoid driver board
• Flippers dead though fuses and EOS switches are good
• Flippers stop working after a few minutes of play
• Flippers and some coils work, others are dead
• No coils work at all
• One coil dead with a good transistor and power at the coil
• Game resets or locks up when the flippers are used
• One flipper dead with fuses good

Source: Repairing Bally Electronic Pinball Games from 1977 to 1985, Part Three, Clay Harrell (pinrepair.com)