Flipper coil is overheating, weak flipper, fuse intermittently blows, flipper coil burns.

A defective flipper opto switch can cause this problem. The coil will overheat after while of playing and can burn. The flipper fuse can intermittently blow. The players usually complain that the flipper becomes weak after while of playing.

Check the opto switch with your multimeter. Measure directly on the flipper button opto board connector pin marked SW1 & SW2 against ground. You should measure below 0.7 volts (below 1V is still fine) with the button pressed. Higher reading means a dirty or defective opto switch. If cleaning does not remedy the problem (blow off the dust and use clean paint brush, don't use any cleaning sprays) replace the opto switch. Later models of Williams/Bally pinballs use Schmitt Trigger opto switch ( 3 legs on the receiver side) which eliminates this problem.

Replace the coil if it looks that has been severely overheated.