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.