Here is an excerpt from the old Pinrepair guides which is a good place to start......

Note I have seen a problem with a Fliptronics board where the flipper "fluttered".
Normally this would be a hold flipper coil problem, or a Fliptronics TIP102 problem.
But in this case it was the Fliptronics TIP102's 1N4004 diode that has failed, which
caused the flipper flipper (or "double flip") and not hold in the up position. I found
this problem because the 2.6k ohm 1 watt resistor tested low (1.8k ohms). After
removing one end of the resistor from the board, I found the resistor tested
correctly (2.6k ohms). I then tested the 1N4004 diode again and found it read 1.2
volts (not .4 to .6). Replacing the diode fixed the flipper flutter problem. Note I had
previously replaced the TIP102/2N4403 transistors (and not the 1N4004 diode!) and
the flipper still fluttered.