The flippers never come on, in a game or in test. The flipper relay barely pulses, and pushing it in by hand makes the flippers work until the game ends.

Flippers dead, flipper relay only buzzes faintly: replace the relay's diode D1

Cause: The diode D1 across the flipper relay coil was faulty even though it tested good on a meter out of circuit. The relay, its driver transistor and the gate chip had already been replaced without curing it.

Checks

• Confirm the relay is the correct 6 V flipper relay.
• With the game on, briefly ground the non-banded end of the relay's diode with a clip lead; a good relay pulls in firmly.
• If the relay pulls in that way but not under game control, check D1, then the gate chip and the small driver transistor that switch the relay.

Fix

• Replace D1 (and reflow its joints) and retest the flippers.

Systems

• Williams System 4

Games

• Phoenix

Related tips

• Flippers dead, or still live after game over: the flipper relay
• Flipper relay does not click on in test
• Power at the flipper coil but no flip
• A whole lamp row or column dead or stuck on
• Whole game dead after working on a flipper EOS switch
• The usual causes of a dead System 3 to 7 board set
• Diode-test the TIP120/TIP102 and 2N4401
• Never leave a locked-up game switched on

Source: Pinball Repair help group!! (Facebook group)