Neither flipper works in a game or in diagnostics, and K1 on the CPU board does not click.

No flippers at all: flipper relay K1 not pulling in

Cause: Transistor Q67 (2N4401) most often; otherwise the 7402 at U50, the 7406 at U56, PIA U10, or the relay itself.

Checks

• Test Q67 first.
• With the CPU board out, put a 9 V battery across the relay's two coil lugs (the two set apart from the other 12): it should click firmly.
• Check U50, U56 and U10 with a logic probe.

Fix

• Replace Q67, the failed chip, or the relay (4PDT, 40 ohm coil, 6 V; Magnecraft W78CSX-1 fits).

Systems

• Williams System 11
• Williams System 11A
• Williams System 11B
• Williams System 11C

Related tips

• Flipper relay does not click on in test
• Flippers dead, or still live after game over: the flipper relay
• CPU and driver board transistors by position
• Game will not boot consistently: power-on reset (POR) circuit
• Quick check of all TIP122/102 drivers before first power-on
• CPU flipper enable relay RY1
• Flippers never work: flipper relay RY1 not pulling in
• Flipper enable relay K1 on the CPU board

Source: Repairing Williams System 11 Pinball 1986 to 1990, Part Two, Clay Harrell (pinrepair.com)