The kickback fires reliably for players 1 and 3 but never for players 2 and 4. The kickback coil works in solenoid test.

Kickback only works for players 1 and 3: update the game ROMs

Cause: A software bug in early or prototype game ROMs. Members noted an early prototype version (PA-6) showing this, and a later release (L4) that did not.

Checks

• Open the coin door and enter test to see the game ROM version shown at start.
• Try a factory reset first to rule out a bad setting.

Fix

• Install an up-to-date set of game ROMs.

Systems

• Williams System 11B

Games

• Black Knight 2000

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