I have one single playfield lamp not working. I replaced the 1n4004 diode at the lamp base, tested the circuit by bypassing the base altogether to rule out bad weld joint in the base itself. If I put a bulb from the input wire directly to ground it lights and stays on constantly. The partner lamp that shares the other phase of the driver transistor (Q28 in this instance) works just fine. I've ruled out the driver transistor, the lamp base, the 1N4004 (replaced with 1N4007), multiple incandescent bulbs, and nothing works.
Fyi, it is a Special Force machine, the Upper Left "FIRE" light isn't working. Per the manual it is on Q28 and shares that transistor with "Bomb 4". Again, aside from a few of the GI lights, this is the only active playfield light that doesn't work. What else could it be?