I just shopped out my BK2K the other day. Found it strange that a few flashers that should have 906 lamps in them only had 555 lamps. I swapped everything out to new, proper flash lamps.

Now, almost none of my flashers work. 2 of them worked earlier today & even more worked before the shop job, now only 1 flash lamp on the whole game seems to work.
So obviously the relay works. All fuses definitely good, all header pins good & re-soldered, all boards inspected, the interconnect board with all the resisters seems to check out OK.
All transistors seem to test OK as well. Lower interconnect board seems good. Board wiring seems good from what I can tell.

I can't think of what else I can do to find the problem. All my coils fire OK, game otherwise functions OK, though I think I have a bad lamp diode to track down since I have some double lamp lighting in test mode but I assume that is unrelated.
The fact that the game had a number of 555's for flashers instead of 906's is now starting to concern me. Was the use of 555's somehow bypassing an issue that was never dealt with?