Is your tilt trip relay tripped? It's in the middle of the trip bank on the back door.

If it is, what happens if latch it (with power off) and try again? Does it trip immediately?

If it is not, then your issue is likely in your 50V circuit, which of course runs through everything. My prime suspect is usually control unit cam switch 3A. A lot of current runs through that switch and it is normally pitted enough that the slightest disruption kills 50V through the majority of the game - especially the startup circuitry.

Great that you got it going! Sometimes it just takes a clear mind and some time to solve a problem.

Thanks for reporting the resolution!