I've got two 400 SMT's that were both claimed to be DOA, and found that I was able to get one going by swapping the main driver board and interface PCB out with one from the other machine. By scoping the outputs to the SCR assemblies with the bad board I'm barely getting a tenth of a volt and an extremely noisy waveform, whereas the other driver board outputs a strong and stable PWM waveform around 5 VDC.

Arcon says they don't have a preferred company to rebuild this board, and a new OEM one is over $700 so finding a cheaper repair option would definitely be preferable, unless someone on here has some extra working boards or a machine they're parting out with a good main board.