UcD400 No Output

I am helping a friend troubleshoot his custom UcD400 based amp which lost one channel of output and now both. I don’t have any experience with these modules short of testing input power and signal, output signal, etc. Fuses look okay and I’m measuring 64vdc out from the power supply, so anything specific I should know about the boards? Maybe they have a trigger that’s gone bad or something?

Thanks for the help!