First of all, did you check the fuse?
If there was some info (schematics) about this unit I would be glad to give you a hand... but Andrew is very secritive with his schematics (and who can blame him, having in mind how much his products have been ripped off). So I'd recommend contacting Tech21 directly for any diagnostic and repairs. It anyways sounds like a power supply problem (I did't get if the pilot light turns on?) if it doesn't, is for sure a power supply issue... which are the easiest to repair.
Hope you find a solution soon.
But if the light does turn on, it could be a problem with the input/output buffer, or the bypass matrix (I am guessing the rack units use Flipflops and Jfets like the pedals) in that case the debugging is a bit more complicated... but again, is their machine, I bet they know how to fix it

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Best Regards!
Doug.