I recently purchased an HPA-1 that was a dealer demo. When it arrived it would not power up. I went through the obvious stuff. Power source, power cable, it has an accessible fuse holder on the rear panel. All good. I found a forum thread that said this model has experienced issues with a ribbon connector. I copied it here:
“Thanks Thorensman, appreciate the suggestions. I got in touch with Pass Labs and they suggested that sometimes in transport the ribbon connecting the circuit board to the main panel comes undone. Sure enough when I opened it up, the ribbon had come loose. 3 mins later and all good! Glad it was an easy fix.”
Mine had basically the same issue. The connector wasn’t visibly disconnected, but I did reseat it and solved the problem. I realize your circumstances and gear are different, however it is something you could look at while you wait to get in touch with support. Good luck.