Hypex N400 problem

I have tried searching old posts for my issue and have not found it. apologies if i missed it.

i have 2 n400 monoblocks in ghent cases i purchased on us audio mart in early 2018. someone else assembled them but the works seems to be competent. the power supplies are smps 600 version 3.

a few weeks ago i started having trouble with one of the amps. the sound would stop and start. then it stopped altogether. i pulled them out and finally popped the top yesterday. no apparent issue, but both the 400 board and the power supply are very complex.

running the bad one again this AM. same issue: will play for 3 or 4 seconds, stop for a second or 2 and start again. all the lights on the 400 board appear to be lit up. wiggling wires (none appear to be loose) makes no difference.

i tried a different power cord; different cable--no difference. i also tried my TPA3250 amp in the same rig with same power cord and cables and it worked fine.

if it is the power supply i can just order a new one. can someone give me troubleshooting tips?

many thanks!

EDIT: now after running for about 45 minutes or so the amp is playing continuously. will keep minitoring. still seems like something i need to figure out.
EDIT2: now no sound at all. when i turned off and then on the amp won't light up; dead. definitely points towards power supply. heat sink is pretty warm (running with the top off).
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