The report
"Two cabinets in the bottom right are dark. The rest of the wall is fine. We restarted the processor twice." Two adjacent cabinets, same row. That pattern usually points to one receiving card feeding both, or one power supply feeding both.
First question: which cabinets
We asked for the cabinet numbers from the commissioning drawing. They were C13 and C14, which sit side by side and share a power feed from one 200 W supply. That ruled out the card, because C13 and C14 have separate receiving cards.
Second question: any light at all
The client sent a photo in a dark room. There was a very faint glow on two modules in C13, no glow at all in C14. That told us the supply was not dead but was dropping out under load, which is typical of a failing capacitor rather than a blown fuse.
Third question: what changed
Nothing, they said. Then: "the weather has been hot." The cabinet cavity was reading 54 degrees. A supply rated 200 W at 25 degrees derates to about 150 W at 55 degrees. The wall had been running at 70 percent brightness, which is close to that limit.
The fix
Replaced the 200 W supply with a 250 W unit, and added a vent to that cavity. Total parts cost about 40 dollars. The client had been quoted a full card replacement by a local contractor.
What we changed in the quote template
Outdoor-adjacent indoor walls now get a power budget with a 30 percent derating margin at the expected cavity temperature. It costs a few dollars per cabinet and removes this class of call.
The general lesson
Two dark cabinets in the same row are usually a shared power feed. Two dark cabinets in different rows are usually a card or a cable. The pattern of what is dark is the diagnosis, and it is free.