Hi everyone! First time here, glad I found this site.

I have a problem with my iMac which suddenly shutdown during a macos update. It turns on to a black screen, the fan is running, off-sequence LED (1-off, 2-3on, 4-5off). Tried replacing the PSU with known working PSU but that didn't fix it. Tried to swap RAM but that didn't fix. I'm now trying to find schematics for my board (820-01310-A is the number printed on it) to better understand the power rails. It seems like it's an unusual configuration, I have the i9 3.6ghz with Vega 48.

Also, someone told me it could be...