Hissing and popping generally would point to a PSU problem, specifically:
a capacitor
1 or more diodes
a device on a heat sink
In that order.
I don't see anything to indicate a bad cap. I can't see the devices on the heat sinks, so one of them might contain some charcoal.
Start with checking the fuse.
Then eyeball and smell the board.
Then test the diodes with the diode function on a DVM.
Replace parts as necessary.
I'm betting the fuse and a diode or two.