This PCB is from my Kawai K3 synthesizer. 5 transformer leads come in. 8VAC across 2 orange leads, 20-0-20 across red, black, red or 40VAC red to red.
I picked the synth up dead. I immediately found a dead rectifier. I changed the rectifier and the two fuses let go.
There must be something downstream that pulls too much current, a short of some type.
Coincidence: I had something like that on a Yamaha something, and it was a bad tantalum cap that would systematically kill the 5V rail. Not easy to detect, if I remember correctly, I traced the rail out of the regulator, looking for causes.
You're not saying anything about regulators: check those first next thing.
When I first glanced at it. It had a peculiar appearance to it but as it turns out it is fairly straight forward in design. I ran out of fuses while testing it but I swapped in new 7815 and 7915 and all new caps for the 15 Volt section. Still losing fuses in the 15 V section so I think the 5V is shorting it. Think I will spend some time today.