Peavey Studio Pro 50: Burned power supply

[JerkyPudding]

Hi all,
I have a Peavey Studio Pro 50 on the bench. It has a blown fuse, and upon further investigation, the zener diodes and 22uf/25v caps in the 15v power supply have burn marks around them. The large resistors in series with the diodes are showing heavy burning on the board as well. Which component would likely be the culprit in this? I'm still in the process of testing, but if this is something fairly common, I'd like to be pointed in the right direction. I appreciate the help.

Thanks!

[Enzo]

There is a difference between burnt and discolored. If you mean the large 400 ohm 5 watt R73, R74, it is normal for them to run hot and they will discolor the board over time. Do they still measure 400 ohms? In operation is there about 15v on one end of each resistor and about 36-40v on the other end of each? If so, all is normal there.

Usually when a solid state amp blows the fuse, there is a bad output transistor. Further down the list might be a shorted main rectifier. Other things are possible of course.

it also could just be a failed fuse.

If the unit blows fuses repeatedly, disconnect any load from the output and start looking.

Build a light bulb limiter and use it.

[JerkyPudding]

It's looking pretty burnt. There's scorching on the underside of board, particularly where the resistors are. I found a cold-solder on one of the diodes, so it must have been getting pretty hot. There is also a brown film covering the master vol. pot nearby, and some signs of high heat on the large filter caps. I'll get some pics shortly. The customer complained about intermittent cut-out and crackling noise, it got worse with time until the fuse popped. I'll take a look at the output section, let you know what I find.

Thanks for the input, I appreciate it.