Peavey CS800S - no power

[misterc57]

My latest project is a CS800S that does not turn on. No lights, no fans, nothing turns on. I checked the circuit breaker fuse and the ON/OFF switch; they are both ok with a closed loop.

I have a hard to read schematic (poor quality). Right now I cannot figure out how to get to the power supply. See pictures. Seems like most of what I want to test is under that large PC board and I cannot figure out how to get there or pull that whole section out of the amp.

Much thanks for the help to come!

[The Dude]

I haven't worked on one of these for quite a while, so I don't remember for sure the ins and outs of getting the supply out.
One thing I do remember though is that there were solder problems on at least one of the top PS boards. Some of the heavier components had their joints crack loose from the board due to them hanging off of it. You might check it over good before you go to the trouble of tearing the thing down.
Also, you said you checked the breaker and switch, but I would also check the power cord and, if you can find where the AC actually enters the supply, maybe you can verify that AC is actually there without major disassembly.
Just a couple of ideas that may save you some work.

[Jazz P Bass]

Just so you are aware, the unit uses a switch mode power supply.

[Enzo]

I forget now, but seems to me the whole SMPS assembly comes out. You'll have to find all the screws and may have to remove a couple things like the breaker maybe.

The SMPS is EXTREMELY dangerous to work on. It directly rectifies the mains. That means something like 340vDC with all the vurrent in the world just waiting to stop your heart. You want to use an isolation transformer. Also you cannot just bring it up on a variac. Peavey has a detailed service power up procedure, call customer service and ask for it.

A dead SMPS may be dead, but they are also usually swimming in protections, so a blown amp channel or a shorted rectifier on the secondary side will make it shut down.

[misterc57]

Finally got the PS out. I found fuse F2 is open. There are 4 diodes (bridge rectifier) CR103, CR104, CR105, CR106 connected to the fuse. I assume they need to be tested out of circuit. Any suggestions on what to look for with this blown fuse?

The fuse holder type does not allow for a push in and pull out of the fuse. Does this type need to be soldered out or can the ends be bent back to release the fuse? Never dealt with one of this type before.

Thank you!

[misterc57]

The F2 fuse is originally a 160ma. Peavey now recommends using a 250ma. The amp is now working after replacing the fuse.