Peavey F-800b failure

After about 10 years of reliability my F-800B bass head crapped out the other day. I switch it on and all I got was a big buzz noise uneffected by the volume knob. I swapped cabs, cables and outlets around the room nothing worked.

I opened it up and traced the preamp board with a tone gen and audio probe got signal all the way thru. checked the power to the preamp board and didn't get a dc voltage so I switch to ac and got 53v ac. It's supposed to be 24v dc going to the preamp pcb.

checked the voltage on the big caps next to the power transformer and got 115v ac instead of 50v dc.

un-plugged the power trans and caps from the power amp pcb and wall. Tested the caps resistance and they climb to infinity like they should right?

The amp has been sitting it the same spot for weeks now and I've used it pretty much every week til now. Not sure how just sitting there it could fail this bad.

I'm thinking its the power transformer because of the incorrect voltages coming out of it but maybe I'm not reading the schem right. Attached is the schematic.....I think

not sure about that 115 ac reading, seems it would blow the fuse or blow up the caps as they have a very low resistance to 60/120 (120 is ripple freq) Hz AC which means they would suck a lot of current,  maybe that is ripple voltage you see, which means the caps have gone south, probably could use a cap job if you play bass,

rectifier bridge is probably pretty hefty, so it is probably ok,

try removing and replacing all the connectors, do you live in the pacific northwest? we had a wet year last year,  store the amp in the garage?

start at the beginning, disconnect the leads feeding the rectifiers, Peavey usually makes this easy with those molex type connectors,  wish i knew where to buy those, they are the most trouble free  connectors i have seen in an amp and they are easy to unplug,  i bet JR knows who the vendor is,

measure the transformer AC voltage from CT to the ends and see what you get,

CJ said:

not sure about that 115 ac reading, seems it would blow the fuse or blow up the caps as they have a very low resistance to 60/120 (120 is ripple freq) Hz AC which means they would suck a lot of current,  maybe that is ripple voltage you see, which means the caps have gone south, probably could use a cap job if you play bass,

rectifier bridge is probably pretty hefty, so it is probably ok,

try removing and replacing all the connectors, do you live in the pacific northwest? we had a wet year last year,  store the amp in the garage?

start at the beginning, disconnect the leads feeding the rectifiers, Peavey usually makes this easy with those molex type connectors,  wish i knew where to buy those, they are the most trouble free  connectors i have seen in an amp and they are easy to unplug,  i bet JR knows who the vendor is,

measure the transformer AC voltage from CT to the ends and see what you get,

Click to expand...

I went thru and sprayed conduct cleaner in all the connectors when I first started testing it.

I unplugged the transformer for the power amp board and measured the ac coming off the two leads coming out of it and got 36v  on each.

i plugged them back in but left enough space to sneak a prob in and got the same of the main leads(which are the center pin on the connector) and the top pins had 115 , bottom nothing.

see pic