SunkenCity
Well-known member
- Joined
- May 31, 2017
- Messages
- 58
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
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