Hi everybody - I need some help getting my old Fender M80 combo back in shape.
The main problem is this: I get intermittent output from the amp when powering up, but I'm not sure where the problem lies.
For example, I can power up the amp and everything is on and the channel select light works, but I don't hear that little 'thump' from the speaker, telling me it's receiving power. There is just no sound coming from the speaker.
Then if I plug into either of the input jacks and toggle the power switch on and off for a while, I may get lucky and hear the little 'thump' and all works fine. The speaker powers and I can use the amp as intended.
That little 'thump' of the speaker getting power I'm talking about should happen regardless of whether I'm plugged in to the inputs or not, but I can only seem to resolve it by using the toggle method above.
The odd thing is, when it's working the amp is great and sounds brand new. If I don't use if for a few days then try again, chances are it won't work and I have to use the power toggle / input toggle trick to get it to fire up again.
I enclose some pics of the circuit board for reference. I note that the diodes marked CR25 and CR26 have some scorching round them and the wire-wound resistors at positions R88 and R94 seem more chalky coloured than the others - so maybe a problem lies there? I don't know in which part of the amp these feature (preamp, power amp etc) so can't tell if there's an issue there.
Thanks to Enzo for sending me a schematic, but unfortunately I'm not that good at reading them so was hoping some kind soul out there might be able to help me out?
PS this is the export model as I'm in the UK and it's the stock M80 - no chorus. It's the grey face, red knob version in grey tolex not the one with the silver carpet covering!)