Very loud screech from a Fender Frontman 15R

[nitenurse]

Hi!, my Frontman 15R had been working ok until 2 days ago. On switching it on then, it immediatly started to howl extremely loudly. Even setting all the knobs to zero and unplugging the guitar made no difference at all. I'm comfortable with repairing most elecrtical items but electronics is a grey area for me. I've removed the circuit board but cannot see any obviously faulty components or dry joints. I guess the amp is "dead in the water" given that they are fairly cheap to buy. I just wondered if there was anything I could try to trace the fault as the amp is otherwise ok. Thanks.
Wayne

[J M Fahey]

Hi Wayne, ¿can you solder/desolder cleanly and read a schematic? Start by downloading http://www.google.com/url?sa=t&source=web&ct=res&cd=1&url=http%3A%2F%2Fwww.fender.com%2Fsupport%2Famp_schematics%2Fpdfs%2FFrontman_15G_Schematic_68F.pdf&ei=d1x5SuOpFNa_tgfw1OWWCQ&rct=j&q=Frontman_15G_Schematic_68F.pdf&usg=AFQjCNFsY8bdTcaavnRA4c7DaIGsf5nvNw
and check whether it fits your amp.
The schematic will be the same or *very* similar, but part numbers , such as C104, R75, etc. might change in different production runs.
Good luck.
J M Fahey

[nitenurse]

Thanks for your help. I'll take the circuit board out again as soon as I get the chance and compare it to the schematic. My soldering skills are adequate but I'm not so sure about my schematic reading! I've worked with various electrical plans in the distant past but these electronic ones look pretty complex and some of the symbols are a mystery to me. I've got a couple of busy days coming up but I'll strip the amp again on Saturday or Sunday.
Thanks again. More anon,
Wayne.

[nitenurse]

Dear J M Fahey, I've stripped the amp again and checked the circuit board against the schematic as you suggested. In the main the components appear to be the same but as I've got the "R" version there are also some differences  -an extra pot for the reverb etc., and I've got Auxillary inputs instead of an external speaker jack. Any suggestions as to proceed?
Thanks and best wishes,
Wayne.