Fender Steel King distorting

[DanC]

Hello All,

My Steel King has suddenly developed this symptom when playing through it:  buzzy distortion, lower volume.  I don't know if this has anything to do with it, but I had the wrong power adapter hooked up to my volume pedal when I turned the amp on.

When I opened it up, I noticed that one of the resistors looked burned (although it measured fine).  It is R119 in the first sheet of the schematic http://www.fender.com/support/amp_schematics/pdfs/Steel_King.pdf (R119 is located at A4) 

I replaced the resistor with the same value, but the distortion was still there.

Could someone suggest likely culprits?  The speaker, cables, guitar are not the problem.  Any help greatly appreciated.

Dan

[J M Fahey]

This won't be easy, may end up being real frustrating, because the amplifier is (unnecessarily) complex, the signal zigzags from board to board, there are some  "mutes" including an "effect kill", the classic tests involving effects send and return don't apply, because in this case they are *not* pre-out and amp-in, there are *lots* of connectors, and ribbon cables, etc.
Anyway hook some music in the input, send effects out to another known good amplifier, to check the preamp, and send some music to the effects return to check the power amp, although as I told you before, things are not that straight here.
I think this is one of those cases where the oficial service is recommended.
Truth is, here you need a signal generator and a scope to trace signal stage by stage.
Just for starters, you have a mute across Gain (Q1), an effects bypass across U9a (Q5), an FX kill and an FX Rtn kill (Q9 and Q11), a mute across Master volume (Q2), a switchable limiter across U10b, plus all those ribbons and connectors where signal goes through.
It's not a job that can be "remote control run " as others.
Sorry.

[DanC]

Thank you very much for taking the time to look at the schematic!  I'm afraid signal tracing is beyond my abilities so, yeah, I'll have to hunt down a tech.  Thanks again.

Dan

This won't be easy, may end up being real frustrating, because the amplifier is (unnecessarily) complex, the signal zigzags from board to board, there are some  "mutes" including an "effect kill", the classic tests involving effects send and return don't apply, because in this case they are *not* pre-out and amp-in, there are *lots* of connectors, and ribbon cables, etc.
Anyway hook some music in the input, send effects out to another known good amplifier, to check the preamp, and send some music to the effects return to check the power amp, although as I told you before, things are not that straight here.
I think this is one of those cases where the oficial service is recommended.
Truth is, here you need a signal generator and a scope to trace signal stage by stage.
Just for starters, you have a mute across Gain (Q1), an effects bypass across U9a (Q5), an FX kill and an FX Rtn kill (Q9 and Q11), a mute across Master volume (Q2), a switchable limiter across U10b, plus all those ribbons and connectors where signal goes through.
It's not a job that can be "remote control run " as others.
Sorry.