Marshall MG250DFX Notes suddenly die on distortion channel

[Hawk]

The notes on clean channel decay normally, but not on the distortion channel. Instead they sound for awhile then suddenly stop as if being sucked out of thin air. Something is damping the natural decay of the notes...any suggestions? Transistors? Caps?

Also, using my scope and a 1 KHZ signal injected, and the Distortion Signal selected, the signal is very distorted on the Scope. Of course to me that makes sense as this is distortion, but what kind of distorted signal should I be seeing on the Scope? There is nothing as readable as a sine wave with some distortion on the wave, or signs of saturation or cutoff, just a wierd distorted signal which looks the same at all volumes, just larger and smaller values of the originally crazy signal...does this have a lot to do with the first three lines of my query?  thanks for reading this!

[DrGonz78]

Just got to say that all of these posts should be in one thread. Personally, I am having trouble following three separate threads that involve the same amp.  8|

[DrGonz78]

To help a bit you might try using a cheap DIY made signal tracer to be able to hear the signal as it travels through the preamp. Sometimes looking at a scope does not tell you what your ears are missing. Also, record some guitar parts and play them in a loop to be able to reproduce the symptom on the dirty channel. If the symptom appears right at R8 then perhaps it is a bad clipping diode. Best regards and sorry for the bitnichy comment early.  :grr  :lmao:

[Hawk]

No worries. I'm new so will definitely use the one thread for the same amp. I will take your advice and create some guitar loops to inject into the amp and signal trace. Also, I'll check the LED's to make sure they measure correctly (looks like I'll have to take the board out and measure from underneath--too bad they make these things so hard to service!)

I noticed that D11 is O ohms in both directions and is charred. Not sure if that has something to do  with it but that can't be good. Later today I will replace the diode and see what, if any, difference I notice in sound. From theory  I'd say that this diode will accept both the neg and positive of the ac wave and will always be "on" as it has no resistance in either direction and therefore no forward voltage drop. Does this create AC on DC line?  that can't be good, Hmmm.....