My cherished Mark IIC+ has developed a nasty illness. When notes are played hard within a tone or two on either side of A (at least the first two octaves) there's a nasty sound that I can only describe as sounding almost like a really nasty raspy sound that fades back to a normal tone. It happens on both channels. I seem to recall reading something some time ago about what certain notes crapping out might indicate, but I can't for the life of me remember what it would be. These amps are a bit of a bitch to work on due to the fact that there are a few circuit board jammed in there IIRC and I don't have a schematic (not would I attempt the repair unless I was given VERY explicit instructions by someone that really knew what they were talking about. I'm just trying to get an idea of what the problem might be and what I'm looking at in general costs to know if I'm going to need to sell something.