Carlsbro GRX7, very distorted-transistors?

[Pure Liquid]

Hello all, im looking at a Cralsbro GRX7 powered mixer, ive seen the other two threads on this forum but their problems are not the same as mine. Basically it all started when a friend borowed the amp and brought it back saying it was crackling. When the gain and volume are both barely above one the amp distorts badly.

So far ive checked the mixer side of the unit with an other amp and thats all seems to be fine at high volumes. Power in seems fine at the transformer and there + and - 70vDC. Took a look at the amp and saw that the solder around the transistors, and a few other parts, had turned a little brown around the edge (is that what dry joints look like?) Ive had the transistors (MJ15022) off and checked them and they seem fine. I resoldered them back in and went over some of the other bad looking solder joints. But still the distortion is occuring.

Can anyone advice what to look at next? Is it worth replacing the 4 transistors?

Many thanks Terry.

[Enzo]

The brown stuff is probably residue from the soldering flux, and is not a problem.

I doubt your transistors are bad, especially if they test good. However there are other transistors in teh circuit. I would test every transistor and diode first. DOn;t remove them, just test them in place. If one checks shorted, pull it and retest. If one checks open, there is a good chance that it is.