Need a Schematic for a Marshall DSL40c

[JustMike]

 I was experimenting with using it as a slave amp by running the line out of an attenuator into the input. The sound was very trebly and I ended up turning the treble on the DSL (slave amp) all the way down to make it sound reasonable.
 After that experiment, I plugged the guitar directly into it and now that same channel (Green Crunch) sounds very muddy.
 I've read that these amps were very trebly at low volume and I never had this issue with mine which I got used by the way. Maybe this was a preexisting condition that I pushed over the edge by a level mismatch?
 Also, the OD channel does not have this issue. It sounds as I believe it should.
 Need to start tracing the problem...Thanks!