There I was thinking I would be having an easy day.. a few amps fixed and I was looking forward to a beer on a beautiful afternoon...until a Marshall DSL15c has visited. Blown mains fuse..ok replace that and test the amp...no good...check power tubes...both are destroyed internally...white powder everywhere...replace power tubes and test . Weak clean channel..ok replace V1 and test. All good for a few minutes until I smell trouble ..the new power tubes are cooking. Pull amp out of combo box and check plate voltages...419v on each. Check bias voltage with power tubes in....hmmm...49volts positive...turn the trim pots...nope only increases the positive bias voltage. Remove power tubes and recheck bias voltage...18 v negative on one side of the trimpots but zilch on the other side which goes to small electros. The bias electro caps appear to have gone to god and killed the bias voltage. Noticed a couple of resistors have been replaced without the board being removed ( the board is a pain to remove )..they turn out to be part of the bias circuit but I have no idea if they are the original values. Removed the electros and reassembled the beast and bingo bias voltage returns and can be adjusted through the expected range via the trim pots. Checked the electros...all 4 gone bad ! Now it's a weeks wait for the new 10uf 100v electros to arrive by mail/courier.. I don't have any small enough in size to fit. I would have liked to been able to quickly check the circuit diagram rather than spending time figuring out what components are in the bias circuit.but, Marshall, being the lovely people they are, refuse to give any schematic for this (or any other ) amp so beware of any recent marshall amps that you you cannot find a schematic for on the web...and that goes for fenders as well as they have decided to be tossers regarding schematics as well. Ok Now it's beer o'clock !