Marshall DSL 40C - clean channel dropping volume once amp is heated

[Danglin' Fury]

I am quite aware that the resistor is not the culprit. The BOARD DEFECT is. But the guy I talked to in California repaired several by replacing said resistor. I am also quite aware that I need to find what is causing the heat problem. I know it is a board defect and I was just trying to find out if anyone knew what said defect was and what Marshall did to the revised board. As was sussed out in this post, pre me hijacking it, a great number of people were trying to help this person. It came to light that the board itself has a manufacturing defect. They replaced his board. Now if you can get "Marshall" to tell you or myself what the specific board defect is, that would be super because it is obviously something that they thought would be more cost effective to replace said board rather than have a tech repair it, which I dont understand, unless the repair is so egregious that replacing the board is better. I'm just curious if there is anything I can do to get this guy's anp back to him by Saturday as a crutch until I can ACTUALLY repair it... I have no idea what the board defect is. Nobody will tell me... so I'm at a loss... I feel like I am pissing into the wind here.

[The Dude]

I would put the "bad board" theory out of mind and troubleshoot the amp like any other. If the resistor is getting hot, start by measuring voltages on both sides of the resistor to see what the voltage drop is. Go from there. Determine WHY the resistor has so much current flowing through it and why voltages are what they are. IMO, the whole "defective board idea" is only getting in the way of actually finding out what the problem is. I don't see any reason why standard troubleshooting procedures wouldn't be applicable- bad board or not.

[g1]

I am having the same problem the original poster is... he just happened to have his problem when Marshall was handing out replacement boards with the revision done... I'm a little late to that party.

Sort of but not exactly. Look back at post # 9. His 'hot spot' was around SW2, yours is around SW1 (R7 is on far side of SW1 in attached pic).
Maybe they were junky switches and they couldn't get good ones with the same footprint so they re-designed the board. Like Helmholtz said, the normal current through R7 is miniscule so if it is warming up, find out why.
It does sound like heating of the switches leads to malfunction in both cases. If it's SW1 in your case, you should be able to make it act up by heating the switch with a heat gun or hair dryer. And if R7 is actually responsible, it would obviously be warm to the touch which you can easily verify.