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

[Star_maker]

Is there any progress on the thread, since i seem to have the same problem

[mozwell]

DSL15, 40, 100 & 401 schematics
Hope they help
SW2 goes to link LK1 and to 10K R103, and connection "SW_CHANNEL" which goes to micro AT2313 (IC4)
Measure pin 16 of IC4 (or across R103) to see if this changes reliably when the switch is changed, If it does, it could be the micro IC4
Check the solder on LK1 & R103

You could also temporarily solder a switch between the +5V rail & LK1 & see if the amp switches reliably with that, if so, replace the switch SW2

Also, check the voltage on IC4 pin 11 to see if you are getting the right signal here.... (the micro may see this the AC supply is lost)....

[Tone Meister]

Is there any progress on the thread, since i seem to have the same problem

The amp had a manufacturing defect in the PCB. Marshall replaced the amp with a brand new one even though it was long out of warranty. They even paid for shipping both ways.

Sorry, should have posted this long before now, but I've been out on tour for a couple months.

[chaine]

The amp had a manufacturing defect in the PCB. Marshall replaced the amp with a brand new one even though it was long out of warranty. They even paid for shipping both ways.

Sorry, should have posted this long before now, but I've been out on tour for a couple months.

This sounds familiar... do you have any information about in which batch your amp was manufactured? Do you have any information (like a problem "name" or service ID or anything) about the actual defect, which others can use as a reference in communication with Marshall if they find themselves in the same situation? Thanks!

[Danglin' Fury]

Hey all... I know this is a necro thread, but I have one of these on the bench. This is the 3rd time. I "fixed" the problem twice by putting a 100k ohm, 10 watt resistor at R7, which I was told "holds" the switch for the clean/crunch... this last fix has lasted for a few months now and the dude is most definitely an active, gigging musician. I know these amps have had a board rev but as they do not sell these anymore, I need to know what the board defect is so I can help this dude out... I was thinking about mounting a small computer fan inside it to cool the board but that doesnt seem too practical as it is the DSL-40C combo. In at a loss and I'm tired of repairing this damn amp... LMAO! like I said... the 100k 10 watt resistor has lasted months now, but obviously it's not permanent... thanks for your input.

[DrGonz78]

Can you post a photo of the circuit board which shows the R7 100k resistor?

[g1]

There is an R7 shown on schematic from 2011 that goes to the clean/crunch switch. It is shown as 100K, 0.6W. It passes signal to the switch, but there is nothing that 'holds' the switch electronically.
I guess there may be other versions, but I don't see any kind of 10W resistor anywhere in this schematic:
https://music-electronics-forum.com/...etch?id=837569

[Danglin' Fury]

Lol! I replaced the .6 watt 100k with a 10 watt. I talked to a Marshall repair center in California, and he told me that yes, there was a board error and Marshall was replacing boards. Buuuut they did not have any more as they dont make the DSL-40C anymore. He told me that particular part, R7 (100k .6 watt) was to blame and it was getting excessively hot and it was affecting the switch. I asked him if I put in a higher wattage resistor if it would fix said problem. He said yes, so the first time I replaced it, i used a 2 watt. That lasted all of 2 weeks. 2nd time i repaired the exact same problem, it solved the issue for several months. And here we are again. Apparently the 10 watt resistor I installed STILL isnt permanently fixing the problem. Does anyone know what Marshall did to the revised board to stop this from happening? I dont know what else to do.

[Helmholtz]

Something is wrong here.
The R7 in the schematic only sees a small signal current and shouldn't get warm at all.

Please verify the schematic.

[Danglin' Fury]

Oh I agree... but when i replaced the .6 watt part with a 10 watt, it "fixed" the problem for almost 6 months of heavy gigging. And I cant find anyone that can tell me what Marshall did in the revision to fix said problem.
the guy I talked to in Cali said he put a scope on it and applied heat to that area, the signal started freaking out. He said to put a 2 or 3 watt resistor in there as he had repaired at least 15 with that exact problem. Well, I put a 10 watt in that place and it still isnt staying fixed.

[Helmholtz]

Did the failed resistors measure open?

[Danglin' Fury]

No they did not. The original 100k .6 watt measured like almost 500k if I recall correctly, but the 2 watt I installed and the 10 watt that is in there now measures 92.6 k ohms. This is very frustrating because I know that Marshall themselves said it was their bad... design error, manufacturing error, whatever. But their response was to replace the board with a new, revised board... but as I said, they dont make this amp anymore and they arent replacing the boards anymore either. Ans the customer really likes this amp so he doesnt want to get a different one so... here we are.

[Helmholtz]

I would take more than 250V to blow a 0.6W/100k resistor.

So if we are speaking of the same R7 as shown in the schematic, there must be a severe problem with the amp that you didn't fix with replacing resistors.

How did the problem show?

[Danglin' Fury]

The problem only shows when he is gigging. When I changed R7 to a 10 watt part, it lasted for almost 6 months. The amp works fine... except for this one problem of the clean channel, and the clean channel only, fading out to very quiet. And only with time and heat. As I said in my previous posts, the first time I replaced the resistor, I replaced it with a 2 watt 100k. That lasted 2 weeks... the 2nd time I changed the resistor to a 100k 10 watt part. The amp worked fine for almost 6 months... and the clean channel fading has come back again. Other than that, it sounds great. If the guy didnt gig with it 4 or 5 times a month, it might not be a problem. But he does and Marshall knows it is a bad board. I didnt mean to hijack this particular thread, but 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.

[Helmholtz]

... the 2 watt I installed and the 10 watt that is in there now measures 92.6 k ohms. .

So you replaced a good resistor. Should be clear that the resistor is not the culprit.
No matter what "Marshall" said, you need to find the root problem. Might be intermittent, maybe triggered by temperature or vibration.
Does a 0.6W resistor get hot? If so, find out why.