DSL40C effects loop switch volume drop

[cruisemates]

DSL40C working perfectly until I push in the effects switch - then I get about an 80% volume drop.

Now, it only happens after the amp warms up. And at first I could "tap" the top of the amp and the full volume would return. Well, tapping doesn't work anymore and I KNOW it is related to the effects loop now (it only happens when I turn the effects loop button to "on")

Is there a singular tube that runs this loop or some other weak link? I would open it up but I can't find a schematic for these. Anyone know where to find one?

FYI: this happens whether I have things plugged in, or nothing plugged the loop. It happens when I jumper the loop. No matter what, if the switch is on the volume is gone.

Thanks for any advice

 

[Micky]

Clean the jacks and work the switch a few times to see if it helps.

 

[cruisemates]

Are the jacks TRS? so that one could get stuck in a bad position? The volume drop happens whether I have anything plugged in or not. I actually think the short could be somewhere else - because it used to come back to life if I tapped the top right side of the amp (not even near the jacks or button) but that is not working anymore.

I already shot the jacks & button with cleaner - I could "work the jacks" a little more. But it is CLEARLY a volume drop when the button is on, and volume comes back when it is out, so this is not intermittent - something has broken.

My old dsl401 was famous for solder joints that would get loose when the amp heated up.

But I need a schematic to see what might be in the circuit. I can see the gut shots here online - but that is really not enough.

 

[Roger Tyria]

See my post in the Official DSL page.
I think it's Relay 3?

 

[mickeydg5]

The jacks are TS, not TRS.
Try checking, cleaning and resituating CON2A & B.
If that does not help then it may be solder joint/connection, relay 3 or something else in the RETURN booster circuit itself.

 

[cruisemates]

Sorry - where (what) is this: CON2A & B. ?

Are those on the mini PCB with the switch?

 

[mickeydg5]

Good question. I do not have a DSL40C so good pictures would help.

It would or should be in the vicinity of the SEND and RETURN jack wiring to the board.

 

[cruisemates]

FYI for those who search. The small PCB that holds the EFX switch and jacks goes to another PCB in this picture below the other end of the 5-pin molex connector (with blue cables - the square piece with one large square IC and two smaller ICs - you can barely tell it is actually mounted about a 1/2-inch above the main circuit board).

Make sure THAT smaller circuit board is well seated. There is a row of about 10 pins on the left (in this pic) - push down on those. That was the problem in my amp. it is fixed now.

I hate threads that don't show a solution - so I came back to add this. THANKS EVERYONE for your help, I never would have seen that otherwise.

 

[USAPatriot]

FYI for those who search. The small PCB that holds the EFX switch and jacks goes to another PCB in this picture below the other end of the 5-pin molex connector (with blue cables - the square piece with one large square IC and two smaller ICs - you can barely tell it is actually mounted about a 1/2-inch above the main circuit board).

Make sure THAT smaller circuit board is well seated. There is a row of about 10 pins on the left (in this pic) - push down on those. That was the problem in my amp. it is fixed now.

I hate threads that don't show a solution - so I came back to add this. THANKS EVERYONE for your help, I never would have seen that otherwise.

That's the reverb. I have the schematics here but not open and no time to trace it right now. I don't know if there's a connection between the loop and the reverb itself but it may be part of the larger chain. If this was a Jet City amp, the loop circuit would insert just before the PI and a bad connection anywhere in between would definitely drop the volume out. If the reverb in our 40C's is in the chain with the loop, it's likely something similar happened to you. Glad you got it fixed (y) -Rod-

 

[cruisemates]

That's the reverb. I have the schematics here but not open and no time to trace it right now. I don't know if there's a connection between the loop and the reverb itself but it may be part of the larger chain. If this was a Jet City amp, the loop circuit would insert just before the PI and a bad connection anywhere in between would definitely drop the volume out. If the reverb in our 40C's is in the chain with the loop, it's likely something similar happened to you. Glad you got it fixed (y) -Rod-

I can tell you there is a cable coming directly from the effects loop switch/jacks to connect just below that reverb card, and in my amp it had become dislodged by about a 1/2 inch (all the pins on the left side had come out of their sockets and we just laying atop the connector). I had noticed that if I tilted the amp the volume came back on, then if I put it upright it went off again.

 

[USAPatriot]

Well you got it fixed, so that's what counts. Looking at your photo (I have my own set but haven't traced the entire path out yet) It looks like there's V4(PI) -> Reverb -> Loop -> Power stage. I'm assuming here that Marshall was smart and put the onboard reverb in before the loop. -Rod-

 

[jbull]

My 40C developed the same problem,
Tried the small PCB push and
the FX loop switch is still BIG MUTE switch.

Guess I'll take her apart once more use cleaner through next chance.

 

[jbull]

Okay first step should have been eliminating other variables.
I spent an hour touring on the PCB.

First thing to do is run a patch cable and push FX switch in.
If there's no volume loss it is not the amp it's pedal board or cables.

In my case it was planet waving patch cables that were doing it.
Wasted an hour on this as first thing I did was to Google it. Haha.

 

[Greatwhitenorth]

Okay first step should have been eliminating other variables.
I spent an hour touring on the PCB.

First thing to do is run a patch cable and push FX switch in.
If there's no volume loss it is not the amp it's pedal board or cables.

In my case it was planet waving patch cables that were doing it.
Wasted an hour on this as first thing I did was to Google it. Haha.

I've had the same thing happen. I spent half an hour trying to figure out why I had no sound with the loop engaged. It ended up the one of my pedal's 9V power connectors had come out. I played half of a jam without effects before I saw it. I could have saved a lot of time by doing the jumper trick.

 

[Micky]

The FX I/O jacks are connected to the mainboard by a 4-conductor connector and wires, CON2 a&b. Insure the contacts are fully inserted into the connector housings and the connectors themselves are pushed fully onto the pins on the board.

A small jumper between the in and out jacks should make no volume difference if working properly.

 

[cruisemates]

Thanks for tips guys. After I fixed mine once - the problem did pop up again. I hate to admit this, but my mom's old "Vogue Magazine" fix actually does work on this amp - that is where you find the right spot and smack the thing with your fist. If it didn't work, I would never do it, but it works every time, and I'm usually good for the rest of the night.

I just have not felt like opening the thing up again - but that molex connector trick just mentioned sounds like a good place to start next time I do open it up.

 

[Fabio Estevao]

I have same symptoms with my DSL40C, but the source of the problem was different.

My problem was in the R56, 470 ohms resistor. Since I powered up the amp, it warms up and starts to increase the resistance to 1M ohms.

Replacing the resistor, the problem was fixed. The R51 has the same function in the circuit, so it could happen on this component too.

 

[Tripp912]

Similar issue with my DSL40 - I ran effects thru the FX loop - when the amp gets warmed up good, I lose sound. All sound gone. Turn the amp off, let it go cold, take the FX loop out(off), turn it back on, let it warm up, I get sound thru the front pedals, kick the FX loop on, it will play sound fine....til it gets hot, then repeat...makes one wonder hearing similar issues with the FX loop