How I fixed my DSL401 Overheating Problem

[okney1lz]

Felt like sharing, here goes.

So I kept having the typical overheat problem that unsolders the rectifier.

Here's how I fixed it:
How I fixed my DSL 401 overheating problem:

First I located the problem. The stupid little rectifier that heats up and un-solders itself. You'll know you have this problem if when you flip the amp upside down it starts to work again.




Next I drilled a hole directly through the center of the rectifier.



I had a heatsink from an 800 MHz Athlon computer chip laying around. So after about five minutes with a file and a hack saw I had made myself a custom heatsink for the rectifier.



I applied a generous amount of ArticSilver heatsink compound.



And then installed the heatsink with a small machine screw and nut.
I used to insulator on the bottom to protect the PCB.



Here's the finished heatsink installed:



Next I tied into the power switch with some 14 gauge wire to power two 110 V fans. I wired the fans to come on as soon as the main power switch is turned on.



Continued Below.....

[okney1lz]

Rest of it....

I drilled a hole next to the transformer and inserted a grommet to facilitate routing the wires outside of the case.



I installed two insulated spade connectors to allow easy removal of the back shield in the future. For right now I mounted the fans with a couple PC fan buttons and two zip ties. In the future I will more permanently mount the fans.



Here's the finished product:




Like I said I just wanted to share this information as this procedure seems to have cured my problem of the DSL 401 losing output after it heats up.

Please feel free to add any input or critique my methodologies in any way you see fit. I'm curious to know if people in the form feel this was a good fix.

[Enzo]

Hi, welcome to the place.

Marshall heater rectifiers have been a trouble spot for quite a while. Personally I think they get resistive becuase the leads on the bridge component were never cleaned properly. So the joints heat up. One has to wonder why that bridge would get so hot conducting nine tenths of an amp - the draw for three 12AX7 heaters.

Component leads themselves make pretty good heatsinks. I think if Marshall had left the bridge up off the board a half inch, and made the pads and traces to the thing a little wider, they would not have had this trouble. Well, that and cleaning the crud off the legs in the first place.

[Mars Amp Repair]

Welcome, too!
I agree with Enzo, I usually just replace the bridge & leave it about 1/2" off the board while doing my best to fold over the leads. It's a bit difficult on this larger bridge.

However, your solution with the heatsink would do the job & then some! glen

[Humanlike]

Can i have the rectifire issue if:
* Amp is giving out very low level sound when volumes are maxed.
* All the tubes light up.

First when i had the problem, it magically fixed itself overnight. Now the amp has been quiet for a week.

built year 2008

[Mars Amp Repair]

Hello humanlike,
It's probably best to start a new thread for your issue, so folks will be alerted to it, rather than stumbling on it at the end of this thread.
Possibly a bit more info on the symptoms would also be helpful for us to try & pinpoint your problem...glen

[2308to]

Wow! I hope this takes care of the issue now:-)

Felt like sharing, here goes.

So I kept having the typical overheat problem that unsolders the rectifier.

Here's how I fixed it:
How I fixed my DSL 401 overheating problem:

First I located the problem. The stupid little rectifier that heats up and un-solders itself. You'll know you have this problem if when you flip the amp upside down it starts to work again.




Next I drilled a hole directly through the center of the rectifier.



I had a heatsink from an 800 MHz Athlon computer chip laying around. So after about five minutes with a file and a hack saw I had made myself a custom heatsink for the rectifier.



I applied a generous amount of ArticSilver heatsink compound.



And then installed the heatsink with a small machine screw and nut.
I used to insulator on the bottom to protect the PCB.



Here's the finished heatsink installed:



Next I tied into the power switch with some 14 gauge wire to power two 110 V fans. I wired the fans to come on as soon as the main power switch is turned on.



Continued Below.....

[Prairie Dawg]

Welcome, too!
I agree with Enzo, I usually just replace the bridge & leave it about 1/2" off the board while doing my best to fold over the leads. It's a bit difficult on this larger bridge.

However, your solution with the heatsink would do the job & then some! glen

I do not think I would use a through bolt to secure everything through the board as that could tend to preload the circuit board and (possibly) induce cracks.

I did the same thing on a Marshall only I raised it 1/2 inch above the board and installed a small Rat Shack heat sink with a threaded insert.

In fact you can buy this very diode bridge from Rat Shack for about three dollars.

[Alex R]

Hi okney. Neat job, and thanks for going to all that trouble with the pics. But I'd be a bit concerned about the hole in the board too. Bit close to a trace there, as well as the stress issues.

[Mars Amp Repair]

Well as a servicer in business, while this is certainly a viable solution (provided you didn't 'preload' the board with the nut), as a service organization you have to find an profitable balance to what is adequate & effective vs doing the MAX that you can to preclude an issue like this.

We've repaired many of these amps as well as the JTM60's with similar issues by merely xnging the bridge to an 8 or 10amp version & standing it off the pcb by about 1/2" (as many have mentioned), and have had no rework issues in the 5yrs we've been performing this mod.

As far as adding fans (given our experience with this model over the years) if feel the fans are wayyyy overkill. By 'modding' the bridge & properly biasing the amp we find they run just fine with everything else left as stock.

So, personally I feel that although a heatsink is certainly a good fix for the bridge issue, as a servicer in business we tend to stick with what's been proven over a length of time to work as well as keeping the repair economical for the cust as well as profitable for us.

It truly is a balacing act sometimes, but good ideas for you own personal amp for sure. glen

[pecorporation]

I agree with Enzo, why is such a large rectifier (for such a small job) heating up in the first place?

[Prairie Dawg]

Well as a servicer in business, while this is certainly a viable solution (provided you didn't 'preload' the board with the nut), as a service organization you have to find an profitable balance to what is adequate & effective vs doing the MAX that you can to preclude an issue like this.

We've repaired many of these amps as well as the JTM60's with similar issues by merely xnging the bridge to an 8 or 10amp version & standing it off the pcb by about 1/2" (as many have mentioned), and have had no rework issues in the 5yrs we've been performing this mod.

As far as adding fans (given our experience with this model over the years) if feel the fans are wayyyy overkill. By 'modding' the bridge & properly biasing the amp we find they run just fine with everything else left as stock.

So, personally I feel that although a heatsink is certainly a good fix for the bridge issue, as a servicer in business we tend to stick with what's been proven over a length of time to work as well as keeping the repair economical for the cust as well as profitable for us.

It truly is a balacing act sometimes, but good ideas for you own personal amp for sure. glen

Interestingly enough the replacement Marshall item can be purchased for about 1/3 the price, or if you're in a hurry from Radio Shack for about three dollars.The original bridge is a 10 amp number-and I too wonder why they thought it needed that much in reserve. The Rat Shack bridge is 8 amps but that seems way more than sufficient for the job.

On the one I did I used a heatsink-don't forget the heat sink compound!-and it got pretty warm to the touch. I don't think there is such a thing as too much cooling air.

[Johnh]

Ive done similar things to my DSL401, which is a 2005 model. The issue with the rectifier is that, although it is nominaly rated for 10 amps, that only applies if it is kept cool. By 150 degrees C it has no capacity. Its heated up by the current running through it, plus being baked by heat from the tubes beneath.

I stuck a small heatsink on top with thermal cement, which avoided needing to remove the pcb to bolt under it. If you are replacing however, then I agree that longer leads are better, so less heat is conducted down to melt the solder, and also extra cooling is available on the underside of he rectifier.

But Ive also added fans because I considered the amp was getting hotter than electronics likes to be. Maybe it was designed that way, but it still seemed excessive, and fixable. I also did two mains fans, wired similarly as described here, except that I wired them in series so they each get half the voltage. That way they are very quiet. I believe that some other amps with 4xEL84 also have fans, as designed, such as Peevey Classic 50

All works fine now

John

[bluesfreak]

I had 2 of these DSL401 comin in for exact this failure and I went a bit ahead, I soldered some leads to the original pads and connected them to the recitifier now mounted on the chassis using it as a heat sink... worked also in some 900s SLX where the rectifier is endangered by a too large cap (spec says max 5000µF for the cap, Marshall puts a 10000µF in there ?!?)

[joenooch]

Hello,

Great thread!
My 401 was built in the early 2000's and in 2006 I had the rectifier replaced and resoldered for the same problem described.

However, in recent months another problem has occurred and I'm not exactly if it's the same problem or something different: the amp will cut out (not fade, but totally cut out.) However if I put the amp on standby for a few seconds and then take it off, the sound is working again, OR if I increase the master volume knob to about the 1 or 2 o'clock position, the sound will return. This problem tends to only happen when the volume is low and doesn't happen with the volume is high.

Any suggestions?
Thanks!