So my DSL 100 (JCM 2000) died today...

GuitarIV

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Whats up guys, hope you're all doing fine.

Well the dreaded bias drift issue hit me today at rehearsal. My DSL 100 is from 2004 and has been reliable ever since I got it used, I swapped out the Poweramp Tubes about a year ago and biased them and everything seemed well and stable.


Today however I set up my rig, turned the amp on and after a while I had a low humming static noise that was slowly getting louder whilst my guitar signal was losing power until the amp itself lost power. My power switch pilot light went out.

So I ran to the amp, flicked the switches off and just caught a glimpse inside to see one pair of my tubes glowing red like crazy whilst the other ones were cool and gave off no light.

Now I knew this day would eventually come, I was hoping I had a specimen without the problem.

My question is what do I do next? I know one can order a replacement board and the stable bias mod as well, I just wanna make sure that'll fix the issue so I don't throw any additional money down the drain.

The amp has sentimental value to me, my parents bought it for me when my Valveking died. Otherwise I would have gotten rid of it a while ago as my JCM 800 is every bit Marshall I'll ever need.

Cheers!
 

PelliX

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Now I knew this day would eventually come, I was hoping I had a specimen without the problem.

You did... but this can happen indeed.

My question is what do I do next? I know one can order a replacement board and the stable bias mod as well, I just wanna make sure that'll fix the issue so I don't throw any additional money down the drain.

Well, perhaps we should identify the condition of the current board first. Chances are you might only need the bias mod... some gutshots (both sides of the board) would be appreciated.
 

GuitarIV

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You did... but this can happen indeed.



Well, perhaps we should identify the condition of the current board first. Chances are you might only need the bias mod... some gutshots (both sides of the board) would be appreciated.

Hey man, today is already late (it's midnight in Austria) so I'll try to take some pictures tomorrow or this weekend and then post them here :)
 

Gunner64

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I would monitor bias at pin 5 and see if it does drift. If so, I would replace the bias pots first, and see if the condition persists..and if yes, the Dr. Tube stable bias kit is a well thought out fix, and pretty economical if you can do the work yourself.
 

Dogs of Doom

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my bet is that either R6 or R9 (or whatever they are on the DSL) blew out & it's pushing volts to 1 set of power tubes, instead of millivolts, making them red plate...

edit:

R54 & R68?

1646955556948.png
 
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Gunner64

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Aren't they just for measuring at the test points?
 

Pete Farrington

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my bet is that either R6 or R9 (or whatever they are on the DSL) blew out & it's pushing volts to 1 set of power tubes, instead of millivolts, making them red plate...
If a cathode current sensing resistor blows, or just overheats and goes high resistance, current flow is reduced or stopped altogether. Hence that can’t cause redplating.
If they’re no longer 1ohm, then the mV across them no longer corresponds to mA (of cathode current).

However, a redplating valve can cause its cathode current sensing resistor to blow.
 

Purgasound

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Those older ones are time bombs. Once the board becomes conductive that's it. There's really no sense in trying to chase your tail on this one. You'll end up swapping parts out and modifying the bias circuit but nothing short of replacing the PCB is going to fix that. That's the easiest route but the caveat is even the new boards can develop the same problems as they didn't really change the layout, just the board material.

The alternative is to build a new bias supply on a secondary board and mount it on the unused section of the FX loop/output jack board. You also have to hollow drill out the bias pin on the PCB for all the output tubes. This is a fairly involved process. I've gotten these amps after 5 or 6 techs have already been through them and by then the owner had already spent a small fortune in bench fees for no one to actually fix the problem.

If you can get the stable bias kit from Dr Tube that's probably the best bet. I have made my own small eyelet boards to do this but it's only because I had to figure it out at a time when Dr Tube didn't have the kits available.

The main part that many people over look is that the PCB conductivity increases as the temperature rises. If the tech's aren't bench testing the amp wide open it may never go into fault. The amp can also work for up to 20 or 30 minutes before the tubes start to drift out of control so the repair person has to be aware that this requires extra time and effort to diagnose. This is why they keep coming back in for repairs. A few components get swapped, the bias is adjusted, the amp is jammed on for 10 minutes and sent back out the door.

Seeing as how a matched quad of EL34's is doubling in price since last month and their availability is becoming more scarce by the minute, I wouldn't risk a questionable repair. Get it done right and good luck!
 

Blh4216

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Whats up guys, hope you're all doing fine.

Well the dreaded bias drift issue hit me today at rehearsal. My DSL 100 is from 2004 and has been reliable ever since I got it used, I swapped out the Poweramp Tubes about a year ago and biased them and everything seemed well and stable.


Today however I set up my rig, turned the amp on and after a while I had a low humming static noise that was slowly getting louder whilst my guitar signal was losing power until the amp itself lost power. My power switch pilot light went out.

So I ran to the amp, flicked the switches off and just caught a glimpse inside to see one pair of my tubes glowing red like crazy whilst the other ones were cool and gave off no light.

Now I knew this day would eventually come, I was hoping I had a specimen without the problem.

My question is what do I do next? I know one can order a replacement board and the stable bias mod as well, I just wanna make sure that'll fix the issue so I don't throw any additional money down the drain.

The amp has sentimental value to me, my parents bought it for me when my Valveking died. Otherwise I would have gotten rid of it a while ago as my JCM 800 is every bit Marshall I'll ever need.

Cheers!
If you can get the JCM 800 English. DSL may like the sound but asian quality kinka no good once the go. If you can't fix it not worth money. Hold one to the tubes if they good? Real JMP MK II or JCM 800 keep for a lifetime. Can't afford, try one of the high end kits. Or, the should be plenty DSLs on the market. Sorry dude, that's a bummer but the latter mentioned marshals are keepers. Good luck 🤞
 

Franksamps

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I have repaired 2 of these and it got expensive. On one built in 1998 I changed the grid stoppers on the power tubes, the burned 1ohm bias test resistor, pulled the main board and drilled out pins. It really didn't do all that much, BIAS was still unstable. Eventually I removed the inner power tube pair and it ran better, cooler. IMO, without relocating the BIAS board the heat at that location (may) render the current bias board unstable, the little bias trimmers may be to blame. Running the amp half power, I have not gotten a call back yet. On the 2005, I just pulled V6 and 7, and all is well, so far. Replacement boards (incl. BIAS) are not available (to me) so that option was out. I know running an amp like this at 50W is heresy but whatever works.
 

Ampkeller

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Hi,
I have done the stable bias mod already 5 times successfully using the add-on board from Dr. Tube in the NL.
I live in Austria, too (Tirol to be more precise) so if you like I could do that for you.
Just google ampkeller for my homepage and contact details.
Best Regards,
Hajo
 

Dave O

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The bias drift issue in the DSL amps were from 2003 and back. Supposedly fixed from there forward. If your tubes are red plating you have a different issue. Even if it were a confirmed bias drift issue the replacement PCBs are not always the answer as some in my feild have said even in replacement of the main board the issue came back. I personally can't say anything about the DrTube board as i have not tried them. Dolve your tube issue, that is first and foremost. Then move to the bias if you think that is it. Do not jump ahead of yourself and do unnecessary things that may not be your problem
 

Rob Hoopes

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Whats up guys, hope you're all doing fine.

Well the dreaded bias drift issue hit me today at rehearsal. My DSL 100 is from 2004 and has been reliable ever since I got it used, I swapped out the Poweramp Tubes about a year ago and biased them and everything seemed well and stable.


Today however I set up my rig, turned the amp on and after a while I had a low humming static noise that was slowly getting louder whilst my guitar signal was losing power until the amp itself lost power. My power switch pilot light went out.

So I ran to the amp, flicked the switches off and just caught a glimpse inside to see one pair of my tubes glowing red like crazy whilst the other ones were cool and gave off no light.

Now I knew this day would eventually come, I was hoping I had a specimen without the problem.

My question is what do I do next? I know one can order a replacement board and the stable bias mod as well, I just wanna make sure that'll fix the issue so I don't throw any additional money down the drain.

The amp has sentimental value to me, my parents bought it for me when my Valveking died. Otherwise I would have gotten rid of it a while ago as my JCM 800 is every bit Marshall I'll ever need.

Cheers!
Two years ago I had the exact same problem with my DSL 100 made in 2001, did all of the research here and on youtube. Decided on the bias board mod, which was relatively easy to install (most time consuming part was labelling all connections) Put in a new set of Tungsols all around (sadly now unattainable) set the bias ONCE at about 75mv. I play it for an hour everyday in a garage that reaches 98 in the summer and 40 in the winter and that amp sounds better than it did new, and the bias is rock solid
 

FogDweller

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Years ago I also had problematic JCM2000. I sold it as is, bought my first JCM800 (1987 year 2204) shortly thereafter, and never looked back. There’s a lot to be said about the relative simplicity of the earlier circuits.
 
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SORRY for you troubles, man.

I bought one of these TSL 100 heads and it had already been fried to a crisp. I have an engineer buddy who was able to repair the board (bias mod and a few other things) and it worked fine. Problem is I can't leave well enough alone so I replaced the PCB myself and then it was a dependable monster. It's tedious but if you are meticulous and pay attention you can do this yourself. There are plenty of sources online to help with the connections, but I made my own diagram. And I'm not a skilled technician by any means.

I recommend a new board then you have a more stable product.
 

coldsteal2

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when I sold mine to a guy on Ebay, after an hour his blew up, i had to send him money back, Blew a transformer and fried some wireing
bummed me out him also
 

TimB

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You don't need a new board unless it is turned black. Brown is OK. The conductive board theory is wrong. Marshall uses the same fiberglass as everybody else, but no other brands or models are ever accused of having conductive boards. The bias drift does cause the board to run the tubes hot and they overheat the board, but that is NOT the root of the problem.
The root cause of the bias drift is the charge pump circuit in the bias power supply. There are two 22uF/50volt non-polar capacitors that supply the bias voltage. The charge pump is used because you can get a higher voltage out of a charge pump circuit than normally would be available from a rectifier. The downside is that it is a high failure rate circuit on any amp. The capacitors charge and discharge completely 60 times a second. This is very hard on the electrolytic caps. They like to be charged and stay that way. They are C43 & C44 on the TSL. They are C36 & C41 on the DSL models.
These caps don't show any visible signs of leaking or pop their tops. A measurement will show low values however. When they fail, they slowly heat up and lower their output voltage to the bias. They should be replaced with 63 or 100 volt caps with a high ripple current rating if you expect them to last very long. I replace them as a matter of maintenance on every one that runs across my bench whether they are showing drift or not. They all measure low.
 

Gunner64

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Imo the bias drift wouldn't be an issue if they had the ht and the bias traces separated by more than 2mm..that I feel is the main cause..and it seems more prevalent in climates with higher humidity.

There are guys with these amps who gig them regularly and never have had the drift issue, but I feel when humidity meets close b+ and bias traces the fun begins.

You could just simply have a shorted tube..it happens, or like I mentioned earlier compromised bias pots. It doesn't automatically have to be the dreaded drift condition. Rule out all other causes first. Don't just throw parts at it...Proper diagnosis is critical when working on any amplifier. It may have the dsl-itis..it may not.

That Dr. Tube kit works very well, and is easy to install. From the time I sat the amp down on my work bench to completed repair was a bit over an hour. They tell you to remove the board but I'll tell you you can just unhook enough shit to gain access, and unhooking all 5,000 connectors is not neccessary if your handy. Probably saves a good hour of time unhooking, labeling ect.

And Don't forget to fix the speaker jack ground issue as well.
 

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