SOLVED again: DSL40CR 20w stopped working?

Geno5150

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My DSL40CR works with the 40W setting, but nothing from the 20W.
Since the 40 is ok, I would say the tubes are ok reading another post, still tried guitar straight in to fx return. Same 20w silent, 40w works. There is a slight "radio sparkle" but I would take that as interference from the surroundings. The 40W stage sounds just fine.
Any thoughts what I should try is much appreciated.
I know a little bit of soldering, so not afraid to fix. First "gig" ever in a week so timing of this was not ideal.
Min did the same thing. The switch went bad. The tech replaced the switch and now it works great. Mine was u der warranty so it was covered.
 

Matopotato

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Min did the same thing. The switch went bad. The tech replaced the switch and now it works great. Mine was u der warranty so it was covered.
Thanks. I also still have warranty but buying over the internet has the downside of sending it away to, in my case, probably UK. I have asked though.
 

Matopotato

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Thanks all who chipped in! For me it was a first, but many of you already knew the answer.
Warranty meant sending it off for 2-4 weeks or more. So I was going to hand it in locally. 2,5 weeks, but I like yo support locals when I can. He has good rep a d experience. Thought that regardless it is good to have some spare tubes, so why not start there. So got a pair of EL34s (JJ Slovakia) at what equates to 82$. Imho ok all things considered.
Swapped and works as it should. "Static" gone. Keeping the old for emergency, but might get another fresh pair later on.
It now struck me how easy it was to bias them.
Previously the one kept moving about when left for a while. And really hard to set. The other was more stable and more resonding with less fidging all over.
Also read the old ones before the swap and the one I suspect being the faulty on was at high 40s close to 50.
Again suspicion only (since I gave up always rebiasing them) is that the one that broke was a bit defect to begin with and kept rising until it was in a bad area.
If so I'll tell the vendor although it will be hard to convince them of sending me anything at this point.
Does this make sense? Or am I lost in mindgames?
Also wonder which of the bias controls belong to which tube? Logically I'd guess same order. But faint memory says I read they were reversed.
I got word from the shop that EL34s from Marshall are the same as xyz, just branded.
Which power tubes would be different, to try out. Seems there would be 3 main strands.
Also he indicated that tubes influence on tone etc is perhaps less than many other things. To me it sounds great now, but i am "biased" by having fixed my problem.
Again, many thanks for help and putting me in the right direction! Saved me 2,5 weeks without amp 😁
 

Matopotato

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Apparently I spoke too soon. After enjoying 5 days of what felt very good, it is back to intermittently working on 20W setting.
Brand new tubes. No spakly/static/crackly sound on the 40W.
And bias loks very nice and stable at 37mV.
On 20W it is either 80mV ish (expected) or zero in both, which makes me suspect something other than the tubes.
Easiest is to blame the switch, but don't want to open up that section.
 

Max Gahne

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Sorry that new tubes didn't solve it. Looking at the schematic the standby switch selects one of two rectifiers/power supplies for the PI, OT and power tubes - but also to an optocoupler that appears to be in a circuit to select bias voltages. This might be why in 20W mode you're seeing 80mv at times and zero at other times. If you are able to probe the switch voltages you could see if the problem is in the switch - myself after tubes I first suspect a mechanical device. You could replace the switch yourself, they use spade connectors you can pull off. If the switch seems fine the problem would be downstream from it and could be that optocoupler bias circuit. If so that's probably best left to a tech.
 

Matopotato

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Sorry that new tubes didn't solve it. Looking at the schematic the standby switch selects one of two rectifiers/power supplies for the PI, OT and power tubes - but also to an optocoupler that appears to be in a circuit to select bias voltages. This might be why in 20W mode you're seeing 80mv at times and zero at other times. If you are able to probe the switch voltages you could see if the problem is in the switch - myself after tubes I first suspect a mechanical device. You could replace the switch yourself, they use spade connectors you can pull off. If the switch seems fine the problem would be downstream from it and could be that optocoupler bias circuit. If so that's probably best left to a tech.
Thanks a lot @Max Gahne for this.
The 0 or 80mV in 20W selection is 1-1 with "no sound" problem. I more added it as an indicator that the tubs get nothing, so they are unlikely the reason this time.
I am happy about the new tubes actually. And realize the old ones were probably off, at least one of them, so a change was due. Probably fromnthe beginning, but will not push that for now.

I suspect the switch as well so then I guess there were 2 faults present at the same time.
I handed in to a local tech. I felt prying the switch with my not so goog technique would probably end up with scratches etc. Anyway, he should be able to see if it is the switch or more stuff. If there is too much to fix, I will send it back to the UK shop.
 

Geno5150

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Thanks. I also still have warranty but buying over the internet has the downside of sending it away to, in my case, probably UK. I have asked though.
You dont have to send it away. Go online and find your local Marshall repair mine. I found one here in St louis.
 

Matopotato

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You dont have to send it away. Go online and find your local Marshall repair mine. I found one here in St louis.
Thanks, I did and I found the local one. Good rep, worked for many a guitar shop and more. Got my tubes from him in the first attempt. Only downside is there is no official Marshall repair in my city. Sending it to where I got it would be cheaper, only shipping, but they said 2-4 weeks, possibly up to 60 days.
 

Matopotato

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Ok, so solved a second time.🙂
It was the 20/40 switch where a "cramp" connector was not cramped hard enough to its wire. So wire did not connect properly. He now soldered it to its cramp.
I could have been more brave, openend and checked myself. But a lesson learned.
The local guy is good and I think you have to pay some to keep them in business. Next time (fingers crossed) it might be my only option.
Anyone who stumbles on this thread with similar symptoms:
New tubes
Check the switch
were my takes from this.

Edit: "crimp" is the correct word in English
 
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