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Hello, I have a marshall DSL 401 amp. I've read alot of stuff on the internet about them and I just can't fix it. It always worked fine and I had it cranked one time and then the sound just wen't out of it. No pop or crack just fade to black. I checked the fuses and tubes and that did not work. I changed the tubes and nothing changed. I even changed the Bridge Rectifer and this still does not make a difference. The amp fires up fine power wise, just can't get any sound out of it. I've tested the speaker and it is fine. Any help Please!!
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Last edited by tboy; 05-01-2009, 06:38 PM. -
The last one of those I repaired had a blown 100K resistor R94. Otherwise you need to check for your high voltage. F1 may be blown. Are the filaments glowing on all the tubes? -
Yeah all the tubes light up and are evenly lite.Comment
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Wow,
yeah, it could be a whole lot of things. You didn't mention fuses, but I'm thinking you're past that.
Depending on your level of technical experience, I would begin by checking the power supplies. There are lethal voltages in these amps so if you're not sure, I'd leave it to the pros.
Do you have a meter? I'm thinking since you replaced the bridge rectifier & it didn't help, that you didn't first check for voltages present after the bridge.
Shot-gunning really won't get you to where you need to be. What is your level of experience in troubleshooting? It might be best to take the amp to a pro.
glenComment
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Yeah I'm diffently not a professional. However, I don't have much choice because the amount of professional's avaible to work on my amp is lacking. I live in Delaware not to many people work on them here, and the some who do throw everything they have at it for six months and up to a year until something works. I figured that I could try a few things with some help and see if I could come up with anything. Oh and yes the fuses were the first thing I checked.Comment
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Well Delaware ain't all that far from Phila and whatever is across the river in Jersey, Trenton maybe? Or even Balto. if the locals are not that sharp, take a ride. There are usually shops to choose from in the larger towns.Education is what you're left with after you have forgotten what you have learned.Comment
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If you follow the yellow wires coming from the standby switch they will lead you to the HV connector where the rectifier is located. There are also two caps connected to it . If the HV isn't present right there I would assume the caps to be shorted and the rectifer blown. You can measure across them to see if they are shorted but extreme caution should be taken as there's about 500 VOLTS DC on that connector. I've also seen the problem that Twist is talking about and this amp is a bitch to take apart to get to that rectifier. Lots of ribbon cables and just cables in general so you may want to take Enzo's advice here.KBComment
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DSL401
No output ?? Check vr12 should be a 200k[master volume control}
and is part of the bias circuitComment
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hello,
I don't see how/why a master volume control under any circumstances could or would be part of the bias circuit. This amp used 2 separate bias adjustments for each pair of power tubes. The master volume is definitely not part of the bias circuit.
glenComment
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Look again, Glen.
On the DSL401, the bias supply is adjustable by PR1. The dual 200kA pot at VR12 IS indeed the master volume. The bias voltage flows through it. it doesn;t scratch because there is little or no voltage drop across it due to the low current. But if one side of the pot opens, then that side power tubes lose their bias.
And inside the amp is the little three pin bias test point thing like on the larger amps, except on this one the two end pins are just wired together, not one for each pair of tubes.
However, to get no sound, both sides would have to open. Also, loss if bias won;t result in zero sound.Education is what you're left with after you have forgotten what you have learned.Comment
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Wow...that's weird.
you can see where they don't need to ground this master volume control as the bias voltage source is like a short to AC signal components.
I see where the marking 'Screen D' has a .01uf cap to ground from what looks like a tap on the lower section of the volume pot. I suppose if that were leaky it would cause all kinds of weirdness as you turn the pot slider closer to it. g
I guess they saved 2 cents on the 2ea 100K resistors they would have needed with this action. What will they think of next. thanx, gComment
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Yeah i got one off of fleabay [ ya bastard you knew it ! ]
the master seemed to cut in'n'out so took it apart and resoldered
the el84's and anything that looked funky , when i put it together
i now get barely any sound and the master seems to do nothing
[ well cuts out at both ends and gives a little in the middle ]
anymore idea's to help a brother ?Comment
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no volume on dsl 401 combo
To be clear , it would cut out but seem to be physicaly related to the
master volue control , not nesscarily time or heat , although i never ran
it long enough , so maybe .
i took it part and although the solder joints seemed o.k. i went over them
including the master volume and now i have no level at all , except for
some leakage sounding bleed when the master is in the middle .
any help is appreciated , where to turn next , is it heat , bias , physical ?
tia regards GregComment
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So replace the master volume control.Education is what you're left with after you have forgotten what you have learned.Comment
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Well , yeah thanks, that's on order
still not conclusive if it's the problem
but was hoping someone had delt with that exact thing
as they seem to have issueComment
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