Marshall DSL40

[Rockranger]

Hey folks,
    A friend of mine asked me to look at his DSL 40 combo(I build a couple of small tube amps a few years ago). I never really looked at a modern amp or a amp that wasn’t hand wired. Anyway I’m having trouble finding a schematic for this amp and I’m kind of lost.
     The amp would play fine for 5 minutes and then start crackling and then loose sound all together, I opened up looked it over closely and couldn’t find anything obvious. I then replaced all the tubes with known working tubes and known working cable and still had the same problem. I then managed to get the main board out and I reflowed all solder that I could and cleaned all the connectors and still had the same problem. No sound on any of the channels! While testing voltages I would get a crackle through the speaker when testing V4, V6 and V7 (there is no V5) but no crackle when testing V1 V2 or V3.
V1
Pin1- 169 VDC
    3- 1.25
    6- 228
    8- 1.73

V2
Pin1- 268
    3- 2.77
    6- 236
    8- 2.01

V3
Pin 1- 205
     3- 1.31
     6- 338
     8- 206

V4
Pin 1- 108
     3- 15
     6- 109
     8- 15

V6 and V7 plate voltages are 160 VDC.

     I am definitely not a repair guy or a Marshall guy but this guy has a gig Friday and there is no where close for him to take it to so any help would be greatly appreciated.

Thanks

[sluckey]

V6 and V7 plate voltages are 160 VDC.

Are V6 and V7 the output tubes? If so, find out why the plate voltage is so low.

[Rockranger]

Yes V6 and V7 are the output I’ve started looking into the low voltage, forgot that the standby switch switch was a pentode/triode setup at the high setting I am getting 423VDC sorry the low setting is 160

[sluckey]

Probably gonna need a schematic and pcb map to fix this. Your friend will likely need another amp.

[Rockranger]

Ok thanks sluckey

[SILVERGUN]

Check this out:
https://www.diyaudio.com/community/threads/marshall-dsl40cr-farting.331307/
The DropBox links still work. This might be a schematic that we want to add to the library. No idea how accurate these are to the amp that you are looking at but I've never seen these before.

[Rockranger]

Thanks Silvergun these could be helpful

[Swampertech]

Will this help?

[AlNewman]

I'm also interested in finding the schematic for it's little brother, the DSL5c, if anybody has one kicking around. 

[Rockranger]

Page 1 and 2 V5 links that silvergun posted are relevant to what I am looking at. At first I had sound from both channels for about 10 minutes then I would loose sound now I only have sound from the ultra gain channel before loosing sound, pretty much out of ideas for this one

[Rockranger]

Ok I’ve left this alone since before Christmas the schematics provided by silvergun are relevant, I have borrowed an oscilloscope and signal generator and have been able to find a signal on the first three tubes and nothing on v4. The last spot I’ve found a signal is r140 in the EQ section I’m having a hard time following where to go on the schematic after that. I do not have a signal on c45 or anything leading to master volume 1 and 2. Any help on how to follow the signal after the EQ would be greatly appreciated!

[SILVERGUN]

Man, that schematic is giving me a headache!
You might want to post little schematic clips as you go so the kids will be able to play along.


Just a random shot in the dark - but, if you're referring to V4 as the phase inverter, sometimes they will have signal in and out points at that juncture.
I would be inclined to check those switching jacks if that is the case.
Looks like that would be "loop in" and "loop out"   

[Rockranger]

Ok thanks will do and I’ll report back tomorrow, and yes v4 is phase inverter.

[SILVERGUN]

A quick way to diagnose is to just use a patch cable to jumper out to in.


But, if the loop itself is switchable (in or out) then switching it out of the signal path should bypass that section of the circuit and prove me wrong.

[Rockranger]

Awesome thanks

[Rockranger]

No luck with the jumper out to in .

[SILVERGUN]

Sorry to hear that.


One trick I would probably try just to hear the amp work and confirm my suspicions would be to bypass IC3 and DFX1 and just jumper the signal over from the last point you have it to the first point you don't. That's still not going to solve anything but it'll at least show you that you are on the right path.


again, 

[Rockranger]

Of coarse my problem is in area littered with micro resistors and points that seem buried and impossible to find, among these is a normal sized resistor r145 it was very hard to spot I do have a signal on r140 and none on r145 I’m suspecting relay 11:2 could be the problem?

[Rockranger]

I will pull the amp apart and check this out tomorrow, thanks for the suggestions silvergun if it’s not the relay I will do what you said! If it is the relay does anyone know where I can get a replacement that doesn’t take 3 months to come from china, it is a HFD23-012-1ZS 6 pin relay

[AlNewman]

Just a kid playing along, but you should be able to check the relay by measuring continuity between R140 and R 174?

[WiderGates]

I'm also interested in finding the schematic for it's little brother, the DSL5c, if anybody has one kicking around.

This is the newer reverb model DSL5cr (3 tubes)
DSL5c is very different (5 tubes)

[Rockranger]

Ok I was able to verify relay 11:2 is bad, I took the board out again and ran a wire from middle of classic volume pot to r145 and now I have signal on the volume pot side of r74 but no signal on the other side of that resistor, replaced resistor and still no signal on the loop in side. With loop in leg side of that resistor lifted from board I have a signal but as soon as it’s attached no signal, signal is not going to ground or anything so I don’t know what’s happening. Tried running the last known signal to other spots (loop out side r100, r68) and same problem as soon as it’s attached to the board no signal!

[AlNewman]

This is the newer reverb model DSL5cr (3 tubes)
DSL5c is very different (5 tubes)

Thank you, I couldn't find any info on these amps.  I remember when I first bought it in about 2015, there was a really good thread somebody started on a bunch of mods he made, and I couldn't find it again recently. 

Mine has 4 tubes, looks like it might be really similar, besides the phase inverter.  I see there's a lot of components marked DNF, I wonder if that means digital noise filter? 

Sorry Rockranger, didn't want to hijack your thread.

[WiderGates]

I see there's a lot of components marked DNF, I wonder if that means digital noise filter? 

No, DNF = did not finish

[PRR]

Did Not Finish is car-races.

Do Not Fit is 'don't put this part in'. Either they thought they would need it but didn't; or were paid 10 cents per part drawn so got a little ahead on the paycheck.

[AlNewman]

Did Not Finish is car-races.

Do Not Fit is 'don't put this part in'. Either they thought they would need it but didn't; or were paid 10 cents per part drawn so got a little ahead on the paycheck.

Haha, I need a job like that, just decide how much money I want to make and run with it.
That makes sense, actually, there are a lot of DNF parts in the lead gain channel, maybe they were different snubber circuits or whatever in case the amp started misbehaving.

Or actually maybe those parts are present in the earlier version...hmm...

For Rockranger, I've seen that those boards can become conductive.  Might be something to look into.

[WiderGates]

I'm also interested in finding the schematic for it's little brother, the DSL5c, if anybody has one kicking around.

Hello,
I have found the schematic for the DSL5c
It has 4 tubes not 5.

[AlNewman]

Hello,
I have found the schematic for the DSL5c
It has 4 tubes not 5.

Thanks WiderGates

[Rockranger]

Ok as recap on this thread, a friend was having no sound issues with his dsl40. Sometimes you could play for a couple of hours without a problem and then it would cut out. I put 1000hz on a signal generator and checked the ac voltage on the anodes and cathodes of the tubes and figured out the problem was around V3B, while not working V3 pin 1 was 82.7 VAC and pin 8 was 9 .57 VAC. Pin 1 is the feed and these 2 pin voltages should match and both be well over 50 VAC at least. I replaced R80 R82 and C56 and finally had a working amp again with matching ac voltages on pin 1 and 8. Played it for a few hours and heard some small crackling and popping like it use to do before it cut out. It never lost sound completely again but I’m still afraid I’ll give this amp back and there will be an issue. While this amp is still apart what else around V3B could cause this and what is worth replacing. Again silverguns schematics early on in the thread are relevant. Any suggestions would be greatly appreciated!

[shooter]

Haha, I need a job like that, just decide how much money I want to make and run with it.

 
get a job with GOV, we called 'em brother-in-law circuits when I was in the Navy.  every sub-system had some "mystery circuit"
Once we "jumped past them" the system came alive!

[PRR]

> matching ac voltages on pin 1 and 8

That's not right. Do you mean pin 6?

[Rockranger]

no pin1 and 8 match when working the guitar signal leaves this tube through the cathode.