How to Repair Marshall DSL40C Tube guitar amp D-Lab Electronics 

Great repair, most would be surprised how well this amp sounds,thanks Terry!

Another great video and tutorial. Love the step-by-step troubleshooting skills and knowledge that you pass along to the community here. Keep it coming!

Great video Thanks! Brings back memories of my father in his tv & radio repair workshop for so many years. I wish I learnt more from him while he was still around. Now I have a vox nt50 with a dead pre-amp I'm going to attack in December so these videos are a goldmine of info!

Another very interesting video. With noise or gain problems it is always worth testing the valves first. Those components with very little solder are in ‘plated through’ holes. When they are soldered on a flow solder machine the do get properly soldered on the reverse side of the board, as do normal single sided boards. They do not need soldering on the top side. Cheers

Terry you are a genius at this stuff.

Incredible skill. Very inspiring to see a master of one’s craft.

Incredibly helpful and informative video!!!!! Great explanations in what you were doing and especially why. Thanks for sharing your knowledge.

Great video! Easy to understand. And it re-enforced my assumption on the v1-v4 positions. Thanks!

Thanks for the knowledge on the DSL40C. Learned a good bit watching this video.

Thanks Terry! The video shows the bad designs and cheap components that they are using that provocate the issues, nothing like the old amps

Seems like you always get the easy repairs. Or, you make it seem easy😊 I use left hand drill bits for extraction. Lots of time it grabs the screws and backs them out.

Great job Terry! Also, nice to see the old Labrador still around.

As Mr. Burns would say: "Exxxxcelent!". Very informative, thank you Terry.

You are a saint for working on these circus board amps. Bless you.

Neat walkthrough, Terry. Thank you!

Another good video as usual from D-Labs. I have one of these. It just so happens I checked tube bias yesterday, wherin it needed a minor tweak, one side a little high and one side a tiny bit low. I had never ever checked in the 4 years I have ownerd it. I came across a brand new Eminence Tonker 8 ohm a couple of days ago for a very good price and I jumped on it. Just finished installing it when I happened across this video. After seeing this video I think I might take a look see to verify good soldered connections on the board.

Another great video, you sure spotted the problems quickly!

Great job Terry. Seems to always be a lot of issue with this type of design. D-Lab to the rescue!

Killer attention to detail. Great video

Fantastic video. Very good explanation!

LOL! I had a real moment when you noticed c90, cuz I had seen it 30 seconds earlier. The suspense was killin' me...then...Bam! c90 fixed. Having a real fun time in solder school right now. Good stuff, thanks!

D lab. Another great job and diagnose!

Congratulations! Your channel is awesome! I wish there was a d-lab here in brazil! I've been having some "white noise" problems with my ampeg reverb rocket 212 tube amp :(

Excellent investigation work Terry! Wow, what a shoddy job from the factory..Just another example of why I dislike amplifiers with circuit boards.

Very good sleuthing Terry... always learning from you, thank you man....

"Drill it, tap it, mount it" I live by this philosophy everyday.

Thanks,Terry,for some more great troubleshooting tips! Thumbs up to your video Grapher as well! Any chance you could do a video on tweaking the audio of an old tube radio for high fidelity?

I picked up a DSL-40 that was significantly under 1/2 price (the only reason I bought it). It was "not working, tried new tubes, etc". Fixed a few bad solder joints and bam... it works. It's a nice amp but the circuit board bugs me... Left hand drill bits are your friend for screw extraction. "Battery;s are probably low" LOL It's always good to see your work Terry. I always learn something...

Yes! those types of repairs can be exasperating; "nice presentation Terry".

I learned some things today , wondering what soldering iron u mite reccomend that will last.? Seems i go thru em way to fast . Been using 40 to 6o watt with an adjustable voltage.for guitars n simple amp mods . Thx

Hi Dlab, wonderful video, thanks. I have a 15 month old DSL 40C and I just started experiencing a random drop in volume on my red gain channel followed by a shreaking high pitch (microphonic?) noise then it fades away back to semi-normal. I’m hoping this is just a failing tube issue. All tubes glow and I did adjust the bias on the EL34s from 41/26 to 38/38. Played great for 30 minutes then the problem intermittently returns. Bad 12AX7/ECC83s or bad EL34? Should I just replace both of the EL34s with a “matched” set? Would love to hear your thoughts. The amp doesn’t get moved around, sits in the same spot in my living room, no gigging. Thanks!

Great job, best video yet. I would like to see a video on how to set up and use you oscilloscope, I have one just like yours. but need some guidance

Love your work Sir !!................I just subscribed !

Great video, very informative. Thank you !!!!!!

Another great video Terry, As a guitar player I enjoy watching your channel, I wish I could send you my amps for repairs. do you get amps to repair from other countries ?

Great job Terry, I would like to restore a 40-year Zenith radio, I also fixed some American radio, like emerson

Confidence! That is what you have Terry! First thing I was taught in Tronics school was you have to have the guts to open a unit up to troubleshoot it! Speaking of Tronics school, were you in the Navy? Your vernacular sounds like the retired Navy electronic instructors I had in college. Love it!!! You do what I do, use a lighted magnifying light. Great video! Thankz

Terry - Taps are usually square-headed, and square sized 1/4' drive sockets are available, so if you needed to tap a hole down inside something you can just use 1/4" extensions and a regular 1/4" ratchet.

Amazing. You sir are a genius

Thank you my friend!

I think your dog wanted to go out and play with Rusty from Uncle Doug's channel

can i make my bias more hot just by turning thise things counter clockwise a bit

Hello Terry, one thing you mite want to try @ 5:31 is to use a left hand drill and back the old stud out.

Love your Video thanks so very much for sharing

I found that the power tubes hum when going bad, maybe the vibrations cause it for less life. Usually a year I get on mine and bias it at 32, most bias them too hot and causes issues and being a preamp distortion its all ya need:)

Great video! When I bought my first DSL 40C, it would sporadically cut out, returned it for another, and that one's been good thus far. I would like to know the serial number of the one in the video.

Howdy. I had a similar problem with my BK Precision signal generator. The signal levels and the frequecnies were all over the place. I bought it to do IF aligments but it became hopeless. I spayed contact cleaner on all switches and potentiometers. Nothing. I happened to watch a video where another pro located the source of parasitics by pushing wires with a wood stick. So I did that. And eventually I observed the signal coming on and off pushing at the corner of an auxiliary circuit board. Bulls eye. A mounting screw providing ground was out of thread alignment and had not got tight. Luckily, at the factory, they obviosly used torque limiting drivers so the thread was not completely destoyed. I loosened it and carefully got it thread aligned and tightened. Back in business. Regards.

Dear Sir, I wonder why you did not use a ground lug under that screw, just saying... Hats off to you for the deep intervention you went into...

I wish i could hear the solution...learned alot btw thanks! 1 other thing, how (where) did you hook up the scope to test?

I have two Marshall TSL60 amps. They're complicated circuits. But they sound great.

love your videos. Seem like you will have two paths from the same connection. One from the screw and the other from the new lead you made to the chassis. Thinking it might cause a ground loop? Then again I am just a noob.

Right on Terry! ;yes it certainly is captain obvious a good perc;entage of the time like here at least part of the problem . love you easy going style of displaying your stuff. thx. again. Terry enjoyable watching .

I cringe whenever a DSL, TSL or a 410 come in. They are a pain to work on. As Terry implied, those pots are a disgrace to a once proud manufacturer like Marshall. Its shows what happens when accountants run a music company instead of musicians and engineers. Good job Terry. I like hearing Mrs Lab in the background with her directions. :-)

Keep the videos coming !!!

thanks, I just bought one of these for cheap beacause it hums and buzzes pretty badly how do you discharge this amps capacitors?

terry why did't you remove the stand off and drill n tap it outside of the chassie? was the bottom fastner bradded over?

Hey Terry, I'm trying to repair my DSL15C but I can't find the problem, can you help me?

Part of the reason for the bad solder joints is these boards were flow soldered after being populated. In a perfect environment this works well but if any dirt or if production rate is pushed it results in these type of faults.

Can you make a video on how to open the amp to get to the head unit. I need to replace my input jack on my dsl40cr version. Not sure what input jack to use. And the nut for the input is chrome not black plastic like on the dsl40c version. Please help

I just changed the motherboard on my Marshall tsl 100 to an issue 20. The flow soldering on the old board was very poor, but the new one is very good.

Nice video Mr. White

Nice video terry. KUDOS

Verry intersting video!

Looks like the solder joints on V2 look pretty iffy as well...

Can those cheap pots get cleaned w Deoxit? I have an valvestate 2000 AVT100 with those

i just picked up a 1 month amp like this.the damn thing is so fuzzy/buzzy on the gain channel,it sux!any idea on what to do with it aside from a heavy dose of .357 magnum?

How can I get that tube tester?

Glad to see the old snozaramus ungar made an appearance

Terry I have the same amp but it has a low wooshing(wind noise) sound when on but not playing anything, nothing changes it except minor changes to volume of woosh when messing with resonance and presence knobs, any ideas? Thanks!

My dsl40cr (the updated model of this amp) does not emit any sound whatsoever. Powers on ok. Changed pre amp and power tubes. Still nothing. When I turn up the master I hear a buzzing sound. Could a blown fuse have done this? (I'm a newbie to all this stuff)

All Hail the Almighty Snozzeramus Ungar! (Sorry, Terry - Too Funny). Love your "Work Smart, not Hard" approach.

Hey Terry, what do you think about using a ground runner there?

Look like this one was a tuff one... Those pcb design.. I ain't a fan of those.. Thumbs up for your work and efforts on this Terry!

You are a genius

Great video but it seems like a lug on both sides and repurpose one of the screw/nuts already available on the chassis would have been a lot cleaner ground. Cheers

Very nice video! I'm having a problem with the same amp, but mine is that it intermittently cuts out. I have not found a pattern to the fault, but I have isolated to the amp with nothing else plugged in. Changing channels and cycling the standby have no effect, but the sound comes back instantly when I cycle the power switch. Any clues?

Why not just run a wire with a terminal ring on each end to your new screw and the nut on the chassis just below it? The effect would be the same.

Could you desolder the tubes and put sockets in their place? If you could, it would make it a lot easier if there was another tube failure in the future.

Great Job... Thank you

Hey I have a Marshall DSL40c and everything works but on the gain channel I have no gain? I get sound but it's at maybe quarter vol when vol is cranked. Any ideas?

Number one problem in tube amps is vibration that will loose ground screws and nuts thus it was a good idea to solder in the ground wire. This way you know you have 100% ground.

Marshall have admitted the issue was with the gyrator circuit. All Dsl's manufatured within the past 2 years are trouble free.

I love this.

So, the preamp is now grounded via the metal standoff and a ground wire - doesn't that risk a ground loop?

I'm incredibly ignorant to internal workings of amps electronics in general but that was a highly interesting and informative vid nonetheless!

Anyone have any tips regarding erratic Reverb?

Broken screws try a left hand drill bit. A lot of times the bit will catch and unscrew the broken piece.

R1/R2: Those weren't bad solder connections. Had you looked at the bottom, you would find them fully soldered. The holes are throughplated, so if any components had traces on the top side, there would still be a proper connection. If there aren't any top traces, adding solder only needlesly exposes the traces, throughplating and components to excess heat which can damage them. So always look first if the top side even has a trace leading to them.

00:56 - "The preamp tubes are all directly soldered in" . That would be interesting :) I've watched many guitar amp repair videos and have noticed very FEW tube failures vs capacitor failures! I wonder if Fender et al had to do this all over again, they would simply solder the tubes directly to the board and socket the electrolytics? :)

Watched the video earlier today and wondered if you (D Labs) or anyone here could possibly help. I got mine in January new and within a week, no sound. I was in the middle of playing one day, and all the sudden there was a little "bip" sound followed by silence. I've been sitting on the amp contemplating repairing the amp or sending it back. I thought perhaps it was a blown speaker, and I ran it into a 16 ohm cab, and no sound. All the tubes glow, though that doesn't always mean the tubes are working. When I turn the amp on, everything lights up. The footswitch changes the channels, and when I disconnect the footswitch, I can change the channels and the lights work. I tried my cable through the return of the effects loop, and there's no sound coming out. So I'm wondering if it's something simple as a bad tube or multiple tubes? Thank you anyone that can possibly help out!

Wouldn't it be better to tie that runner to a screw washer terminal? this way, the circuit board could be removed without having to de-solder the runner.

I have a DSL40C and it sounds great on the clean/crunch channel, to run pedals into. But, it started, just once in a blue moon, losing all volume, on any channel. It would dork the next day, or later in the same day. No rhyme or reason, and it's been looked at by two different techs, that found nothing wrong with the amp. Cleaned the inputs, did the FX loop trick, which seemed to work once, but not second time. And this happened three times in 6 months of playing regularly, always returning to sounding fine. I've had it re-soldered, the tubes aren't bad, and I've read different theories, but no amp tech has been able to find the problem. Heard of this? Any opinions or suggestions.

Wonder why you didn't drill that screw out with the chassis on it's side - let gravity assist and drop all that swarf into the clear chassis area rather than all over the board..

Nice!

i have a vintage traynor reverb master (jtm45/bassmaster clone) someone just offered me a dsl 40 on trade.... and my God i am happy i saw this video. what a piece of garbage. flimsy design.... great channel by the way bro!

God I HATE Circus boards! (Nice one Young Tel!!)

Judging by the amount of scratches on the upper lip of the chassis it appears somebody tried to remove it from the cabinet with a spatula. Great diagnostics and repairs, Thanks for showing an old Marshall hater this video.

I need your help..

If you'll dm me, I'll send you some left hand drills, makes getting broken screws out super easy...

Im in jersey i wish i could bring my Blues jr amp for repair