Dsl40c Problem

Discussion in 'The Workbench' started by Russell Lawyer, Jan 4, 2017.

  1. Russell Lawyer

    Russell Lawyer New Member

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    I recently picked up a used DSL40c for a great price, BUT...the first gig I took it to the Power tubes started to rattle and I couldn't use it; No big deal, it's a 2013 amp with original tubes so that was somewhat expected. So I replaced the PTs and re- biased. The next show I used it on, I noticed that when I first turned the amp on, the Clean/crunch channel volume control no longer worked. I could control the volume with the gain control only. The volume would increase slightly when maxed out but when turned down all the way, still very loud depending on the gain setting. After playing an hour or so, it started working normally and the volume control was fine. It also worked normally when I first brought the amp home and tried it. Fast forward to my next gig....same behavior....I tried swapping all of the preamp tubes with no luck, and now the volume no longer functions no matter how long the amp is on. The red channel works great; no issues. Any ideas?
     
  2. ampmadscientist

    ampmadscientist Well-Known Member

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    And welcome to the forum:cheers:
    schematic
    http://music-electronics-forum.com/t39446/
    Cracked solder connection on clean crunch volume control?
    Relay 2 is bad?
    Relay 3 is bad?
    Seems like you would need a technician to fix that.
     
  3. Reel Tape

    Reel Tape Member

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    You can check the volume pot, make sure it is working
    then check for cold solder joints.
    After that I would let a tech look at it.
    I know two guys that had that problem, it turned out PCB boards were bad, Marshall replaced the amp.
    Of course they bought them new, I wish you luck in finding something simple.
     
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  4. Russell Lawyer

    Russell Lawyer New Member

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    Thanks for the info. It appears to be heat related, I've since discovered. If I let the amp get warm enough (81-83 F on the front plate area around the vol control) I can get the control to start working by tapping the knob a little. Do think the pot itself could be affected by the heat in a positive way? I wonder if I can check the pot somehow while it's connected?
     
  5. MarshallDog

    MarshallDog Well-Known Member

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    If you need a new PCB it is about 400.00 bucks plus labor if not under warranty...another 200.00 and you have a new amp! Let us know how you make out and good luck!
     
  6. Reel Tape

    Reel Tape Member

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    If you have a multimeter yes you can check it, just make sure amp is unplugged.
    You can tap on it and it works, you might want to get some contact cleaner like DeoxiT
    and clean the pots first.
    As far as heat affecting it, could very well be but I cannot say for sure
    without having the amp in front of me.
     
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  7. Russell Lawyer

    Russell Lawyer New Member

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    Wow. There's no way I would sink another $400 into this amp. I only paid $250 for it, but it was working fine when I brought it home. The trouble started after I replaced the El34s and biased.
     
    Last edited: Jan 7, 2017
  8. Marshallmadness

    Marshallmadness Active Member

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    You might try replacing all the pre amp tubes and see what happens. I had a tsl602 once that lost a channel and it wouldn't work no matter what. Everyone on earth told me it had solder problems, board problems, etc. I put new pre amp tubes in it and never had another problem.

    The tsl602 used certain tubes or tube halves for certain channels and if one didn't work right or like the amp it gave that one channel or feature problems.
     
  9. Micky

    Micky Well-Known Member VIP Member

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    Sounds like a bad solder joint in the 1st stage of the preamp.
    Best to have a Tech trace the problem out...
     
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  10. Russell Lawyer

    Russell Lawyer New Member

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    That was the first thing I tried, actually. I figured since the power tubes bit the dust, the others wouldn't be far behind. But it didn't help. I can just barely touch the volume knob and it will start working (But only when the amp is completely warmed up 20-30 min. usually. That's the crazy part. Its as if the heat is expanding something inside the potentiometer to make contact.
     
  11. tmingle

    tmingle Member

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    I replaced all the pots in my DSL401 a few years back. They were about 3$ a piece.
    i cant imagine the pots for the 40C would be much more.
     
  12. Russell Lawyer

    Russell Lawyer New Member

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    Did the DSL401 have pcb mounted pots? I'm wondering if I would have to remove the whole board or if I could un-solder and replace it from the top.
     
  13. MarshallDog

    MarshallDog Well-Known Member

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    These pots are a direct mount to the board. You would need to take the PCB out and IMO cut the pot into pieces so you could carefully remove it from the PCB w/o damaging the eyelets. Between the post that mount the pot and the actual cuirct points there is like 4-6 solder points if I remember correctly and I just don't see how it would be possible to deal with that many solder points at the same time to get the pot off the PCB w/o PCB damage...
     
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  14. tmingle

    tmingle Member

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    "Did the DSL401 have pcb mounted pots?"

    Yes. I am fortunate to work at a facility with proper temp-controlled soldering equipment and a desoldering station. The 401 had Alps pots, which I was able to cross reference to Panasonics and purchase thru Mouser IIRC. I am not sure what is in my 40C yet. If you dont have proper soldering equipment I highly recommend paying a tech to replace the pots. Since the 40C is a budget amp with cheaper components, I would have them all replaced.
     
  15. Russell Lawyer

    Russell Lawyer New Member

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    I recently replaced the HP/LP switch on my OCD pedal. It was a PCB mounted DPDT switch. I used a plunger style solder-sucker to remove most of the old connections, then was able to wiggle it loose. This would probably work on the potentiometer too, right? I have a the Weller digital control soldering station, as well.
     
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  16. tmingle

    tmingle Member

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    That should work well. Get some solderwick as well. Do you have an old PC board from an old DVD player, radio etc to practice on?
     
  17. Russell Lawyer

    Russell Lawyer New Member

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    Well, I managed to replace the volume pot without destroying my PCB (although it was touch and go for a while, whew!) and I'm happy to say everything is working great! Thank you all for your help!!
     
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