DSL100 apparently stuck in mute. Got the correct schematic?

Discussion in 'The Workbench' started by Matthews Guitars, Nov 12, 2019.

  1. Matthews Guitars

    Matthews Guitars Well-Known Member

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    So a friend brought me two amps to fix today. One, a Mesa Dual Rectifier, turned out to need two new preamp tubes and a new input jack. And after that, I must admit, it sounds positively beastly. WAY better than the Triple Rectos I used to own. If they'd sounded that good I'd have kept them.

    But the other amp is a DSL100. And it appears to be stuck in mute. OT meters out 36 ohms to ground on one leg, 30 ohms to ground on the other leg, on the input (tube) side. Output side meters out at just a couple ohms on any tap. Seems OK. Screen, plate, and bias voltages are in typical ranges. All the tubes test OK. There's just no audio. Fuses are fine.

    If I could find the proper schematic for this amp I'd have it solved in minutes. Signal path tracing will reveal the problem.
     
  2. anitoli

    anitoli Well-Known Member

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  3. Matthews Guitars

    Matthews Guitars Well-Known Member

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    So the DSL100 and JCM2000 share the same schematic? Or close enough? Just asking to be sure. But thanks.
     
  4. Micky

    Micky Well-Known Member VIP Member

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    So is it a DSL100h or a JCM2000?
     
  5. Matthews Guitars

    Matthews Guitars Well-Known Member

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    I think I get it. JCM2000 is the series as JCM800 was the series back in the day. The model number is DSL100H.

    I suspect a bad JFET is the culprit. I have those in stock. I'll be doing the component level troubleshooting in the next day or two.

    This will require me to break out the oscilloscope. No better way to look at the signal and see where it stops.
     
  6. Micky

    Micky Well-Known Member VIP Member

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    DSL100H schematics are commonly available on the Internet

    It is very different than the JCM2000 series.
     
  7. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    Plug a guitar into the effects return, do you get any sound?
     
  8. Lance Chambers

    Lance Chambers Well-Known Member

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    :slap:
     
    Last edited: Nov 12, 2019
  9. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    What mute switch?
     
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  10. Matthews Guitars

    Matthews Guitars Well-Known Member

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    No go on going in through the effects loop. Absolutely the only sound I got out of the speakers was when using my meter to probe the voltages on the tubes, when touching the probes to the wires going to the output transformer. Just a little buzz on contact.

    No mute switch I can see on this amp.

    I have not yet found the CORRECT schematic for this model.
     
  11. ricksdisconnected

    ricksdisconnected Well-Known Member

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    compare them side by side when you figure this all out and tell us what ya think.
     
  12. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    Maybe Relay4 or TR1 acting up. They are driven by the microcontroller.

    Is the mute function part of switching?
     
  13. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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  14. Lance Chambers

    Lance Chambers Well-Known Member

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    Well hell.......I was thinking TSL output mute when I typed that.:facepalm:

    I owe y'all a beer.:cheers:
     
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  15. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    Are you able to take voltage readings? Do you have a DC voltmeter?
    (doing this the schematic doesn't matter)
     
  16. Matthews Guitars

    Matthews Guitars Well-Known Member

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    Yes. All tube voltages seem to be in normal ranges. All switch functions seem to work, relays click when buttons are pressed, and so on.
    But it's muted at all times. I think there's a mute relay that's being commanded to stay muted.

    The OT primary resistances are 30 and 35 ohms.

    Tomorrow I've got a road trip to make so I won't be able to do a thing with this amp tomorrow. The following day I can spend some time on it and even start doing signal tracing with my o-scope. I will find where the missing signal stops.
     
    Last edited: Nov 13, 2019
  17. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    The effects loop is before the "mute" relay so there will be no signal to the PI.

    The "mute" function works along with other functions. You cannot hear its relay by itself. You need to investigate Relay4 and its switch mechanism TR1.
     
  18. Matthews Guitars

    Matthews Guitars Well-Known Member

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    Thanks, will do when I get back.
     
  19. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    @Matthews Guitars
    When measuring the OT primaries the DCR is taken at each side of the center tap; like from one plate wire connection/primary tap to the actual center tap. Each side of a 100W like this should read more like 14-20 ohms.

    Anyone else measure a DSL100H from the last series?
     
  20. Matthews Guitars

    Matthews Guitars Well-Known Member

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    I measured from center tap to each leg where they connect to two power tubes each. One side measured 30 ohms from leg to center tap, the other, 35.

    That reading isn't high enough for me to suspect a damaged OT. And even if it was damaged, it should still allow some signal to get through,
    at high volume settings at least.
     

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