High voltage reading on one side of DSL 100

Discussion in 'The Workbench' started by Gibby1976, Sep 15, 2020.

  1. Gibby1976

    Gibby1976 New Member

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    Hi there. I thought I would ask here regarding my issues before sending my head off to a technician.

    Stupidly, I switched on my DSL without being connected to my cab, this blew the main fuse.
    I replaced the fuse and decided to test the bias readings on the amp.

    From the left bias pin to the center, it is reading 75mv, but from the third pin to the center l, its reading 7v.

    I've swapped out all the valves, used different cabs, speaker cables and different output jacks but it remains the same.

    I have run a multimeter between pin 5 of the power valve sockets and the chassis, all four sockets are reading a steady -40.1v DC over prolonged periods. This does not change between standby being operational and non operational.

    I've removed the chassis from the case and had a thorough visual inspection with nothing looking burnt, bulging or any other visual signs of damage

    Its from this point where I'm not sure where to continue my process of elimination.

    Any help would be gratefully recieved.
     
  2. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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    r6 or r9...

    upload_2020-9-15_14-5-11.png
     
  3. Gibby1976

    Gibby1976 New Member

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    R6 = 5.5kohm
    R9 = 1.2ohm
     
  4. Gibby1976

    Gibby1976 New Member

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    No reading across c46.
     
  5. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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    R6 is toast...

    both should be 1w 1ohm
     
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  6. Gibby1976

    Gibby1976 New Member

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    Just looked that up, I shall get that swapped out and report back.

    Thanks for the speedy response.
     
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  7. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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    C46 usually blows up, if it goes...
     
  8. Gibby1976

    Gibby1976 New Member

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    Hopefully a simple fix then. Thank you
     
  9. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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    yeah, although, in my TSL, I put a 1 ohm 5w resistor in R6 & R9, so they wouldn't blow so easily. It's a common problem. I'm not a tech, but, that seems to be the #1 problem w/ JCM2000 amp's.

    Some say that I shouldn't have changed it, but I'm ok w/ it. If that resistor doesn't fail, a fuse should blow. For some reason, the resistor blows before the fuse...

    You can either replace the same value, or upgrade 3w-5w.

    If you upgrade, change both R6 & R9
     
  10. neikeel

    neikeel Well-Known Member

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    I would see if I could upgrade the bias pots at the same time.
    The key is to get 1% tolerance resistors. Get a bundle and, assuming your meter is up to it, measure them before you install them. I would use 2w flame proof metal oxides and ensure the rest of your fuses are the correct values (they are important if you are not using the cathode resistors as secondary fuses).
     
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  11. Gibby1976

    Gibby1976 New Member

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    All fixed thank you Dogs of doom.

    Got my valves tested and one of them had failed in the misshap.
     
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  12. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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    the tube may have taken out the resistor...

    glad you got it sorted out!
     

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