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Marshall DSL100H cutting out... What's causing this?

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  • Marshall DSL100H cutting out... What's causing this?

    Hello all,

    I have a Marshall DSL100H that cuts out after about 20 minutes of playing. The sound just drops. No crackle, boom or buzz. Just silence. The weird thing is the power light (the switch light) stays on. The fuse doesn't blow or anything. Just silence. The only way to get the sound back on is to switch power and standby off and then back on again. This is one very weird bug. Play for 15-20 minutes -> sound cuts out suddenly -> power amp off -> power amp on again -> sound comes back for another 15-20 minutes -> rinse and repeat. What gives?? Has this happened to anyone here before. Thanks


  • #2
    Well, it's something intermittent, probably triggered by temperature (or vibration).

    Many possible reasons.
    Start troubleshooting by measuring essential voltages while in failure mode.

    And please post schematic.
    - Own Opinions Only -

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    • #3
      Originally posted by Helmholtz View Post
      Well, it's something intermittent, probably triggered by temperature (or vibration).

      Many possible reasons.
      Start troubleshooting by measuring essential voltages while in failure mode.

      And please post schematic.
      Thanks. Will do.

      Comment


      • #4
        It could be as simple as a tube that dies after warmup. I might try swapping tubes to see if that takes care of the problem. You could start by seeing if the preamp out will still drive another amp when the amp dies. That would at least tell you if the problem is preamp or power amp. Do the filaments still light when there is no sound?
        "Yeah, well, you know, that's just, like, your opinion, man."

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        • #5
          Please do not forget the FX loop.
          If you are not using the jacks they may have become dirty.
          Run a jumper cord from Send to Return.

          Comment


          • #6
            The power switch is an illuminated type, so even with nothing connected it will light up when in the on position. You can plug your guitar into the FX return to see if the power amp is working. After trying the previous suggestions (which are the main cause of this type of problem), when it cuts out, try thumping the cabinet to see if it comes back on. These amps have plenty of connectors that link the different sections of the boards. They can also cut out due to the push-on connectors on the transformers being loose. Whenever I get these amps in for work I always check these. You could even have a bad fuseholder - especially the HT fuse.



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            • #7
              Ok.. so I played around with the amp and found if I use a patch cable on the effects loop I could get it to NOT cut out. Problem seems to be in the effects loop area. The weird thing is the bias adjustment. One side reads 65mV (sounds about right) but the other side reads 26 volts!! How is this even possible. I checked to make sure my voltmeter was set right. Used the 3 prong lug on the board to check each side. Any idea as to why the bias is so off on one side?? Thx

              PS: Just checked. The side read 26 volts is not connected to ground. So there is a short somewhere.
              Last edited by cluster; 01-14-2022, 06:48 PM.

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              • #8
                Clean send and return jack switching contacts.

                Sure you mean 26V not 26mV?

                Still not seeing a schematic.
                I don't consider it my "job" to find the appropriate schematic.
                Helmholtz
                Old Timer
                Last edited by Helmholtz; 01-14-2022, 06:53 PM.
                - Own Opinions Only -

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                • #9
                  Probably one of the 1R resistors in the power tube cathode circuits is open.
                  Schematic attached, but may not exactly match your revision of DSL100.
                  Attached Files
                  "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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                  • #10
                    Here is a picture of the board. The ground on the right is shorted. Therefore I get a weird 26volt reading on the bias. Both plates are at 475DCV. Bias at grids is about -36.
                    Attached Files
                    Last edited by cluster; 01-14-2022, 07:17 PM.

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                    • #11
                      found this schematic...
                      Attached Files

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                      • #12
                        Originally posted by g1 View Post
                        Probably one of the 1R resistors in the power tube cathode circuits is open.
                        Schematic attached, but may not exactly match your revision of DSL100.
                        thx. i'll check
                        Attached Files

                        Comment


                        • #13
                          Originally posted by g1 View Post
                          Probably one of the 1R resistors in the power tube cathode circuits is open.
                          Schematic attached, but may not exactly match your revision of DSL100.
                          You were right. Found the bad 1ohm resistor. Thx

                          Comment

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