Dsl100 doa

Discussion in 'The Workbench' started by lshindel, Jan 14, 2021.

  1. lshindel

    lshindel New Member

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    Hi,
    I'm working on a 2017 dsl100h. Was working one second no sound the next. Opened it up and found a blown FS1 fuse which is coming off the standby switch. Ordered fuses and while I am waiting thought I would Check the power transformer. No shorts to ground and continuity between the windings. Would like to check the output Transformer but my schematic does not show color coding on the wires. My schematic shows the part number of TX Op 900 0 1. Number on a sticker on the Transformer is VT 1410. There are six leads coming out of the OT, a brown, Gray, and red which I think are the primary and a black, green, and violet which are going to the output board. I am getting a reading of around 65 ohms between the red and brown wires on the primary and 35 and 29 ohms between gray and red and gray and brown. Are these readings okay. The only thing I can get between all three wires on the output is continuity I cannot get an ohm reading from any of the wires on the output side. No shorts to ground from any of the six leads.
    Has anybody seen the dead amp problem before so that I might Fast Track This repair?
    Thanks in advance.
     
  2. Chris-in-LA

    Chris-in-LA Well-Known Member

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    In my limited experience I found that checking for continuity in the primary side can actually send enough current through the windings to make faint sounds through the speakers on a working OT.
     
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  3. lshindel

    lshindel New Member

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    0k, we'll give i f a try.
    Thanks
     
  4. lshindel

    lshindel New Member

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    Ok, I'll give it a try.
    Thanks
    BTW
    How do you like your mojotone 2204 clone?
     
  5. KraftyBob

    KraftyBob Well-Known Member

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    It appears the Gray is your center tap on the OT primary. In a well balanced OT each half to the center tap should be half of the total. yours is:
    Red to brown = 65
    Red to Gray = 35
    Brown to Gray = 29

    That's pretty close. I just repaired Tweaker 15 with a bad OT and my ohm readings were all over the place. I'd say yours looks good. If I remember correctly not getting an ohm reading between the secondary leads is normal.

    Check for continuity between the primary and secondary - there should be none. If there is your OT has a short.

    If you have a variac you can apply a low AC voltage (e.g. 5-10 volts) to the primary (brown and red) and on the secondary measure each lead to common to get the winding ratios but you'd need the data sheet from the OT to reference to see if they are correct. Although the ratios should go down as the impedance (speaker tap) goes up.

    It seems to me your OT is fine.

    When you get the new fuse disconnect all the secondaries from your PT. Power on the amp and if it blows a fuse again your PT is shorted. If not, the problem is not your PT.

    Bad tubes can blow fuses so you should check those.
     
  6. DonP

    DonP Active Member

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    Yes, it was an output tube.
     
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  7. Chris-in-LA

    Chris-in-LA Well-Known Member

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    It’s really nice but I put in a Merren OT. It sounds every bit as good as my stock 2204.
     
  8. lshindel

    lshindel New Member

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    Hello everyone,
    Sorry it's taking me awhile to get back with the reply to all the suggestions. I went through and did all that was suggested above and everything checks out okay. After I installed a new fuse and it did not blow upon power up I reinstalled the tubes and when I turn the stand by off I still did not get any sound so I went to adjust the volume knobs and saw lightning in a bottle on V8. Pulled all the tubes and retested and all tubes showed okay although there is a soot mark on the bottom insulator plate . Did not blow any fuses. Check the voltages on the PCB without tubes and all voltages check out okay except for the heater voltages on V1.
    So after trying to trace the circuit out I have a question. I'm getting continuity with pins 4 + 5 but have nothing on pin 9. Can somebody tell me where the circuit for pin 9 on V1 is? Diodes 12, 14, 16 and 17 check okay as do R108 and R110.
    The PCB has printed on it DSL 100 - 60 – 00 issue 1.
    Any help would be appreciated,
    Thank you Screenshot_20210124-210543_Xodo Docs.jpg
     
  9. Chris-in-LA

    Chris-in-LA Well-Known Member

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    Pin 9 is the heaters and that circuit is usually linked in most amps to the other tubes and the PT. You should have continuity from pin 9 of V1 to other pin 9’s. The arcing in V8 is a bigger problem, may be a burned socket that is letting current jump between pins or a bad tube. I don’t think that I would reuse that tube. A bad tube will also cause fuses to blow. If the V8 socket is burned you should probably replace it as well or risk destroying more tubes.
     
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  10. Gene Ballzz

    Gene Ballzz Well-Known Member

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    @lshindel
    Just to save you from chasing your tail at V1, I believe that on at least the DSL100 and DSL40 the heaters for V1 have actually been converted to DC. Set your meter to DCV and let us know what you see!

    Unfortunately, even though some schematic pages have been posted, the power supply page is the one that is missing!

    Please Let Us Know?
    Gene
     
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  11. KraftyBob

    KraftyBob Well-Known Member

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    +1 You beat me to it Gene :)

    I think the rationale for the heaters on V1 being DC was to minimize noise that the AC signal could potentially pick up.
     
  12. Max Gahne

    Max Gahne Member

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    I had a thought but then realised I'm not certain which DSL100 you have. Does your's use a pentode/triode switch or voltage selection for attenuation?
     
    Last edited: Jan 25, 2021 at 10:23 AM
  13. lshindel

    lshindel New Member

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    Hi Max,
    This unit uses the triode pentode switch. Switch was in the full power position.
     
  14. Max Gahne

    Max Gahne Member

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    Thanks, my thoughts were about the model with variable voltage. You might still check fuse FS2 which is for the bias supply though even if it's blown I think you'd have sound. I'm attaching a link to a BillM youtube vid on how to make an audio probe, part 2 is how to use it. You'll either need it or a scope to start tracing the signal from the input jack and on downstream to see where it stops.

    Make an Audio Test Probe.wmv - YouTube
     
  15. lshindel

    lshindel New Member

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  16. lshindel

    lshindel New Member

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    Hi Gene,
    You were right it was DC, all this time I'm staring at the 4 diodes and didn't recognize that they were rectifiers for that circuit so I got 17. 3 volts on Screenshot_20210125-222215_Samsung Notes.jpg pin five. See the enclosed chart with voltages for all sockets with no tubes and standby off. Do they seem right?
     

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