DSL100 Reverb not working

Discussion in 'The Workbench' started by mikeskory, Aug 21, 2019.

  1. mikeskory

    mikeskory New Member

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    I've fixed a lot of things on this amp and it sounds good. The only thing left is the reverb. Checked the cable, tried another tank. The output side of the original tank reads about 200 ohms. The input side reads about 25 ohms. I obviously can see that I'm missing the +15 volts at both IC1 and IC2 on the little reverb board. I either have the wrong schematic or else have something plugged in wrong because the path is not making sense. It has to be simple at this point but I need help again.
     

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  2. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor. free Mars!
    Reverb has an isolated ground connection.
    IC 1 : Set meter for DC volts.
    Red probe to pin 4 of he IC1.
    Black Probe to pin 11 of IC 1.
    What is the DC voltage? should read about 30 volts DC.
    LM348.png Make sure you are reading the pins correctly. Note the notch in the IC case, which locates pin 1.
     
  3. mikeskory

    mikeskory New Member

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    Ok! I was reading from chassis ground to pins 4 & 11. I got -16 on pin 4, nothing on pin 11. The same with IC 2. -16v on pin 4 and nothing on pin 8. Also I had checked continuity from IC1 pin 11 to IC2 Pin8...it was good. So if we look at the voltage on the 3-pin Con 3 (plugs into the little reverb board) we'd get approx 30v across pins 2 & 3. Is that correct? And if I measured pins 3 & 1 we'd get +15 and across 3 & 2 we'd get -15. Let me know if that is correct.
     
  4. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor. free Mars!
    Measure across ZD1 and measure across ZD2.
    Should read 15 volts across each diode.
     
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  5. mikeskory

    mikeskory New Member

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    Thank you! I'm going into the shop for a while tomorrow so I'll reply again tomorrow. Really this was a great help.
     
  6. mikeskory

    mikeskory New Member

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    Good morning "ampmadscientist"! After looking at the reverb board in this particular unit I see there is no ZD1 or ZD2. The 3 pin power connector (con3) has 1 white and 2 blues on it. From white to blues I get -16 or +21. Across the blues is +36. After plugging in Conn 3 I get +17, -17 and 31v across the blues. Measuring IC1 across pins 4 & 11 like you said I get 15v (not 30V). Also on IC2 I get 15v across Pins 4 & 8. Marshall Reverb 2.jpg
     
    Last edited: Aug 22, 2019
  7. mikeskory

    mikeskory New Member

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    I'm back to describing the problem as a loss of +15v to IC1 & IC2. I'm seeing 15v where I should be seeing 30v across the ICs. Also I want to conform that I have this plugged in right. There are only 3 connectors. Cons 1,2 & 3. Still not sure they are plugged in right. I think Con 3 goes to Conn 4 on the jack board, Con 2 goes to Con 8 on the mixer board and Con 1 goes to Con 4 on the main board. I'll look for something that shows the connections. The schemo got me all fouled up
     
    Last edited: Aug 22, 2019
  8. mikeskory

    mikeskory New Member

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    I found this video from the Guitologist. Starting at 21:40 he goes through all the audio leads very clearly and slowly. I was able to write them down and see the connectors. I'll try this tomorrow at work.
     
  9. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    I am not sure Ampmadscientist is looking at the right DSL.

    Be specific about the model and date of your amplifier because there are too many DSL series and all are somewhat different.
     
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  10. mikeskory

    mikeskory New Member

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    Good idea. I was the one who posted that schematic and now I see it's not exactly right. Will get info on amp tomorrow.
     
  11. mikeskory

    mikeskory New Member

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    Front: JCM2000 Dual Super Lead Back M-1998-06-0620-B All my audio leads are right now and the amps plays well. Except for the reverb. Digging into that fresh now
     
  12. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    Yes you are referencing the right schematics. That would be a 1998 JCM2000 model DSL100. The first ones/series.

    You can reference these too.
    https://drtube.com/library/schematics/69-marshall-schemas#JCM2000-DSL

    And @ampmadscientist was checking out the REVERB driver stage. :yesway:
    :)
     
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  13. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    @mikeskory
    Your boards have some updates to them so reference some of the later schematics too.

    As for ZD1 and ZD2, @ampmadscientist was referencing the 15V ones in the LT power supply at bottom of schematic JCM2-62-xx, Rear Output PCB.
     
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  14. mikeskory

    mikeskory New Member

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    Yes thank you. I figured that out this afternoon. Once I was sure that the cables were connected right I found the +15v was also missing on ICs 1 & 2 on the rear PCB. Then I saw the zeners. One was shorted. I used an NTE 145A to replace it. Amp sounds great. I'll fire it up tomorrow again before I call the cust.
     
    Last edited: Aug 23, 2019
  15. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    Thank the scientist (@ampmadscientist) . He got you there first.
     
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  16. mikeskory

    mikeskory New Member

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    AND thank you to the @ampmadscientist! In this unit I replaced the 2) 330mf caps (swollen) and the bridge to get it going, then output trans because it was cutting out every 15 mins, then re-soldered the connections on the rear PCB all around the 8ohm/4ohm switch, fixed my polarity on the new trans secondary, replaced 2 of the EL34s as I tried to bias it, then lost tract of the 2-pin audio cables and lastly the ZD1.
     
  17. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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  18. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor. free Mars!
    Oh OK. Glad you got it working.
    (notes for others)
    ZD1 ZD2 is in the power supply.
    Go back there and make sure those 2 diodes are on.
    Measure Each diode should have 15 volts DC across the 2 diodes.
     
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