Marshall lead 15 no output

Discussion in 'The Workbench' started by Shardik, Jul 14, 2020.

  1. Shardik

    Shardik New Member

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    I'm fixing a marshall lead 15 for a friend. It had a burned up resistor(r32) that I replaced but I couldn't find a schematic so I guess I winged it and put in a 10k 1/4 resistor there. Now it powers up but I have no output out of the speaker outs.... it has a headphone jack and a line out on the front panel I get output out of them but not the speaker outs. Any help would be appreciated.
     
  2. GIBSON67

    GIBSON67 Well-Known Member

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    What color bands did the burnt resistor have? You should be able to determine what value it was based on the color bands.
     
  3. Shardik

    Shardik New Member

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    It was completely burned off the resistor
     
  4. Micky

    Micky Well-Known Member VIP Member

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    What model number? Is it all SS?
     
  5. jmp45

    jmp45 Well-Known Member

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  6. Shardik

    Shardik New Member

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    It's a g15ms
     
  7. Shardik

    Shardik New Member

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    Yes it's all ss
     
  8. Ken Underwood

    Ken Underwood Well-Known Member VIP Member

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    Never try to repair an amp if you dont know the basics and to try to do it for someone else is totally crazy.
    You are doing your mate no favours
     
  9. Shardik

    Shardik New Member

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    I'm trying to learn more about amp repair this is an amp that a friend had lying around that he said I could try to fix. I'm just here for advice on where to be looking and gain some knowledge.
     
  10. Matthews Guitars

    Matthews Guitars Well-Known Member

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    A burned resistor always mean that it was connected to something that drew too much current. Without knowing the circuit or seeing the schematic I would be unable to make a more positive diagnosis but I'm going to BET that the burned resistor is just a symptom of destroyed output transistors.

    So, new resistors of the right value isn't going to fix it. Replacing the damaged transistors and the current limiting resistors will probably fix the amp.

    You can start there.

    You may want to reference the schematics for a Lead 12 or a Lead 20 as a guide. They won't be exact but the Lead 12, 15, and 20 all share some basic similarities.
     
  11. Shardik

    Shardik New Member

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    Thank you
     
  12. Shardik

    Shardik New Member

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    So I'm looking at the transistors they say jcr4558DD and below that it has d128d is that a production code? I can find jcr4558dds listed but they all have different numbers on the bottom. Just want to make sure I order the right thing.
     
  13. jmp45

    jmp45 Well-Known Member

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  14. Shardik

    Shardik New Member

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    It only has three of those transistors I might just replace all three and see if that does it
     
  15. Christianw123

    Christianw123 New Member

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    Hi, I have exactly same problem on the same same amp which I picked up at charity shop today for peanuts. Wondering if a simple R32 resistor replacement was Enough to fix you problem? Or was there other issues? I have power but zero output and burned out R32.
     

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  16. Shardik

    Shardik New Member

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    I am waiting on my order of the output transistors, I'm gonna replace all three but I'm gonna do it one at a time. I'll let you know what I find out.
     
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  17. Shardik

    Shardik New Member

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    So I have replaced all three of the diodes.... and nothing for the speakers outputs. And I realized the reverb does not work either. I dont know if it worked before or not to be honest. The headphone out and the line out work. If I run the line out to a cab it is actually pretty good sounding amp! Any other suggestions?
     

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