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Thread: Shock from My amp!

  1. #1
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    Shock from My amp!

    Amp : Fender JazzMaster Ultralight (notorious)

    After keeping the amp on for a few minutes i get a shock! the earthing fails. If i connect an external earthing wire to the chasis, the shock stops.

    Upon opening and inspecting the amp, I see that no wires are lose. The earthing wire is screwed tight to the chasis.

    The problem keeps repeating on every turn on and its hard to play ballads with all this electricity.

    Can anyone point me in a helpful direction.

    MY INVESTIGATION:

    I see a bunch of safety X Y capacitors. Are the failing and causing the shock? Can anyone help try and identify them to help me replace.

    Click image for larger version. 

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    Regards,

    Jonathan

    PS I hope im descriptive enough.

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  2. #2
    Old Timer
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    Welcome to the place.

    The very first thing that I would test would be the plug/cord wire. If grounding the chassis with an external wire stops the shock, then there must be problem with the ground connection of the ac cord or the amp socket.

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    Supporting Member Jazz P Bass's Avatar
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    This amp utilizes a Switch Mode Power Supply.

    Be very careful in there!

    As there is no known schematic available for the power supply, the answer to your question "I see a bunch of safety X Y capacitors. Are the failing and causing the shock?" depends on how they are wired in the circuit.
    If one end is attached to the chassis ground, then yes, there is a shock potential if they are bad.
    I see that the ceramic caps are dual X1/Y2 rated.
    For Line to Line use or for Line to ground use.
    X capacitors are used Line to Line.
    If they fail, they do so in a shorted manner.
    Then the mains fuse blows.

    Y capacitors are used Line To Ground.
    They fail open.

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    Lifetime Member Enzo's Avatar
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    I agree with the above suggestion to check the power cord first. The internal ground connections in the cord could be intermittent. Is ther an IEC connector - ie the power cord comes off? That connector could be loose, cracked, broken solder.

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    Education is what you're left with after you have forgotten what you have learned.

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    Old Timer olddawg's Avatar
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    I agree as well. Do a continuity test between the chassis ground and the earth ground
    at the plug end. Also be aware that the outlet you are using may be floating even if it has a modern receptacle. I see this all of the time in older buildings.

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  6. #6
    Supporting Member Jazz P Bass's Avatar
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    Which does beg the question "Why is the OP getting a shock?"

    How is a voltage potential being developed between the amp & the guitar.

    Even ungrounded, there should not be any voltage on the chassis.

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    maybe wall plug wired backwards , hot neutral?
    other wise idk

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    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by Jazz P Bass View Post
    Which does beg the question "Why is the OP getting a shock?"

    How is a voltage potential being developed between the amp & the guitar.

    Even ungrounded, there should not be any voltage on the chassis.
    Maybe standing barefoot or in conductive/wet footwear on a concrete floor. Or outdoors on a lawn or wet deck. Those can get you a tingle or more from hands thru the feet. It's happened to me, feels weird. And it's worrisome wondering if the shock is gonna get worse. Good question!

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    Lifetime Member Enzo's Avatar
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    Yeah, I don't recall him saying he got a shock touching the amp, he was just "getting a shock." SO in my mind that means off the mic or the floor or other gear, or whatever.

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