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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
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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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  3. #3
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    Thank you Bill.

    I checked the power chord terminals with a multimter. All are okay with no leaks. Other appliances work fine

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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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  5. #5
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    Thank you Bill.
    I checked the power chord and the plug for leakage using a multimeter. It works fine.

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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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    Thank you bill. Great to be here. I’ve checked the power chord with a multimeter. There are no leakages.

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    All the capacitors are connected to the chassis ground via the circuit board. They are 2 types, 680 pf and 1500 pf safety caps. X1 400V and y2 250V.

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    I’ve checked the connector as well. No leakage. There’s no solder on it, uses those clip like thingies that fit real snug. Idk what they’re called.

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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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  11. #11
    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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  15. #15
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    I get a shock touching the amp or the guitar! Ive used a tester it goes live.

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    Supporting Member Steve A.'s Avatar
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    If chassis is properly grounded there should be no shock hazard. Check for voltage between amp chassis and 3 prongs of AC socket.
    There should be 120vac between chassis and hot (skinny flat prong in AC socket.)
    There should be 0vac between chassis and neutral (wider flat prong) and ground (round pin in AC socket.)

    Steve A.

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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.
    Aye, thae's the rrrriddle.
    And Enzo is on it as well. We don't have a lot of info.

    I homed in on the "after a few minutes" part. I'm wondering if there's an AC line MOV in there that has floated down to near the AC line peak and is starting to leak when it gets hot. Likewise, The OP could well be on it with suspecting the X and Y rated safety caps. Or any of several other places where AC line is insulated from secondary ground an is leaking.

    We'd need more info to make a better guess. How much shock, what conditions, multiple buildings, how long it takes for it to happen; hey, houw about a voltmeter sampling the "shock" for how big it is!

    @OP: Forgive me if I have underestimated your skills and experience, but your comments lead me to believe you don't have a lot of experience with AC mains circuits, or with switching power supplies. Maybe you do, and I just missed it.

    If so forgive me, but we hate to lose budding amp-fixers to dying by electrocution. I used to design switching power supplies for a living, and I hate to go poking around inside them. It may well be that some simple component is soft failing and a simple desolder/resolder would fix it. But unless you really have the skill and experience, a trip to a tech to fix it is much cheaper than a funeral.

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    Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

    Oh, wait! That sounds familiar, somehow.

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    There are quite a few SMPS supplies that will float the output at about 60v-80v with reference to mains earth - enough for some people to get a shock or tingle, and common with some ungrounded laptop supplies. Whenever I've encountered this with equipment provided with a chassis earth there's always been a fault present and sometimes this has been on the mains side external to the amp (bad extension lead, faulty cable, plug-top, step-up auto-transformer or even a house with an earth fault). My first check is to measure the voltage between the chassis and an independent (verified) mains earth connection such as a cold water pipe.

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  19. #19
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    Cannot reply to my own thread

    Dear admins i cant reply to my thread, shock from my amp!


    When i try to post i get a message saying that my messages have to be approved by an admin. But its been a week and I cant do anything.

    Sorry for making a new thread but i dont know who else to ask.


    Thanks and regards,

    Jonathan

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  20. #20
    Old Timer J M Fahey's Avatar
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    the earthing fails. If i connect an external earthing wire to the chasis, the shock stops.
    Then *clearly* you have a grounding problem.

    ***might*** be inside te amp, anything can fail, but I very much doubt it, doubly so coming from Lawyer-aware Fender Corporation.

    Caps are probably related to it but not faulty ... very often, for RF protection issues, there is one cap from Live to chassis, another from Neutral to chassis.

    IF chassis is properly grounded, both do their duty (shunting RF, HF, pulses, spikes) to ground and nobody´s the wiser.

    But if chassis is poorly or not grounded, both caps in series form a voltage divider, and if you have 120V mains, chassis will end at about 60V AC from ground

    Something like that was mentioned above and this is the reason.

    Are the caps broken or wrong?
    NO, they are doing their job ... it is Owner´s fault not providing proper Ground, so go and solve that first.

    Do not mess with he SMPS nor touch its caps.

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    Juan Manuel Fahey

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    Old Timer J M Fahey's Avatar
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    Hi Guys, looks like the OP can't get in, maybe the Software "built a Wall" and will later proceed to charge him
    Im a new member and i cant reply to any of the comments on the thread i have created about "shock from my amp". For every reply a message says i have to await moderation. But its been more than a week. I don't know whom to contact about it, can you help?
    Can somebody with due powers help him?
    Thanks.

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    Juan Manuel Fahey

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    Senior Member nosaj's Avatar
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    Quote Originally Posted by J M Fahey View Post
    Hi Guys, looks like the OP can't get in, maybe the Software "built a Wall" and will later proceed to charge him

    Can somebody with due powers help him?
    Thanks.
    maybe built in spam bot protection?
    nosaj

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  23. #23
    Lifetime Member Enzo's Avatar
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    I think someone has to turn off the newbie switch. If tboy isn't watching, maybe Steve?

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

  24. #24
    don't forget the joker g1's Avatar
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    Reporting myself to flag this post.

    Admin: Please see post #13

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    Quote Originally Posted by The Dude View Post
    But, I did learn something. There are protons, neutrons, electrons, ............ and morons.

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