Case voltage

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FestYboy
FestYboy Posts: 3,861
in Troubleshooting
Been having an issue with a new to me Onkyo... Warm up results in loud static from the CC or one of the left channels when in any multi channel mode. Random and it subsides after 20 min or so.

While checking connections, I bumped the case and felt a tingle like AC voltage. Put my DVOM to it and can see ~50v between case and earth. 36v between case and me...

This isn't right, and I can likely fix it, but I need somewhere to start looking (likely culprits).

Thoughts?
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  • FestYboy
    FestYboy Posts: 3,861
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    Maybe I have this in the wrong section?
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  • mhardy6647
    mhardy6647 Posts: 33,027
    edited February 2018
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    Or maybe we don't have a good answer :|

    My knee jerk would be to see whether there's a "death cap" capacitor installed between the mains in and the chassis -- but I have no idea whether that's done any more, or even allowed for UL listed equipment any more.

    In the old days, it was done and those caps were (and still are) designed to fail open so as not to put the AC mains voltage on the chassis -- but in this day & age I just don't know what's being done. In theory, I don't think it's needed with a polarized (or three-prong) AC plug.

    https://robrobinette.com/Death_Cap_and_Ground_Switch.htm

    Any way -- in the olden days (when we used to have to use flint tools to carve our own resistors out of charred mammoth bones, you know?) leakage to the chassis/front panel was usually cured by replacing that capacitor (or some other component tied to chassis ground).

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  • FestYboy
    FestYboy Posts: 3,861
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    Looks like I'll have to pull this out of the system and start probing (ahem). But first!, see if I can't hunt down a schematic.
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  • mhardy6647
    mhardy6647 Posts: 33,027
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    Or just pop the top and look at the AC inset and power supply -- all could become clear.

    PS we have a very modern table radio with some detectable AC tingle on the front panel :( I try not to think about it. :neutral:
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  • FestYboy
    FestYboy Posts: 3,861
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    Got a schematic. Will update once flu is gone, and AVR pulled.
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  • mhardy6647
    mhardy6647 Posts: 33,027
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    FestYboy wrote: »
    Got a schematic. Will update once flu is gone, and AVR pulled.

    Not sure about your priorities there ;)

    Seriously, take care of yourself; don't become a statistic! :(
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