Loud hum from my AV receiver when HDMI/power cable not attached to pc

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mickrick

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Bit of a strange one this. I have my home cinema pc connected to my av receiver by hdmi cable from either my onboard graphics or my GTX 750 ti graphics card. But any time I disconnect the hdmi cable from the card, or remove the power cable from the pc, I get a loud hum through my speakers. Once I reconnect the cable(s) the hum disappears. I changed my PSU to a Corsair HX 650 Gold thinking my PSU might be to blame, but the problem persists. Now I'm worried that there may be a grounding problem with the motherboard, an Asus ROG Maximus VIII Gene.

The rest of my system is:

i7-6700K and 24gb ram and Gigabyte bluetooth/wifi combo card.
 
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It does sound like a grounding problem on the receiver side. Used to be really common but not so much with a home that has wiring up to code standards.

Is the receiver using an outlet with three contacts for each jack? If not, then you probably don't have a ground wire running to the outlet so attaching a ground wire to the screw will do nothing since it's not grounded. Even if it does have three prongs the ground wire could be missing and still un-grounded.

If your receiver has a two-prong plug then sometimes just flipping the plug around will fix ground loops but that may not be possible if the plug is polarized (one prong bigger than the other) which it should be for safety. If it IS polarized, or flipping it doesn't fix it...
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mickrick

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Yes, even when power and hdmi cables are disconnected at the pc as well. Which definitely sounds like the pc isn't to blame. But connect both power and hdmi cables back to the pc and the hum disappears, but only when both are connected.

 
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M1ckr1ck

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Sorry I thought I'd already replied to you. Don't know what happened.

My receiver has a phono stage with a ground pin. Should I connect to that? Where should I connect the other end of the ground wire to?

 
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mickrick

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There's a phono stage on the receiver for a turntable and there's a ground screw for that. Would that be a good place for the ground wire? And where would I ground it to?

 
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clarkjd

clarkjd

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That would be a good place to start. Run a ground wire from that to the screw that holds the outlet faceplate on.

 
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mickrick

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Are you sure about that? I've read somewhere else that the phono ground pin shouldn't be used as a ground point for the receiver, just for a turntable ground. I don't want to cause any lasting damage to the receiver.

 
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clarkjd

clarkjd

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You can ground the phono to the receiver, should be a lug close to the phono input on the receiver. Then you can ground the receiver to the faceplate screw.

 
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drea.drechsler

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It does sound like a grounding problem on the receiver side. Used to be really common but not so much with a home that has wiring up to code standards.

Is the receiver using an outlet with three contacts for each jack? If not, then you probably don't have a ground wire running to the outlet so attaching a ground wire to the screw will do nothing since it's not grounded. Even if it does have three prongs the ground wire could be missing and still un-grounded.

If your receiver has a two-prong plug then sometimes just flipping the plug around will fix ground loops but that may not be possible if the plug is polarized (one prong bigger than the other) which it should be for safety. If it IS polarized, or flipping it doesn't fix it, then something's wrong with the wiring of either your receiver or, more likely, house wiring at the outlet/circuit the receiver is using. If you're using an extension cable or outlet box they could have the mis-wire. It's far, far preferable to fix/replace those if you can.

If the outlet is in fact not grounded try attaching a ground wire to a copper water pipe if you can reach it. It should be grounded for safety.

On the receiver side, attach the ground wire to a chassis grounding screw (check your instruction manual) or case screw if there isn't one provided. Look for a screw with an electrical ground symbol adjacent to it (a triangle shape with one line sticking out on top, like an upside-down christmas tree) and use that; modern electronic devices frequently provide these.

Don't attempt to attach the ground wire to any of the audio connections. You've no idea, really, what miswires may exist inside the receiver or house wiring. There must be some somewhere or you'd not be having this ground-loop problem.

Good luck
 
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