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Old 03-02-2019, 05:08 AM   #1
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Hum Hum Hum!

I have a hardware problem! I recently upgraded to a new computer, typical Tower format, probably 3/4 size of normal. Everything's fine except when I try and record a video. I get like a mains hum, you can hear it in this YouTube clip here:- https://youtu.be/kxT8CfL3MSI?t=98

Now the reason the hum suddenly starts at that time index in the video is because I lift my hand off the PC! To stop the hum I place my hand on the PC. Unfortunately when I need to type something on the keyboard I need both hands! So I lift my hand off the PC and then I get that bloody hum!

I'm using the same USB headset I used with my old PC, and I never had any difficulties on that. I've tried Earthing the PC to the adjacent brick wall by lodging a spoon against the wall and the PC. This had no effect.

The only thing that seems to work is by placing my hand on it. However it is intermittent! Some days it does it and some days it don't. I suspect by touching it I'm causing some sort of capacitance because I'm not directly touching the metal just the paint work.

Just wondered if anybody had any idea what I could try next!

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Old 03-02-2019, 08:53 AM   #2
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Re: Hum Hum Hum!

Try earthing the tower.?
By you touching it, you will likely be earthing it.?

I would have hoped it was earthed via the mains though.?
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Old 03-02-2019, 10:56 AM   #3
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Re: Hum Hum Hum!

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I would have hoped it was earthed via the mains though.?
That's a good point ! That's an assumption I would make too, however seeing as you mention it, I will check the cables and make sure they do actually have an earth in them.

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Old 03-02-2019, 11:22 AM   #4
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Re: Hum Hum Hum!

Code:
 
Unfortunately when I need to type something on the keyboard I need both hands!
sock off, foot on casing?
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Old 03-02-2019, 11:50 AM   #5
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Re: Hum Hum Hum!

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Originally Posted by CJ_London View Post
sock off, foot on casing?
Might be worth a try!

I've got some of those ferric rings you put around electric cables somewhere, but I can't find the damn things!
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Old 03-02-2019, 10:59 PM   #6
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Re: Hum Hum Hum!

I'd double check to make sure how each connection is set. The "Hmm" sounds like an issue I get when my headset jack isn't properly seated. Improper connection some where could be causing a slight amount of interference.

I haven't heard of it with a USB device though, going by the sound.

if it IS a grounding issue, you may need to ground yourself/headset. If YOU are causing the issue, it may be that when you touch your case, you ground. Otherwise you could be causing the interference. As a simple check, try making sure you have skin to case connectivity when using the headset.

I would also look to current humidity / when last your furnace was running in case your getting an atmospheric charge.

Last edited by Mark_; 03-02-2019 at 11:00 PM. Reason: fingers can't seem to type what the brain asks them to...
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Old 03-02-2019, 11:55 PM   #7
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Re: Hum Hum Hum!

If you try CJ's idea, we are going to need pic and/or video. For the sake of science of course...

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Old 03-06-2019, 03:22 PM   #8
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Re: Hum Hum Hum!

Still waiting on that picture/video to see if your foot solved the issue...
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Old 03-06-2019, 06:15 PM   #9
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Re: Hum Hum Hum!

Are there any other mains powered peripherals connected?
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Old 03-06-2019, 06:18 PM   #10
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Re: Hum Hum Hum!

Could it be that the cover of the PC is not properly connected internally to the chassis and the light pressure from your hand is making it connect? Try applying a light pressure with something other than you hand.
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Old 03-07-2019, 01:47 AM   #11
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Re: Hum Hum Hum!

To elaborate on Galaxioms second suggestion, if you have a multi meter, set to AC volts, measure from a bare metal part of the case (lid) to a known good earth point.

If you see a reading of more than a few volts then it's likely the case isn't earthed, or earthed properly.

Edit: I want to see that video as well...
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Old 03-07-2019, 06:56 AM   #12
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Re: Hum Hum Hum!

A "floating" ground can be a pain in the toches - literally, if the float amount is high enough.

When I was working my way through college, ungrounded or poorly grounded musical instruments OFTEN had this issue. Of course, back then, the two-prong plug was common-place for music amplifiers. Now, almost everything you can buy from a quality brand-name will have the three-prong plug with a positive ground. Further, the few modern items that still use two-prong plugs will have asymmetric plugs with one of the plugs being wider than the other. That "UL" sticker pretty much guarantees it.

If you have three-prong plugs and a multi-meter, you can do a quick CAREFUL test by comparing the ground socket to each of the other two sockets using the meter's AC Volts setting. In the USA, one of those leads will be "hot" and the other "not." But the one that isn't hot should be zero with respect to ground. If it is anything else, you have a ground fault somewhere.

If you have a simple power strip that you commonly use, start there and work backwards towards the wall to see where the ground fault originates. If the fault is in the wall socket you will need a licensed electrician to fix this. Or take off the wall socket plate and verify that all of the wires are connected to screw-type terminals on the socket. In the USA, that will be black, white, and green wires. You also need to know where your wiring enters the house and where the ground lead is attached to either a buried copper spike OR a metal part of the plumbing. Sticking a spoon in the wall won't work unless the spoon is touching the plumbing.

If you have a battery-based power conditioner connecting your PC to the wall, check THAT first of all - and if it shows up there but then the next leg (where the conditioner is plugged into the wall) does NOT show a ground fault, it is time to either replace the conditioner or exercise a warranty option.

You can also use the Multi-meter Ohms setting to verify good connection on the PC's power cable. If you've gone to the trouble of getting out the multi-meter, might just as well check everything.
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Old 03-07-2019, 08:30 AM   #13
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Re: Hum Hum Hum!

Also, when you look at the jack, does the jack appear that any of the metal ring is touching the case? That can cause feedback that might be correcting when you have pressure on the case. There are many possibilities here. Have you tried different peripherals? Do you have a picture of the jack?
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Old 03-07-2019, 09:05 AM   #14
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Re: Hum Hum Hum!

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Originally Posted by The_Doc_Man View Post
A "floating" ground can be a pain in the toches - literally, if the float amount is high enough.
I believe I need to refrain from asking what you've chosen for your seat...

Then again this is a good reason not to earth to your plumbing.
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Old 03-12-2019, 01:27 AM   #15
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Re: Hum Hum Hum!

Again thank you all for your comments, most helpful! And no, I'm not sat here with a naked foot touching the PC case, although it does gender some very strange interpretations! I've connected an old speaker wire between a lug on the PC for attaching some sort of locking mechanism and the radiator. The radiator end is clipped on with a pair of mole grips! Now I don't have any buzz! Only the buzz of success! Oh yes, and there is one other buzz. As I was preparing the end of the copper wire, I had attached one end to the PC, I was holding the other end ready to attach it to the radiator when I got the distinct tingle from it. In other words the PC case has some sort of voltage associated with it. So that appears to be what's causing the hum, now I need to work out whether it's a normal phenomenon or whether there's something wrong with the power supply.

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