Hum in subwoofer/ receiver that varies with volume

[hybridauth_Facebook_10154896652913676]

Hello,

I own a 5.1 home cinema system with an annoying hum in the subwoofer which is also the receiver. The hum can be heard as well when no devices are connected. On standby and volume 0 it is silent though. The hum noise volume depends on the volume I set on the system, i.e. at volume 63 it is nearly gone and increasing or decreasing volume from that point makes the hum louder. Also adjusting volume of the sub only effects the hum. It is least loud at +0 and loudest at max (+ or -15).

The hum first appeared after the sub/receiver lost power at once, like pulling the plug from the socket. It is a grounded system. Changing to a different socket on another group does not help.

Who knows what may be the problem and how to fix this? Thx alot!!

 

[Nathan]

It does sound like a grounding problem to me - although I see that you have grounded it. One possibility is that the ground connection point on inside of the sub has come lose. Might be worth unscrewing and having a look

 

[hybridauth_Facebook_10154896652913676]

Thanks for your reply Nathan.

On the sub/receiver you can see a ground logo and screw next to the grounded power input. If I try to tighten the screw it fails... Maybe this has gone lose on the inside indeed, will try to open and see, though I am no technician ☺ Do you think this failing screw can be the cause of the hum?

 

[hybridauth_Facebook_10154896652913676]

Ok, by now I opened the sub/receiver and found the following for the power circuit:

The plug has three pins (i.e. grounded). The upper pin (i.e. 12 o'clock position) connects to a yellow short cable on the inside. This yellow cable goes back to ground, i.e. it is attached to the metal frame and tightened by a srew and bolt. These failed/ were lose indeed in such a way that the bolt did not connect to the cable end. I tightened it, hoping to fix the hum, but no result.

The other to pins make, imho, a strange loop, but I am not a technician. The right pin (i.e. 2 o'clock position) connects to a red cable inside the sub that connects further. The left pin (i.e. 10 o'clock) connects to nothing though. Underneath these plug pins a fuse (glass tube) is located, which is intact. On the right side (4 o'clock) this connects inside the sub to the black wire. The left side (8 o'clock) connects to nothing. The spots/metal plates connecting the wires are all one pin, but only both nothings connect (i.e. double metal plate between 8 and 10 o'clock).

*Yellow

*Nothing1 * Red

* Nothing2 * Black

Is this correct, or should I switch Black and Nothing1 on the inside? I did not switch this since purchase. However I did have it serviced once without success at a local shop and maybe he changed it. Any suggestions are very much appreciated... Thx!

 

[hybridauth_Facebook_10154896652913676]

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