Terrible ground loop interference..

[vNa5h]

Guys there's a terrible hum like sound from the TV. As well as a horizontal line moving vertically.
Since I connected a pc with HDMI...
The sounds go away as soon as I disconnect cable from the set top box

So the setup is like...

Set top with coaxial cable and rca cable to TV

HDMI from pc connected to TV..

Also there's strange cracking sound when switching the lights on and off from my 5.1 speakers which is connected by rca to pc...

Any idea how to avoid this

 

[vNa5h]

Anything guys

100+ views .. No reply

 

[omishra]

It seems earth ground is leaked or improper. Check last element (PC) power supply SMPS for earth connection. Sometime it leaks into metal body which comes on contact with signal ground.

Isolate one by one. I assume it started with connection of PC, so you can suspect it.

 

[sidvee]

You may need something like this. Not sure if it is available in India but other options may be available.

Amazon.com: Viewsonics VSIS-EU Cable TV Ground Loop Isolator: Electronics

Cheers,
Sid

 

[omishra]

One simple way - try to connect either STB or PC from mains of other room through mains wire extension box.
It looks like ground loop through all ground wires,

STB <-> TV <-> PC <-> mains
^----------------------------^

 

[vNa5h]

One simple way - try to connect either STB or PC from mains of other room through mains wire extension box.
It looks like ground loop through all ground wires,

STB <-> TV <-> PC <-> mains
^----------------------------^

Tried that.. Doesnt improve...

Only removing the coaxial cable wire helps..

 

[omishra]

Tried that.. Doesnt improve...

Only removing the coaxial cable wire helps..

What about RCA wires at same time? connected or disconnected?

 

[vNa5h]

What about RCA wires at same time? connected or disconnected?

Connected....

 

[vNa5h]

Tried that.. Doesnt improve...

Only removing the coaxial cable wire helps..

Or removing pc plug while watching TV

One simple way - try to connect either STB or PC from mains of other room through mains wire extension box.
It looks like ground loop through all ground wires,

STB <-> TV <-> PC <-> mains
^----------------------------^

 

[omishra]

Thats means its earth ground coming from mains is culprit.

 

[jls001]

When the source of TV signal and the display are powered by different phases of power supply, there tends to be 50 Hz hum lines on the display. But this usually does not affect the sound, so I'm guessing yours is a different problem.

 

[Hiten]

vNa5h,
is coaxial cable of good quality ? Are there any power cable running parallel or near the coaxial cable ?

 

[omishra]

All this equipments are having SMPS, so IMO ground is only culprit. It is only common thing looping around. Isolating RF cable and its ground will help.

 

[vNa5h]

All this equipments are having SMPS, so IMO ground is only culprit. It is only common thing looping around. Isolating RF cable and its ground will help.

So how come that be done

 

[omishra]

let me get myself understand, you mean coaxial cable which takes STB channel output to TV. Correct? If yes then there are ground isolators for cable TV which are nothing but two 0.1UF caps inline to both centre and shield wires, one each.

 

[vNa5h]

let me get myself understand, you mean coaxial cable which takes STB channel output to TV. Correct? If yes then there are ground isolators for cable TV which are nothing but two 0.1UF caps inline to both centre and shield wires, one each.

No .. Coaxial to set op box...

Set op box is connected to TV by rca cable

 

[omishra]

No .. Coaxial to set op box...

Set op box is connected to TV by rca cable

You mean thick wire coming from Dish Antenna to STB?
If that is correct then all mains earth pin in your 3-pin adapters are non working or improper. Get it corrected if below thing does not work.
As a workaround - using thick diameter copper wire, connect outer shield or pin metal jacket of coaxial wire to RCA metal jacket or towards PC chassis.

 

[jls001]

See if you can try one more thing - check the path of the TV coax cable from outside your home to the set top box, and see if at any point the coax is running very close to a power line. If yes, try separating them permanently by at least 6 inches. And if possible, run power line and coax crossing each other and not parallel side by side.

 

[vNa5h]

Any more inputs guys...

Will a coaxial isolator help...
There is something like 75 ohm.. Lightening protector written on it

 

[vNa5h]

Anyone?....