Voltage on ground of coax

[jwilson1982]

Quick question. I rearranged my living room the other day unplugged the power to my tv and cable box. I unplugged the coax which the cable company installed the also put an in-line splitter in to split to my phone modem and cable box. I plugged the power to the cable box back in and left the tv unplugged. I was about to plug the coax back into the splitter and right as I was about to connect i felt about a 50-60v on the ground of the coax connector and I plugged it into the splitter and poof the cable box no longer worked and it blew my tv as well but I only had it hooked up to the cable box through HDMI. My question is does anyone know what would cause this and how did it backfeed all the way through my cable box and tv. The tv wasnt plugged into the receptacle but the cable box was. Also would the cable company be responsible for the tv. I also unplugged everything and touched the coax and felt nothing then tried it in the phone modem and it worked, what would cause this and how did it go away after blowing my tv and cable box?

 

[GoldDigger]

Quick question. I rearranged my living room the other day unplugged the power to my tv and cable box. I unplugged the coax which the cable company installed the also put an in-line splitter in to split to my phone modem and cable box. I plugged the power to the cable box back in and left the tv unplugged. I was about to plug the coax back into the splitter and right as I was about to connect i felt about a 50-60v on the ground of the coax connector and I plugged it into the splitter and poof the cable box no longer worked and it blew my tv as well but I only had it hooked up to the cable box through HDMI. My question is does anyone know what would cause this and how did it backfeed all the way through my cable box and tv. The tv wasnt plugged into the receptacle but the cable box was. Also would the cable company be responsible for the tv. I also unplugged everything and touched the coax and felt nothing then tried it in the phone modem and it worked, what would cause this and how did it go away after blowing my tv and cable box?

The main reason that it could blow your equipment was that the standard Type F connector allows you to (forces you to) connect the center conductor before connecting the ground. That means that a transformer or power supply isolated volt or two between center conductor and shield suddenly can become 50-60 volts between the signal wire and the ground on the TV or other electronic equipment.
As for how the voltage got there in the first place, stray voltages leading to differences in the potential of AC neutral and earth ground in different areas around the house come to mind.
Most common when POCO has got a high impedance neutral problem and/or there are problems with bonding and grounding in the house wiring.

For people with satellite TV, where DC power is supplied over the center conductor, using the wrong kind of splitter in the wrong place can also cause problems.

 

[hbiss]

Probably things you need to ask the cable company about. There are several reasons for what you describe- voltage on the coax coming from the street, improper ground or ground block on the side of your house, improperly wired receptacle that the TV and cable box plugs into as well as a defective cable box or TV that cause leakage. Also, since the TV was not plugged in I have a hard time understanding how it was damaged.

-Hal

 

[GoldDigger]

Also, since the TV was not plugged in I have a hard time understanding how it was damaged.

The TV probably had at least a ground connection somewhere, but even if it did not, capacitively coupled 60v AC can wreak havoc with an RF amplifier input without much trouble.

 

[hbiss]

No, not likely, especially considering the only connection to the TV was a HDMI cable from the cable box. He wasn't even using the coax input on the TV so the RF stages were irrelevant. Are you sure the TV was even damaged and it just didn't go back to default settings after it was powered down? This whole story sounds farfetched. I haven't heard anything about the cable company replacing the damaged box as they would have to and what they had to say, only your version.



-Hal

 

[jacobsond]

I dont know where your voltage on the coax came from but it is not uncommon for a voltage spike to come on the HDMI line and blow the main board on the TV.Ive seen it a few times in the TV repair business. I would be surprised if your cable company will admit fault.