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HDMI cable buzzing with current from induction?

post #1 of 3
Thread Starter 
I am baffled as to how this could happen, but somehow I have introduced current in an HDMI cable through either induction or some other mishap with a component. Hopefully someone here may know what I'm doing or some tips on how to debug this problem.

Short summary: Bought an enclosed media cabinet. Cut holes in the back for 2 x 120 mm fans pulling air through the cabinet from a hole cut in the bottom of the cabinet. Long term goal was a device that would adjust fan speed based on temperature. First test was hooking up the fans to a variable DC power supply that plugs into an AC outlet to see what DC voltage would be required to keep the cabinet at an ambient temperature.

In the cabinet are three components: Verizon Fios HD DVR, Xbox 360, Samsung BluRay player. They are all connected with HDMI. All the wires come in through a hole cut near the bottom in the back of the cabinet and run behind the wall where the tv is mounted, a Samsung 46" LED TV. I had this setup for 3-4 weeks before installing the fans, so I can only assuming the fans caused this problem.

I turned the fans on, trying different speeds and left them on for a few hours to see how long and what speed was necessary to bring the temperature down inside the cabinet. Ran the 360 to really get the heat going inside for a while. So far so good, the fans were doing their job.

After about 3 hours I decided to watch some tv and realized that the port connected to the DVR had gone dark. The DVR was working and turned on. I could change channels. I should have video. My first thought was that the HDMI cable had pulled out of the back of the DVR, but when I tried to pull out the HDMI cable to reset it, I touched the tip and felt it tingling as a bit of current ran through my finger. It felt about that same as when you stick your tongue between the contacts on a 9V battery.

I plugged it back into the DVR and then tested the HDMI connection into the TV. When I pulled that connection out I got the same thing, tingly current running through my finger. At this point I unplugged them at both ends and turned off the fans. The current eventually dissipated.

At that point I tried to recreate the problem (with the wire disconnected at both ends) by turning the fans different speeds, moving the wires around, and plugging it in and out of the DVR to see if the TV end would create some current. I couldn't make it happen again.

So far, HDMI port #1 (which had been the TV port) still wasn't working. I waited a while until the cable was completely drained and plugged it into port #4. This time the picture was worked. So I tried the connection back in port #1, and to my relief the port was working again (I was worried the port was fried).

All of the wires in the back of the cabinet are funneled together as they exit the cabinet through the hole. This includes two power cables (one to the UPS and one to the TV) which also run right underneath the lower fan.

Could the lower fan actually be introducing current into the HDMI cables? Is there something else going on here I'm not considering?

I really don't even know the best way to test it without putting the components at risk. There doesn't seem to be much in the way of HDMI surge protectors, and the cables themselves are supposed to be shielded.

Has anyone ever heard of this happening or what could possibly be going on here?

Thanks ahead of time for any help.
post #2 of 3
You need to connect a voltmeter set to over 100 volts between the points you felt the tingle to see how much the voltage is present using both the AC and DC setting of the meter. These points are the metal (likely gold colored) on the end of the HDMI cable (not the pins in the cable) and the metal case of the DVR. If the DC voltage is small, less than a volt, then your are would likely see a large AC voltage. The current is very low or it wouldn't feel like a 9V battery. This is common when the equipment on either or both ends of the HDMI cable connection doesn't have 3 prong AC plugs. IMO it is unlikely that this is a cause of your problem with the DVR. The HDMI cable itself will use its shield as a ground connection between the devices and the low current AC shouldn't cause a problem.
post #3 of 3
Thread Starter 
I tried taking the voltage across the line and didn't come up with anything of significance. There was negligible DC voltage and 1V AC whether I had the fans cranked up or not.

I let it run for a while to see if any build-up would occur but never saw it increasing in any way.

Of course I'm not sure if it has to be plugged into the TV to actually make the problem occur, but of course worried if I do that then the port will go out. Either way, not sure what to check next except for simply separating all the power lines from the hdmi cables.
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