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Old 01-27-2012, 02:26 AM   #1
DMHDMH
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HDMI Ports - VOLTAGE ??

Hi All -

Need some help if you don't mind.

Was having a DirectTV receiver issue. I could get a satellite signal on one TV but not another....as I moved the HDMI cable from the back of that TV with a 99% signal, over to the other TV, satellite signal dropped to zero. Odd.

So this lead me to call Direct TV. After some analysis we were doing, he took out his voltage meter.

On the back of my fairly new Samsung Smart TV, if we touch the voltage meter to the HDMI Input Ports on the TV, it registers 47 volts !! Is it normal for HDMI ports to register 47 volts ?? Every other TV we tried...even another TV like mine....the ports registered ZERO volts. Blue Ray, etc. all work fine on the TV....however my concern is if I use the TV, any attached equipment would get fried. Any thoughts on what might be the issue. I wasn't aware HDMI ports had/carried voltage. I have checked the outlet, no issues there.

Thanks!
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Old 01-27-2012, 07:10 AM   #2
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Originally Posted by DMHDMH View Post
Hi All -

Need some help if you don't mind.

Was having a DirectTV receiver issue. I could get a satellite signal on one TV but not another....as I moved the HDMI cable from the back of that TV with a 99% signal, over to the other TV, satellite signal dropped to zero. Odd.

So this lead me to call Direct TV. After some analysis we were doing, he took out his voltage meter.

On the back of my fairly new Samsung Smart TV, if we touch the voltage meter to the HDMI Input Ports on the TV, it registers 47 volts !! Is it normal for HDMI ports to register 47 volts ?? Every other TV we tried...even another TV like mine....the ports registered ZERO volts. Blue Ray, etc. all work fine on the TV....however my concern is if I use the TV, any attached equipment would get fried. Any thoughts on what might be the issue. I wasn't aware HDMI ports had/carried voltage. I have checked the outlet, no issues there.

Thanks!
Is that 47 Volts relative to ground? AC or DC? Does HDMI have an outer ground shell like USB, and is it between that and wall socket 3rd prong ground you're getting the reading?
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Old 01-27-2012, 07:30 AM   #3
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Is that 47 Volts relative to ground? AC or DC? Does HDMI have an outer ground shell like USB, and is it between that and wall socket 3rd prong ground you're getting the reading?
Additionally I'd start by looking at a bad ground or a hot/neu reversed in the area of the TV/ DirecTV unit for a wandering voltage like that.
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Old 01-27-2012, 08:00 AM   #4
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Additionally I'd start by looking at a bad ground or a hot/neu reversed in the area of the TV/ DirecTV unit for a wandering voltage like that.
Technically that would be a bad GROUNDING conductor or a HOT/GROUNDED CONDUCTOR reversal, as the average 120V wall socket doesn't have a "neutral".

It has a conductor with insulation which is white or natural gray, which is known as the "identified" conductor, and is called the "grounded" conductor. This is the wider of the two slots on a polarized receptacle. The narrower slot is the "HOT" wire, and the insulation is almost always black, and when it isn't, it's almost always red,but can be other colors except white, gray, or green. The hole on a 3 prong outlet is the "grounding" conductor", does not carry current in normal operation and is bare or covered with green insulation.

The white wire is only the neutral when in a circuit with two "hots", each 120V away from ground and 240V away from each other.

In either case, the white wire is connected to the building ground at the service entrance (meter base) and insulated from ground everywhere "downstream" from there.

The grounding conductor, also called the safety ground or equipment ground, is connected to building ground at the service entrance as well, and serves to "ground" metal switch boxes, receptacle boxes, junction boxes, metal fixtures, and "panel boards", which usually means circuit breaker boxes.

It's only supposed to carry current if something goes wrong, and it's supposed to provide a sufficently conductive path back to the building ground at the service entrance that it immediately trips a breaker or blows a fuse.

If you take the front off of a circuit breaker box and there are two "ground bars" in there, the one with the white wires attached will be insulated from the cabinet, and the one with the bare or green wires attached will be bonded to it.
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Old 01-27-2012, 11:31 AM   #5
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Is that 47 Volts relative to ground? AC or DC? Does HDMI have an outer ground shell like USB, and is it between that and wall socket 3rd prong ground you're getting the reading?
Sorry...I'm not an electrician..but let me try to explain more. At this point I just have the TV plugged into the wall. No other items connected at all.

1. I tested the electrical outlet with a plug in device, shows NORMAL. No grounding issues, polarity, etc.

2. With only the TV connected to the electrical outlet. I take the Voltage Meter, put the black probe into the 3rd hole on an electrical outlet, and then I touch the 4 HDMI ports on the back of my TV (one at a time) with the red probe...each registers 47 volts AC on the meter . I have tested this same scenario at two other friends houses who have the same TV, their HDMI ports register ZERO volts.

3. If I plug the HDMI cable into the back of the TV..and test the other end of the HDMI cable....it registers 47 volts AC. Why is there basically "power" coming through the HDMI cable???

I'm concerned with plugging any device to my TV via HDMI for fear that it will fry the HDMI board on the connected device. (Direct TV tech also had the same concern).

My Blue Ray player, Yamaha receiver, all work fine and display on the TV fine.....just don't like the fact that there is voltage coming from the HDMI ports. Those devices work now...but will they eventually get fried?
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Old 01-27-2012, 12:02 PM   #6
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Sorry...I'm not an electrician..but let me try to explain more. At this point I just have the TV plugged into the wall. No other items connected at all.

1. I tested the electrical outlet with a plug in device, shows NORMAL. No grounding issues, polarity, etc.

2. With only the TV connected to the electrical outlet. I take the Voltage Meter, put the black probe into the 3rd hole on an electrical outlet, and then I touch the 4 HDMI ports on the back of my TV (one at a time) with the red probe...each registers 47 volts AC on the meter . I have tested this same scenario at two other friends houses who have the same TV, their HDMI ports register ZERO volts.

3. If I plug the HDMI cable into the back of the TV..and test the other end of the HDMI cable....it registers 47 volts AC. Why is there basically "power" coming through the HDMI cable???

I'm concerned with plugging any device to my TV via HDMI for fear that it will fry the HDMI board on the connected device. (Direct TV tech also had the same concern).

My Blue Ray player, Yamaha receiver, all work fine and display on the TV fine.....just don't like the fact that there is voltage coming from the HDMI ports. Those devices work now...but will they eventually get fried?
Is this a digital meter, or if it's one of the old kind (moving needle), is, or was, it a very expensive one?

I'm trying to figure out the internal impedence, roughly.

Expensive analog version, semi-high, doesn't load the circuit much, digital, very high, almost no loading at all, cheap analog kind (like Radio Shack used to sell), fairly low internal impedence, fair amount of circuit loading, which sometimes can be what you want. It'll give you a better idea of the "real" voltage of a battery, for example.

Do you have it on an AC or DC setting?

Did you start off on a high voltage range and bring it down to something like 0-250V or 0-100V?

Okay, going by this

http://en.wikipedia.org/wiki/HDMI

I'm going to assume you mean touching, with the red lead, the metal shell thing which an HDMI plug slips inside of, the part you'd expect just by looking at it to be grounded?

Yeah, I don't like the sound of it either.

If the meter is set for AC Volts, set the range to at least 200, and try it with the red lead in the ground hole in the socket and the black lead touching the outer shell of the HDMI jacks.

If it's set on DC, do the same, but if it's not a digital, touch real quick to see if the needle tries to go "backwards".

What's the brand and model number of that TV?

Also, there should be an FCC ID number on the back somewhere.
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Old 01-27-2012, 12:44 PM   #7
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Thanks for the help.

I am using the AC 200 setting when doing the measurements...if you google Craftsman Non-Contact Voltage Detector ...it's red.

By touching....yes I'm referring to touching the red lead onto hte medal casing HDMI port ...first sticking the black prong into the 3rd prong on the wall outlet.

Also...same result if I touch the USB ports also.

Like I said...did this same exact test on same TV down the street....zero volts coming out. Is my TV not grounded somewhere inside the case ? I've used a circuit tester..and everything is coming back fine on the outlet.

Brand is a SAMSUNG SMART TV 55" LED 3D HDTV - UN55D7000LFXZA

I'm just trying to do some analysis before the SAMSUNG Warranty Tech gets here next week. He will turn the TV on and see everything is working fine. I don't want to be told that voltage on the HDMI is not a problem...especially when I can't reproduce the same problem on 2 other TV's. ...and then months down the road find out my Receiver and Blue Ray are fried (out of warranty).

47 volts the other day. Now today I run the same test.....its 28.6 volts on each port.
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Old 01-27-2012, 12:45 PM   #8
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Here is the link to the meter.
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Old 01-27-2012, 12:46 PM   #9
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Sears Craftsman
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Old 01-27-2012, 12:46 PM   #10
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www.craftsman.com/craftsman-digital-multimeter-with-manual-ranging-non-contact-voltage/p-03482312000P
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Old 01-27-2012, 01:23 PM   #11
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Thanks for the help.

I am using the AC 200 setting when doing the measurements...if you google Craftsman Non-Contact Voltage Detector ...it's red.

By touching....yes I'm referring to touching the red lead onto hte medal casing HDMI port ...first sticking the black prong into the 3rd prong on the wall outlet.

Also...same result if I touch the USB ports also.

Like I said...did this same exact test on same TV down the street....zero volts coming out. Is my TV not grounded somewhere inside the case ? I've used a circuit tester..and everything is coming back fine on the outlet.

Brand is a SAMSUNG SMART TV 55" LED 3D HDTV - UN55D7000LFXZA

I'm just trying to do some analysis before the SAMSUNG Warranty Tech gets here next week. He will turn the TV on and see everything is working fine. I don't want to be told that voltage on the HDMI is not a problem...especially when I can't reproduce the same problem on 2 other TV's. ...and then months down the road find out my Receiver and Blue Ray are fried (out of warranty).

47 volts the other day. Now today I run the same test.....its 28.6 volts on each port.
I'm not quite sure how that no contact thing works, but that implies an extremely high input impedence. Basically sounds like a static electricity field sensor. Even if that "static" electricity is changing direction at 60 cycles per second.

That means you can have a voltage reading, but whatever's causing it is capable of delivering almost no current whatsoever.

Kinda like touching a doorknob in winter gives you a shock, but it's not enough current to knock you down or stop your heart, there's a lot of tension between where the electrons are and where they want to be (that's voltage, or electro-motive force), but there aren't enough of them (that's potential current, which is how many pass a given point in a certain amount of time), and their path isn't conductive enough (the impedence is too high).

Pulling a phonograph record album out of the plastic inner sleeve can generate thousands of Volts of static charge (which glues dust down into the grooves), but there's not enough current-delivering ability for you to even feel it.

But still, those things ought to be at ground potential.

Voltage spikes don't always have to deliver lots of current to damage solid state components.

I went through all 300+ pages of the PDF of the owner's manual, and there wasn't a single picture of the back or the power cord or any of that stuff.

Does this have a 2 prong polarized plug to go in the wall socket or a 3 prong?

Is this happening with the cable company cable hooked up to the TV or no connection to anything except the AC wall socket?

Have you tried the meter between socket ground and the cable company cable inner conductor and outer sheild?

In other words, is it coming in on the cable ground?

If you've got an actual Samsung warranty tech coming out, and he says it's supposed to be that way, make him put in writing exactly what causes it, 'cause I gotta hear this one.

See what reading you get with that meter between wall socket ground and the larger of the two slits. Theoretically, there shouldn't be any

Also, put that meter on a high DC scale and see what you get, and if reversing the leads shows a reversal of indicated polarity.
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Old 01-27-2012, 01:44 PM   #12
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It is a 2 Prong Plug for this TV.

Man...let me really confuse you now. Here are some different tests that I just ran....

1. Went down to a buddy's house with identical TV...just 60" vs. 55. Zero Volts

2. TV completely unplugged from the wall outlet. Not a wire running into it. Registers 2.1 Volts when touching the HDMI ports on back of TV.

3. TV completely unplugged from the wall outlet. Plugged in an HDMI cable to the TV. Nothing is connected on the other end of the HDMI. HDMI ports on TV Registers 2.9 Volts. (up a bit)

4. TV completely unplugged from the wall outlet. Plugged in an HDMI cable to the TV, and then connected the other end to the Blue Ray player. HDMI ports on TV registered 28.9 Volts

What is up ??? #2 is just odd. #2, #3 and #4 I would expect to occur with the same test on the similiar TV.
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Old 01-27-2012, 02:47 PM   #13
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OK....so I'm almost ruling out the TV. Let me explain. (If I even have a problem at all).

So tell me this....because it looks like the culprit as to why I'm seeing the numbers I'm seeing....I tested the Blue Ray player......black lead into the ground on the outlet.....red touching the end of the HDMI cable coming out of the Blue Ray player.....I get a 50V AC reading on the metal HDMI pin.

And that makes sense why I'm getting the reading at the TV.....I think.

So why does the Blue Ray player throw 50V through the HDMI cable ? I could go test the same Blue Ray player at my friends house...but I would suspect I would get no reading since I did not get a reading at the TV when I tested it. (and his Blue Ray player was connected).

Am I just chasing something that is normal ?
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Old 01-27-2012, 05:36 PM   #14
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BD player must be the culprit. It's entirely possible the power supply in it has a defect that's putting voltage across the HDMI lines, which it should not be doing. Replace it.

But to be certain (beyond the BD player problem) you'd do well to hire an electrician to check your outlets and wiring. It's entirely possible you have some ground or other wiring issues there.

For your meter to show reading when nothing is connected makes me think there's something defective about it. Or you didn't actually have everything as disconnected as you think...
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Old 01-27-2012, 06:02 PM   #15
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Yes some devices put out 5VDC over the HDI cable for powering things. I never knew this until this week when I bought a three port HDMI switch. The instructions said it would be powered by most HDMI outputs but if a device didnt have it, that they would send a power supply free of charge. Turns out my TivoHD did supply the power needed when switched to it but my Comcast DVR didnt.
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Old 01-27-2012, 06:16 PM   #16
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Unitron, some of the info you are providing is only good in your part of the country. In my part things are different and other parts of the country are probably different from both of ours. In NJ every outlet in the past 40 years that is installed has three wires and they are named different than in your area. The black and sometimes red wire is the hot, which gets connected to the breaker. Then there is a white wire called a neutral that gets connected to the other blade in the outlet and connects to the ground bar in the main panel. I say main panel because here in NJ if the box is a sub panel the white wires have to be insolated from ground in the sub panel. Then there is the bare copper or green wire which is the ground. That connects to the semi round hole at the outlet and connects to the ground bar in the main or sub panel. So things seem to be the same but they call things by different names.
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Old 01-27-2012, 11:19 PM   #17
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Unitron, some of the info you are providing is only good in your part of the country. In my part things are different and other parts of the country are probably different from both of ours. In NJ every outlet in the past 40 years that is installed has three wires and they are named different than in your area. The black and sometimes red wire is the hot, which gets connected to the breaker. Then there is a white wire called a neutral that gets connected to the other blade in the outlet and connects to the ground bar in the main panel. I say main panel because here in NJ if the box is a sub panel the white wires have to be insolated from ground in the sub panel. Then there is the bare copper or green wire which is the ground. That connects to the semi round hole at the outlet and connects to the ground bar in the main or sub panel. So things seem to be the same but they call things by different names.
In all parts of the United States the National Electrical Code is considered the authority. It is incorporated in part or in whole into building code law almost everywhere.

Everybody informally calls the white wire the neutral, but in a 120V situation there's no such thing. All the current that flows through the "hot" wire to the load returns through the white wire, and if you come into contact with an uninsulated portion of it you become an alternate path to ground and the current divides according to the respective resistances or impedences of the white wire and your body.

It's bonded to ground at the service entrance, which may be the main panel, but the buss bar to which the white wires connect is insulated from the cabinet in any sub panel and there is a separate buss bar in said sub panel bonded to its cabinet, thus grounding it, to which all the green or bare wires are connected.
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Old 01-27-2012, 11:32 PM   #18
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Yes some devices put out 5VDC over the HDI cable for powering things. I never knew this until this week when I bought a three port HDMI switch. The instructions said it would be powered by most HDMI outputs but if a device didnt have it, that they would send a power supply free of charge. Turns out my TivoHD did supply the power needed when switched to it but my Comcast DVR didnt.
There is, on pin 18, a provision for +5V, respective to pin 17, but the outer shell should be at ground potential, and ordinarily you might expect it and pin 17 to be at the same potential.

However, in the case of the OP's television, which has a 2 prong plug, neither of the 2 wires in the AC cord should connect to any of the chassis metal. Even in switching power supplies there is an isolation transformer, or, more accurately, a transformer which performs the function of isolation in addition to its other function.

So, there's AC ground, and then there's DC ground, and one must be careful where and how they meet.
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Old 01-28-2012, 12:15 AM   #19
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OK....so I'm almost ruling out the TV. Let me explain. (If I even have a problem at all).

So tell me this....because it looks like the culprit as to why I'm seeing the numbers I'm seeing....I tested the Blue Ray player......black lead into the ground on the outlet.....red touching the end of the HDMI cable coming out of the Blue Ray player.....I get a 50V AC reading on the metal HDMI pin.

And that makes sense why I'm getting the reading at the TV.....I think.

So why does the Blue Ray player throw 50V through the HDMI cable ? I could go test the same Blue Ray player at my friends house...but I would suspect I would get no reading since I did not get a reading at the TV when I tested it. (and his Blue Ray player was connected).

Am I just chasing something that is normal ?
You may be chasing a bit of a phantom. Apparently you have a very high internal impedence measuring device, and we don't know how high its AC frequency limit is. What you're seeing may be AC Voltage, but not necessarily 60Hz AC Voltage.

If you plug an HDMI cable into the back of your TV and leave the other end "floating", you've created an antenna, and not only will the electro-magnetic field created by the electrical wires in your house be picked up, so will any radio and television signals passing through, including cell phone, wi-fi, et cetera, because these are also AC, just at a higher frequency than the wall socket's 60Hz.

How much of that shows up on an AC meter depends in part on how high in frequency you go before it becomes unresponsive, in other words, its bandwidth.

I still want you to unhook the cable company cable from the television and measure from wall socket 3rd prong to the outer shell of the cable connector end (the part that you turn to screw it onto the threaded jack on the back of the TV), and from 3rd prong to cable center conductor.

Get a friend to help you move that TV to another room and measure from 3rd prong to the HDMI shells without the TV plugged in to the wall socket (and without any kind of cable or antenna connected and no other devices connected to it), and then do the same thing with its power cord plugged into the wall socket.
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Old 01-28-2012, 10:13 AM   #20
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In all parts of the United States the National Electrical Code is considered the authority. It is incorporated in part or in whole into building code law almost everywhere.

Everybody informally calls the white wire the neutral, but in a 120V situation there's no such thing. All the current that flows through the "hot" wire to the load returns through the white wire, and if you come into contact with an uninsulated portion of it you become an alternate path to ground and the current divides according to the respective resistances or impedences of the white wire and your body.

It's bonded to ground at the service entrance, which may be the main panel, but the buss bar to which the white wires connect is insulated from the cabinet in any sub panel and there is a separate buss bar in said sub panel bonded to its cabinet, thus grounding it, to which all the green or bare wires are connected.
I get it, I get that folks know the exact terminology, but I managed to explain what to look for in one sentence, I see a lot more there that would stop anyone else from a simple wiring check, talk about information overload.

A simple wiring check and confirmation that they are correct from a safety aspect should be the first thing on the list.
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Old 01-31-2012, 08:49 AM   #21
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Samsung comes out tomorrow...I will let you know what he / she comes up with.
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Old 02-01-2012, 04:48 PM   #22
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OK All - Samsung stopped out. After we did some troubleshooting..made some phone calls.

Basically (sorry..not an electrician).....the newer TV's are coming out with power cords that are only 2 prong'd. So...what was happening is (and someone above may have eluded to)....I have my TV plugged into an outlet that apparently is on one circuit. The receiver, blue ray, etc. etc. was all connected to an outlet on a different circuit. Lending itself to an grounding loop (??) situation. When we plugged the cable box into the TV via HDMI, and plugged the TV into the same outlet....no voltage reading.

Does this make sense....or does my Samsung guy got it all wrong?
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Old 02-01-2012, 04:56 PM   #23
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OK All - Samsung stopped out. After we did some troubleshooting..made some phone calls.

Basically (sorry..not an electrician).....the newer TV's are coming out with power cords that are only 2 prong'd. So...what was happening is (and someone above may have eluded to)....I have my TV plugged into an outlet that apparently is on one circuit. The receiver, blue ray, etc. etc. was all connected to an outlet on a different circuit. Lending itself to an grounding loop (??) situation. When we plugged the cable box into the TV via HDMI, and plugged the TV into the same outlet....no voltage reading.

Does this make sense....or does my Samsung guy got it all wrong?
Did he happen to mention if that voltage would have been able to deliver any appreciable current, or that it wouldn't and that only because of your meter's high input impedence did it even show up?

Ground loops are famous gremlins, especially in audio setups of any complexity.


Did I mention that you should have all of that stuff on one or more Uninterruptable Power Supplies?
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Old 02-01-2012, 06:13 PM   #24
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Yes...he mentioned there is voltage there...but no current....and therefore no harm to the TV. If there was current....my TV would not have been working perfectly all this time.

Ah...you did mention the UPS....I should look into one of those.

Thanks all for responding...definitely a frustrating thing to try and debug. He said the Samsung moved away from the 3 prong plugs because the TV has a very robust surge protection built into them.
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Old 02-01-2012, 07:02 PM   #25
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Yes...he mentioned there is voltage there...but no current....and therefore no harm to the TV. If there was current....my TV would not have been working perfectly all this time.

Ah...you did mention the UPS....I should look into one of those.

Thanks all for responding...definitely a frustrating thing to try and debug. He said the Samsung moved away from the 3 prong plugs because the TV has a very robust surge protection built into them.
To be technically picky, not no current, but very, very little. As in not enough to worry about.

If there's voltage, then any conductive path means current, but if the internal resistance of the voltage source is very high, the current will be very low, which is why walking across a carpet and touching a doorknob will "bite" you, but it won't knock you to the floor and stop your heart. It's a lot of Volts (which is why it bites, or shocks), but the path from your shoe soles through the carpet through the wood to the doorknob isn't conductive enough to let much current flow.

Thanks for reporting back, glad to hear everything's okay. Put your lighter loads (TiVo, cable box,DVD player) etc.) on one UPS and your heavy drawing stuff (like the TV and stereo that are easier to shut down during a power outage) on another UPS. That way, you have a better chance of your TiVo continuing to run and record successfully during a power outage.
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Old 02-01-2012, 08:00 PM   #26
SNJpage1
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The poster said he touched the meter lead to the end of the HDMI cable. Is the lead touching just one of the pins or is it touching all of them at the same time? That can cause the strange readings depending on how many pins he is shorting across.
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Old 02-02-2012, 02:36 AM   #27
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Originally Posted by SNJpage1 View Post
The poster said he touched the meter lead to the end of the HDMI cable. Is the lead touching just one of the pins or is it touching all of them at the same time? That can cause the strange readings depending on how many pins he is shorting across.
I think he was measuring from building ground to the outer shell of the HDMI cable/port. I think he mentioned getting a reading even with the TV unplugged from the wall socket.

Of course once you plug in a cable to extend that shield out a few feet, you've created an antenna, so a high input impedence meter with a high enough frequency response is going to pick up all kinds of the results of electro-magnetic fields in the area.
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Old 08-08-2012, 04:11 PM   #28
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Just doing some research on this issue, and wondering if any one knows what the effects of this measured voltage would be on a common(non-voltage passing) splitter could be? I have come across this issue several times, and it seems now that tv manufactuers have gotten away from the three prong plug, I am coming across it more and more. Basically, I am in the CATV industry, and have found that this "foreign" voltage is seemingly following our coaxial cable as the path of least resistance to ground. We are regulated by the FCC that we must bond our facilities to the home's ground, and hopefully having the same potential. Just as I have read above, yes you may be reading 50Vac, but there is not enough current in most cases for you to get shocked. The only adverse effect I have been able find that I feel is being caused by this voltage is with our broadband cable modems.
EXAMPLE:
I might get a call that a customers modem keeps dropping offline. I get to the customer's premise, and see that the modem is indeed offline. I remove the coax from the back of the modem, and I have perfect RF levels. The modem should not be offline. I hook the coax back up to the modem, but it does not come back online. The coax is in most cases ran to a splitter in the customer's NID, so I trace the line back to that splitter, and check my RF levels on the output of the splitter. Same as before, they are well within specs. I hook the coax back to the output of the splitter, and head back to the modem, and it is now online. At this point I start taking voltage readings with my Simpson meter, at the splitter, from all coax lines in contact with that splitter coming from inside the home. I may find that one or several lines have some form of measurable voltage feeding back to that splitter. It seems that over a period of time, the voltage has "saturated" the splitter, which is made up internally of two dissimilar metals, causing a small amount of corrosion to form between the center conductor of the coax(copper), and the internal connection of the splitter(not copper), and by breaking the connection of the two, I may be breaking away the corrosion as well, thus when I hook the connection back up, my modem comes back online. Does this in any way shape or form make any sense to anyone, or am I completely off base with what I think may be causing this?
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Old 08-08-2012, 05:45 PM   #29
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Quote:
Originally Posted by djrhemi View Post
Just doing some research on this issue, and wondering if any one knows what the effects of this measured voltage would be on a common(non-voltage passing) splitter could be? I have come across this issue several times, and it seems now that tv manufactuers have gotten away from the three prong plug, I am coming across it more and more. Basically, I am in the CATV industry, and have found that this "foreign" voltage is seemingly following our coaxial cable as the path of least resistance to ground. We are regulated by the FCC that we must bond our facilities to the home's ground, and hopefully having the same potential. Just as I have read above, yes you may be reading 50Vac, but there is not enough current in most cases for you to get shocked. The only adverse effect I have been able find that I feel is being caused by this voltage is with our broadband cable modems.
EXAMPLE:
I might get a call that a customers modem keeps dropping offline. I get to the customer's premise, and see that the modem is indeed offline. I remove the coax from the back of the modem, and I have perfect RF levels. The modem should not be offline. I hook the coax back up to the modem, but it does not come back online. The coax is in most cases ran to a splitter in the customer's NID, so I trace the line back to that splitter, and check my RF levels on the output of the splitter. Same as before, they are well within specs. I hook the coax back to the output of the splitter, and head back to the modem, and it is now online. At this point I start taking voltage readings with my Simpson meter, at the splitter, from all coax lines in contact with that splitter coming from inside the home. I may find that one or several lines have some form of measurable voltage feeding back to that splitter. It seems that over a period of time, the voltage has "saturated" the splitter, which is made up internally of two dissimilar metals, causing a small amount of corrosion to form between the center conductor of the coax(copper), and the internal connection of the splitter(not copper), and by breaking the connection of the two, I may be breaking away the corrosion as well, thus when I hook the connection back up, my modem comes back online. Does this in any way shape or form make any sense to anyone, or am I completely off base with what I think may be causing this?
You may be right about galvanic series action inside the splitter, and a high-impedence voltage/current source, like one of those screwy HDMI jacks, probably isn't going to help it any.
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