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Old 07-09-2012, 09:23 AM   #1
Stormspace
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Shocking Current in THD

Yesterday I was moving my TiVo around and grabbed the case from the front, wrapping my fingers underneath on the right hand side and discovered that there is an active current running through the thing. In the past I had associated the current and subsequent shock to power running in the cable line itself, but when I touched the cable connectors I didn't feel anything. Several times I touched the TiVo while sliding it around to remove the HDMI cable and each time I touched a spot on the chassis that delivered the shock.

What gives? is this current coming in from the cable line, or do I have defective TiVo? It's done this from day one since I first discovered the shock when setting up cable cards and a tuning adapter a few years ago. This THD is unmodded so I know it doesn't have any loose parts I left laying around in it that might be causing it. Ideas? What are my options with TiVo? It's way out of warranty.
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Old 07-09-2012, 10:15 AM   #2
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SAFETY FIRST. If I were receiving a shock from a piece of ANY equipment, I would immediately pull the breaker and remove such equipment from operation. Do you have a meter you can use to see if its the TiVo or if it was just picking up stray current from something else (TV, UPS, your wiring)?
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Old 07-09-2012, 11:00 AM   #3
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Originally Posted by jrtroo View Post
SAFETY FIRST. If I were receiving a shock from a piece of ANY equipment, I would immediately pull the breaker and remove such equipment from operation. Do you have a meter you can use to see if its the TiVo or if it was just picking up stray current from something else (TV, UPS, your wiring)?
While I tend to agree with you. In this case it's been operating fine for years. I'm just a little annoyed that the shock it coming from the TiVo and not the cable line as I first thought. I'll try and get a meter on it tonight and post the results.
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Old 07-09-2012, 04:06 PM   #4
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Originally Posted by Stormspace View Post
Yesterday I was moving my TiVo around and grabbed the case from the front, wrapping my fingers underneath on the right hand side and discovered that there is an active current running through the thing. In the past I had associated the current and subsequent shock to power running in the cable line itself, but when I touched the cable connectors I didn't feel anything. Several times I touched the TiVo while sliding it around to remove the HDMI cable and each time I touched a spot on the chassis that delivered the shock.

What gives? is this current coming in from the cable line, or do I have defective TiVo? It's done this from day one since I first discovered the shock when setting up cable cards and a tuning adapter a few years ago. This THD is unmodded so I know it doesn't have any loose parts I left laying around in it that might be causing it. Ideas? What are my options with TiVo? It's way out of warranty.
If you are unsure of what you are doing around electricity, then I'd strongly suggest you find someone who is sure to check it out for you. A quick first test would be to hardwire the Tivo chassis to a grounded object (i.e.: one that uses a 3-pin AC plug and has its chassis connected to the ground pin of the plug). I keep some light cables with alligator clips on each end for such purposes. If the Tivo powers up ok and you still get shocks when moving it around then I'd say it's probably static electricity from the rubber feet on the Tivo rubbing over something like the laminate/vinyl surface of the furniture.

If its not static electricity (I about blew off one of my fingers from static electricity when hooking up an HDMI cable to my TV) then you should unplug the box, pull the cover, and check for shorts. Use your ohmmeter to check the ground from the power supply to make sure it has a good connection to the chassis. If that is good, then it is unlikely that any of the DC voltages from the power supply are shorted to the chassis. Why? Because the Tivo still works. You should also make sure that the two AC input connector pins are open to ground (i.e.: very high resistance).
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Old 07-09-2012, 04:24 PM   #5
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Originally Posted by lillevig View Post
If you are unsure of what you are doing around electricity, then I'd strongly suggest you find someone who is sure to check it out for you. A quick first test would be to hardwire the Tivo chassis to a grounded object (i.e.: one that uses a 3-pin AC plug and has its chassis connected to the ground pin of the plug). I keep some light cables with alligator clips on each end for such purposes. If the Tivo powers up ok and you still get shocks when moving it around then I'd say it's probably static electricity from the rubber feet on the Tivo rubbing over something like the laminate/vinyl surface of the furniture.

If its not static electricity (I about blew off one of my fingers from static electricity when hooking up an HDMI cable to my TV) then you should unplug the box, pull the cover, and check for shorts. Use your ohmmeter to check the ground from the power supply to make sure it has a good connection to the chassis. If that is good, then it is unlikely that any of the DC voltages from the power supply are shorted to the chassis. Why? Because the Tivo still works. You should also make sure that the two AC input connector pins are open to ground (i.e.: very high resistance).
If its static electricity its of the constant jolting type as it doesn't fade. I'm comfortable working around electrical components, but in this case I have a certified electrician buddy I'm going to have look at it just in case it's one of those grounding issues with the outlet. I'll keep you posted.
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Old 07-09-2012, 04:37 PM   #6
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Originally Posted by Stormspace View Post
Yesterday I was moving my TiVo around and grabbed the case from the front, wrapping my fingers underneath on the right hand side and discovered that there is an active current running through the thing. In the past I had associated the current and subsequent shock to power running in the cable line itself, but when I touched the cable connectors I didn't feel anything. Several times I touched the TiVo while sliding it around to remove the HDMI cable and each time I touched a spot on the chassis that delivered the shock.

What gives? is this current coming in from the cable line, or do I have defective TiVo? It's done this from day one since I first discovered the shock when setting up cable cards and a tuning adapter a few years ago. This THD is unmodded so I know it doesn't have any loose parts I left laying around in it that might be causing it. Ideas? What are my options with TiVo? It's way out of warranty.
On some model TiVos there seems to be about 60V AC on the power supply heat sink, although that should and is supposed to be isolated from the DC side ground, which is also the chassis.

You might want to get the cable ground checked relative to electrical outlet ground, in case it's not actually the TiVo that's got the problem, and then move on to diagnosing the TiVo, if necessary.
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Old 07-09-2012, 04:40 PM   #7
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If its static electricity its of the constant jolting type as it doesn't fade.
By definition, if it doesn't "fade" when shorted, then it is not static electricity. Static electricity is an incidental build up of electrical charges on a pair of surfaces separated by a non-conductive medium due usually to some contact phenomenon. Because the intervening medium is not very conductive, the voltages encountered can be very high, even exceedingly so, but the amount of charge stored is limited by the total surface area, which is usually fairly small. Unless there is something continuously rubbing together ( as is the case with a Van de Graf generator ), there is no way to replenish the charge as it dissipates, so a jolt from a statically charged surface can be pretty intense, but the charge disipates rapidly.

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Originally Posted by Stormspace View Post
I'm comfortable working around electrical components, but in this case I have a certified electrician buddy I'm going to have look at it just in case it's one of those grounding issues with the outlet. I'll keep you posted.
It shouldn't be.* The electrical input to the TiVo should be isolated from the case. The only thing electrically common with the case should be the shields of the CATV cable, the HDMI cable, any RCA cables, and of course the antenna input. Any one or all of them could have a potential compared to whatever else you were touching when you received the shock, which begs the question, "What else were you touching when you received the shock?" No matter what potential the TiVo (or anything else) has WRT Earth ground, touching it is not going to shock you unless you are also in contact with some other conductor of electricity at a differrent potential WRT Earth ground.

* - I say, "It shouldn't be". An incorrectly wired power outlet could most certainly cause a shock when you touch the TiVo, but it would continue to do so when the TiVo was unplugged from power, but still wired to the CATV line, the TV, etc. Note it is possible the TiVo could have its case grounded - intentionally or otherwise - to the "cold" power line or even unintentionally to the "hot" line, but it should not. A voltmeter will tell you if it is in a heartbeat.

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Old 07-09-2012, 04:44 PM   #8
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By definition, if it doesn't "fade" when shorted, then it is not static electricity. Static electricity is an incidental build up of electrical charges on a pair of surfaces separated by a non-conductive medium due usually to some contact phenomenon. Because the intervening medium is not very conductive, the voltages encountered can be very high, even exceedingly so, but the amount of charge stored is limited by the total surface area, which is usually fairly small. Unless there is something continuously rubbing together ( as is the case with a Van de Graf generator ), there is no way to replenish the charge as it dissipates, so a jolt from a statically charged surface can be pretty intense, but the charge disipates rapidly.


It shouldn't be. The electrical input to the TiVo should be isolated from the case. The only thing electrically common with the case should be the shields of the CATV cable, the HDMI cable, any RCA cables, and of course the antenna input.
So you are saying it could be current coming in over the coax?
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Old 07-09-2012, 04:49 PM   #9
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Could be current coming from another device or amplifier check by unplugging everything except the power then meter to the case of each connection.


While your at it check for proper wiring of all electrical outlets.
I am amazed by how many homes and business are wired backwards.
These testers are inexpensive and available from most hard ware stores.
A quick search found this 120 VAC Outlet Tester
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Old 07-09-2012, 04:53 PM   #10
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On some model TiVos there seems to be about 60V AC on the power supply heat sink, although that should and is supposed to be isolated from the DC side ground, which is also the chassis.
Which in turn is supposed to be isolated from both AC input lines.
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Old 07-09-2012, 04:56 PM   #11
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So you are saying it could be current coming in over the coax?
It could. It's not uncommon, expecially if the house ground is not good. Lots of CATV drops get fried every year by current from the house power when the Earth ground is not properly established. The cable can also carry an induced EMF from the overheard power lines if it is not properly grounded at the house.

It could also be from an improperly grounded TV or AVR.
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Old 07-09-2012, 05:06 PM   #12
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Old 07-09-2012, 05:08 PM   #13
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Could be current coming from another device or amplifier check by unplugging everything except the power then meter to the case of each connection.
Yep. Measure cable to TV, cable to AVR, cable to TiVo, and cable to house ground (the round, third port on American 125VAC receptacles). Then measure TV to AVR, TV to TiVo, etc. At some point, the measured voltage will be somethng other than very near zero.

Actually, before he does that, however, and even before he disconnects everything, he should measure between the TiVo and whatever else he was touching at the time. That voltage will tell us something about the nature of the short. If it is 120 +/- 10 VAC, then it strongly suggests a grounding / house power issue. Otherwise, an internal short somewhere is suggested, especially if it is DC.


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While your at it check for proper wiring of all electrical outlets.
I am amazed by how many homes and business are wired backwards.
Agreed. The most likely culprits are an incorrectly wired outlet ( or more than one ) and a bad house ground. There are quite a few other possibilities, bu those are by far the most common.
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Old 07-09-2012, 08:23 PM   #14
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Agreed. The most likely culprits are an incorrectly wired outlet ( or more than one ) and a bad house ground. There are quite a few other possibilities, bu those are by far the most common.
In our old house, we were getting shocked putting clothes in the washer. I found the issue to be a outlet wiring issue in another part of the house on the same circuit.

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