Electrical problems, zapping/frying my equipment

Thomas Carstensen

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Aug 30, 1999
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I have been having a very strange and hard to pin down electrical issue with my various home theater equipment. I’ve blown up over the past months about 2-3 tivos, and my projector 2 times. What is happening is that at seemlingly random times when I got to connect up say the HDMI cable on my tivo or the component, or sometimes the satellite coax cables, it’s acting as if there is 120V live that I’m shorting out and frys whatever I’m trying to hookup. I cannot figure out or understand what is going on here.

At first I though that the satellite coax cable was crossing so ac power line in my wall or something, but I ran fresh new coax from my satellite not going through any walls. Here is some of the scenarios where something sparked or blew up:

Scenario 1: I have a NEW tivo plugged into the wall, the DVI output going to a plasma tv and I’m watching tv. I take my projector off the ceiling from downstairs and bring it up and plug it in and turn it on. I plug in the 3 plugs of a component cable into the projector, and when I go to plug the first rca jack of the component connector I get a big spark and I lose picture on my plasma. Rebooting the tv everything is fine this time.

Scenario 2: In my main entertainment rack I go to put back my tivo into the rack (I’ve done this tens and tens of times before). I plug in the HDMI cable to my projector 1st, then I go to start screwing in one of the satellite coax and ZAP SPARK SMELL… end result is the dish’s LNB is fried, the tivo sat inputs are fried, and my projector will come on but not display a signal. The projector was sent in for repair and there was a fried diode that was replaced.

Scenario 3: Bedroom TV is showing live tv off a tivo onto a old zenith tube tv. I just had gotten my plasma tv and so I plug it in, turn it on, and then attempt to connect an RCA video cable from the video in of the plasma, to the video out on the tivo.. as soon as I try to do that ZAP SPARK again. End result is the tivo is fried – won’t even turn on, AND the tivo DOWNSTARS from all this can no longer pick up a signal, AND my DOWNSTAIRS ceiling project will also no longer display any signal and 1 of 4 LNB’s fried. I was in a completely separate room from the other tivo and projector. The projector was on showing tv and right after the zap – I heard no tv downstairs.

Scenario 4: I go to plug in a serial cable (head phone jack) to my tivo. It’s already hooked up to a running pc. Tivo is on hooked to a tv showing it’s on. As soon as I try to plug the serial jack into the tivo it sparks and the jack is fused to the plug.

You can see here that I obviously have something wrong going on, I’ve just can’t figure out what it is cuz this kinda stuff doesn’t always happen. But I also cannot afford to keep blowing up equipment try to figure this out.

I’ve checked all the ac outlets with a 3 prong tester – all good. I’ve used a voltmeter trying to find any sort of high voltage and no luck.

If anyone has any ideas or suggestion I’d really appreciate hearing them. This is driving me crazy and my pocketbook crazy.
 

Wayne A. Pflughaupt

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Wow, pretty wild stuff. Can’t say as I’ve ever heard of anything quite like it.
Ya lost me there. How did you lose the picture on the plasma while you were plugging cables into the projector?

The common denominator seems to be the Tivo. Since it fried in one of the episodes, I guess that rules out the possibility that it’s leaking high voltage into places it shouldn’t be. That points me to the satellite dish. Maybe it’s some kind of static discharge, although I can’t say I’ve ever heard of that being a problem. Was it connected to the Tivo in all these instances? Do you have the dish grounded? Are the coax lines coming from it into the house grounded? Both the dish and feeds should be grounded to the house electrical stake.

Regards,
Wayne A. Pflughaupt
 

Thomas Carstensen

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Aug 30, 1999
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Well the coax used to be grounded but i'm running brand new coax runs that don't go through the house/walls to rule out anything going on in the walls. And i don't believe my dish is grounded so that may be a place to start.

I have/had 3 tivos -- so i tried it again with a grand new tivo and i could tell it was going to spark again that one time.

Believe me if baffles the crap outta me how i could be plugging in my rca video in plasma connector and it zaps my downstairs tivo and projector.
 

Leo Kerr

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I'm not inclined to discount the house electrical system. You've got stuff that's on different circuits, or at a minimum, different outlets. If one outlet is wired backward for "polarized" equipment, you may be causing big problems there.

I'd start dissecting pretty much all outlets involved, making sure that the black wire goes to the correct blade; the white wire goes to the correct blade, and that the green wire goes to the correct screw. While you're at it, also take a good look at the outlet itself, and if it looks like it might have gotten hot, you may want to start replacing some of the outlets themselves.

I'm not sure the best way to do this, but you might also try and see if there's some way to measure potential across multiple outlets - if there's a major grounding issue somewhere, you may be developing 120VAC across the so-called grounds from two different outlets. (I've seen that happen before; not a pretty sight.)

But yes, as you've noticed, you've got serious problems somewhere, and I'd be inclined to disconnect everything until I figured out what they were. Unfortunately, it's probably not the easiest thing in the world to diagnose - a conventional light bulb won't tell you.

And I'm not electrician enough to tell you how to go about trying to measure across multiple outlets on different circuits without frying yourself. So, as an added measure, when you start pulling outlets apart, make sure the breaker is off, just in case you have a black wire touching something that it shouldn't.

You may want to consider installing ground-fault-circuit-interupters, either ni the breaker box or in the first outlet on each circuit - they're not just good in the bathrooms.

Leo
 

DBeistel

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To check the outlets for reverse polarity use a DVM. check left slot to ground there should be 0 vac and then the right slot to ground there should be 120vac. All outlets should have 120 to ground in the right slot.
 

Wayne A. Pflughaupt

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Wow, can't say I've ever come across that – and happy for it!


An easy to check voltage across grounds between two outlets would be to run grounded extension cords from both, so that you can access the female ends. Then you can check for voltage by putting the meter’s probes into the two ground holes.

Regards,
Wayne A. Pflughaupt
 

Thomas Carstensen

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Thanks for all the advice. First -- i have one of those plug checker things and all my outlets throughout the house are wired correctly. I also have thought of the cross-outlet different-circuit issue regarding possible ground potential, but i didn't know of a way to test that. I also thought i might just go ahead and get a electrician in and give my electrical system a through looking over. I do have a degree in Electrical Engineering but this kinda stuff beyond the basics is not my forte.

As for GFI i've already purchased a couple more of these and will install them in the outlets i use for all my components this weekend.

Now that i think about it this problem only happens when i'm plugging in equipment from a different outlet. In my bedroom i run the plasma/etc all off of one outlet (powerstrip). When i've had the sparking issue in the bedroom (1st testing the plasma tv, the serial cable via pc, and the projector a couple days back) those were all plugged into a whole other outlets on the other side of my bedroom.

I'll try measuring between grounds and see if i see anything


Thanks again for everyones ideas!!
 

Thomas Carstensen

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This just popped into my head...

Remember how i said i took my bedroom tivo several times and put it into the theater rack to use on the projector without incident while my repair unit was getting sent back!?? And i was baffled that when i went to put the repair unit in... ZAP? the difference that time was that when i put the repair unit in i had the bedroom tivo hooked up. Thus there is a common connection between the 2 (satellite) and they are both plugged into different circuits.

Also -- my brother says this about measuring between grounds:

> Measuring the potential across different grounds is easy - however, you
> could be 'modifying' the state one of the ground loops only when something
> is plugged in and active one a particular circuit - for example there was a
> problem in one of the outlets, which only shorted a ground to a hot wire
> when something was plugged in.
 

Allan Jayne

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You could try this:

Disconnect all audio and video cables including HDMI.

Plug in all the equipment to wall outlets.

Turn on each piece of equipment.

Measure voltage from the shells and also the center pin connections of RCA and coax and BNC jacks to the power outlet ground.

Measure the voltage from all combinations of the various ground pins of the different outlets you are using. A long single conductor wire with alligator clips on the ends is a big help. A hint that has been found in many TV repair books: To avoid electric shock, use just one hand, putting your other hand in a pocket when making these connections and conducting all tests.

Measure the voltage from jack shell (just one) of each piece of equipment to jack shell of each other piece of equipment, all combinations.

No significant voltage should be measured in any of these places, otherwise you have either defective equipment or defective house wiring.

While there is still equipment made where the chassis is connected to one side of the line (one of the two flat plug blades), such equipment must have no exposed metal -- knobs, screws, heat sinks, jack shells, etc. other than trim that does not touch the chassis.
 

Leo Kerr

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Do make sure, however, that what ever you find out - whenever you find out - you let us know what was going on!
 

HareBall

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The problem with telling someone to check the left and right sides is that the outlets may be upside down to what you are seeing at your house. Some people put them in with the ground hole up and some put them with it down.
A better way to tell if you have them wired right is to look at them and check from ground (the center half circle shaped one) to the narrow slot. When you check here you should get ~120 volts. When you check from ground to the wider slot, you should get ~0 volts. If you look at back of the outlets, they should be wired with the black wire to the gold screw and the white wire to the silver screw. Ground, this can be either bare copper or green, should go to the green screw.
 

Thomas Carstensen

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thanks for the replies.. i'm going to have an electrician come out soon. i'm still trying to find what the problem is.

Could this kind of thing happen if my dish is not grounded. Neither the dish nor the coax cable is grounded.

also,
w/ the circuit breaker off and using a continuity tester i get a connection from neutral to ground and none for hot to ground.

is this normal?
 

Leo Kerr

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Very often the neutral (generally the white wire) is tied to the ground in the breaker-box. If you get more than a fractional milliamp between hot and ground, it should trip a GFCI; that is a very bad thing.

Bad, that is, to have current leaking between hot and ground; good to have the GFI snap.

Leo
 

Thomas Carstensen

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Aug 30, 1999
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you will not believe what my problem electrically was. had an electrician out today, we spent 2 hours going through the wiring and all and during his testing he found a live coax cable, the one that connects all my tv's throughout the house. We tracked it down to my kitchen tv -- it was leaking voltage out onto the coax connector.

he said he's never seen that before and i would never of thought of anything like that happening. the tv works fine, but will now go to the dump.

2 hours and $150 -- well worth not frying anymore equipment.
 

Leo Kerr

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um, they aren't supposed to do that, are they? Any idea how much voltage and/or current it would dump out the input?

Leo
 

Thomas Carstensen

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So i wanted to run some tests myself on the voltage issue i have/had.. Got my voltmeter out and plugged the culprit tv in (tv off) and measured from the ground plug of an outlet to the outside coax threads and i got 60 VAC. I thought this verifies what the electrician saw, but then i decided to try the same measurement on my office tv -- same result. Then i went into the basement and pulled out the old zenith and measurement from pipe-ground to outside coax thread and i got the same 60 VAC.

I find this strange and now i'm more confused. The outside of the coax is chassis ground -- i don't see why i should ever get any ac voltage measurement across it.

thoughts?
 

chuckg

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This is very odd....are you saying that you had no antenna or cable connection, and the TV was plugged in but turned off?

What meter were you using? If it was digital, are you sure it said 60V and not 60mV? Those digital meters are mighty sensitive, and I have been fooled by them....

Was the TV plug a grounded type, or just a two-pronger? Are you sure the outlet was properly wired?


I think I'll test a few TVs, just for giggles.
 

Thomas Carstensen

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Aug 30, 1999
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Tv plugged in but turned off -- no cable or antenna connected. i'll double check that it was volts. tv plug a non-grounded type (tv is a 13" sony trinitron).
 

Glen B

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I tested one of my TVs at home and got a reading of 67 VAC between the coax threads and outlet ground but the current was an extremely low and insignificant .078mV, which is what I suspected would be the case.
 

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