Haunted GFI in Bathroom

This is REALLY interesting:
Just had cable TV installed. From time to time, I'm getting terrible snow on all channels. While my son was in front of the TV yesterday, I walked into the bathroom and flipped on the light, and then turned it off a minute later. At that moment, the TV picture cleared up. About the light switch: It's mounted in the same box as a GFI-protected outlet. The GFI kills not just the outlet, but also the light switch. The GFI has shut off the power twice at other times, with no apparent reason, since the outlets were not in use, just the lights.
I know it's time to open the box and check for proper installation & grounding, but it's the TV interference that's interesting. Assuming yesterday's episode is repeatable, and not just a coincidence, how would a GFI cause interference? Other info: The TV cable enters the house right by the AC service box and crosses over the line to the bathroom at a right angle. And, I have BX cable.
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Doug Kanter wrote:

GFIs contain solid state amplifiers to pump up the signal from a miniscule leakage current to a level strong enough to energize an electromagnet which releases the "latch" keeping the line switching contacts closed.
Electronic design engineers will often complain, "I'm having a lousy week, my amplifiers oscillate and my oscillators won't!"
There is a *slight* possibility that the amplifier in that GFI was oscillating and froducing a frequency which interfered with your TV, and turning on the light changed the conditions enough to make it stop. But it's "not the way to bet" unless you can catch it doing the same thing a few more times, in which case I'd pop in a new GFI and see if the problem goes away.
HTH,
Jeff
--
My name is Jeff Wisnia and I approved this message....

(W1BSV + Brass Rat '57 EE)
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Thanks, Jeff. Sounds like the way to go, especially since GFIs are cheap. And, some of the wiring in this house was modified by the prior owner, who was 25 years old. Based on what I've seen so far, he knew about as little about home maintenance as *I* did when I bought my first house.
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My first house had some 'home wiring'. Shortly after moving in I found the first occurance where the previous owner had used an extension cord to wire in an overhead light and switch. I immediately called a licenced electrican in to check, repair, and upgrade where necessary. The big pile of fuses in the basement next to the service entrance should have sent up red flags for me. This idiot could have cost me my family or home. I imagine the insurance company would have something to say too.
Mike

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I haven't found anything quite that hideous yet, just minor stuff. I had a furnace repair guy here two weeks back because the 6 month old Goodman unit was starting & stopping very erratically. This guy was from a company I used for 20 years in my prior house, so I knew he was good. He verified what people frequently say in this group - the quality of the installation is a huge factor in how well a furnace works. He flipped through the installation manual (for my benefit) and pointed out a list of things that weren't done according to spec. Among other things, he pointed out that the installer had left the old BX cable in place, rather than switch to Romex, something his company does as a matter of habit when installing a new furnace. He explained that because modern furnaces have solid state circuitry, they're often fussy about having a perfect ground. Anyway, he fixed some of the little stuff and the unit's running fine now. I'll be running Romex shortly, and he'll be stopping back to connect both ends. (I don't stick my hands behind breaker panels).

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