I bought a new 32" Insignia HDTV and hooked it up to my rooftop antenna. I have an inline signal amplifier with ac power hooked up too. All worked well for a day and then the next morning the digital signal was fluctuating wildly from 80 to 0 and back again. I hooked up a digital converter box and ran the coax through that instead of directly into the TV. All was well again. Remove the box, though, and the signal fluxs again. So I took the TV back to the store and told them the tuner was bad.

Exchanged it for a Toshiba 'cause I suspected the tuner in the Insignia was Chinese-made. Hooked it all up again, without the converter box, and all was well. Next day, the signal is fluctuating again. Wild swings from high to nothing to high again.

An alternate TV in another room is analog and connected to a digital converter box. It performs flawlessly. No signal fluctuation even when the signal on the Toshiba is.

Of course, my next step is to remove the signal amp from the equation and see what happens to the Toshiba. Unfortunately, the area has poor signal reception... thus the need for the inline amp. I won't be able to make this change for another few days as I'm not in the area right now, but I've been thinkin' on this for days.

My question: could the ac powered signal amplifier be causing this? Is it possible a powered signal amp can damage or interfere with the TV tuner?

Try swapping the outputs on your splitter or on power supply if built in, Check cable connections, did you use screw on fittings? Hope not, they will work but must screw onto shield strands of cable.

It's suspicious of a "ground loop" or "DC on the antenna terminals from the pre-amp"
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Does the TV use a 3-wire cord?

You can try connecting two 75:300 matching transformers Indoor/Outdoor Matching Transformer - RadioShack.com (http://www.radioshack.com/product/index.jsp?productId=2103912)

Back to back and insert in series with the RF and see if it goes away. You will lose a little bit of signal this way.

This will also work for a DC Block:
PE8240 - D.C. BLOCK F MALE TO F FEMALE; 10 MHz - 2 GHz - DC BLOCKS (http://www.pasternack.com/product-D.C.-BLOCK-F-MALE-TO-F-FEMALE-10-MHz--2-GHz-PE8240-72032.html)
I was thinking a intermittent connection.
A meter will show a presence of voltage.
When signal drops to Zero on that TV, what happens to the other(s)?
What Amp are you using? Mast mounted?
Antenna Preamps will have a Power supply that supplies voltage up to antenna preamp, providing power, then send back on same coax to power supply with the amplified signal, then a built in capacitor is used to remove voltage, many have 1 or 4 outputs, some have adjustable gain, and an FM trap.

Just not at $72.00 each. Try here: DC Voltage Block Connector Adapter 75 Ohm F-Type Winegard VB-1000 Voltage Block Female to Male 1 Pack Coaxial Coupler for IR Over Coax Cable Systems Audio Video AC/DC Volt Blocking Adapter Connector, Part # VB1000: Oak Entertainment Centers and Home (http://www.summitsource.com/dc-voltage-block-connector-adapter-75-ohm-ftype-winegard-vb1000-voltage-block-female-to-male-1-pack-coaxial-coupler-for-ir-over-coax-cable-systems-audio-video-acdc-volt-blocking-adapter-connector-part-vb1000-p-7062.html?manufacturers_id=2)

$1.95

KISS, glag you caught the price. I believe I used to get them from Radio Shack for about $3.00.

I caught the price because I was familiar with the company. They used to have a $100 min.