[Solved!] My TV Screen Flickers When Someone Flips a Light Switch

My TV flickers when someone flips a light switch. The video and sound both disappear for a second, then come back as if nothing ever happened. (Edit: solved! Details below.)

TV Flickering

The solution to removing the TV flicker is easier (and way less expensive) than I ever imagined. But it took some detective work. Here’s how you can stop your TV from flickering anytime an appliance or light switch is turned on.

In late 2016, I mounted my TV on the wall and moved my cable box, modem, wireless router and XBOX 360 into a closet on the other side of the room.

 

TV Mounted Over Fireplace

I connected the closet to the living room wall with CAT6 and HDMI wall-plates, and added some new electrical outlets at both ends. (I’ll do a more in-depth article on this project soon).

The installation went very well. It took multiple nights and weekends, but I learned a lot about the limitations of HDMI, how to run cable through walls and terminating CAT6 cabling.

In the end, everything worked extremely well. Except for one thing:

When someone flipped a light switch, my TV would flicker.

AV Closet

This didn’t happen before I created the AV closet.

Not only that, but whenever an appliance turned on, the TV screen would flicker. Anytime the dishwasher would come on, the TV screen would flicker. Anytime the pump for our septic system would come on, the TV screen would flicker. Anytime the compressor for our refrigerator would come on, the TV screen would flicker.

This was very annoying. In the best case, it would only happen about once an hour. But in the common case, it would happen once every 10-15 minutes.

It got to the point where my wife would just look at me and shake her head.

I work on software during the day, so I’m very used to debugging problems. It was time to put my thinking cap on and see if I could figure out how to stop the flickering.

Debugging the problem

I was a little nervous. My electrical experience consists mostly of replacing outlets and switches. I’m the epitome of a weekend warrior (and a dangerous one, at that).

Basically, I didn’t know what I didn’t know, and I was afraid that I had a lot of work ahead of me. What if I needed to rewire both the closet and the living room? I had already patched and painted, and mounted the TV.

I, of course, started with searching Google. I searched for every combination of keywords under the sun:

  • “my tv flickers when the lights come on”
  • “my tv turns black when my dishwasher starts”
  • “lose TV video electricity”

There were a couple of common frequent causes to the TV flickering problem. And all of them made me nervous.

Potential Cause 1: TV Flicker Caused by Voltage Fluctuation

Voltage Fluctuation

Most of the answers were coming back were similarly. Essentially, when the dishwasher starts up, the appliance pulls a lot of electrical current to start the motor. This fluctuation in current could be sending a dip or surge to the TV.

This sounded reasonable to me. The suggestions were to make sure that these appliances and the TV were on separate circuits.

Installing a Wall Outlet Behind a TV

Except I was sure the TV was on it’s own circuit because I added a new circuit just for the TV when I did the installation. If they’re on a different circuit, then it can’t be voltage fluctuation.

Potential Cause 2: TV Flicker Caused by Electromagnetic Interference (EMI)

Once I stopped considering voltage fluctuation, I noticed another big pattern in the solutions.

There’s a possibility that either my TV or my cable box was getting some kind of electromagnetic interference from elsewhere.

According to this page, “EMI (electromagnetic interference) is the disruption of operation of an electronic device when it is in the vicinity of an electromagnetic field (EM field) in the radio frequency (RF) spectrum that is caused by another electronic device.”

Lucky for me, I have a family member who likes this kind of stuff. He validated the possibility due to the TV’s proximity to my fridge. We talked about adding a faraday cage around the TV’s electrical outlet or adding a line filter to reflect the EMI.

But, we decided that it was unlikely to be EMI since there were large appliances elsewhere in the house that would also cause the flash.

OK, so if it’s neither voltage fluctuation, nor Electromagnetic Interference, what else is there?

Did You See That?

I was still at a loss, and hadn’t made any changes to the setup yet.

We were sitting on the couch one night watching the West Wing on Netflix. For whatever reason, I always need to turn the volume up on my TV when watching Netflix.

West Wing

So I naturally go to turn the volume up when the TV does its very annoying flicker.

And then I noticed it.

The video and sound from the X1 box blacked out as usual, but the volume indicator on my tv didn’t flicker along with it.

Now we’re getting somewhere!

It’s Actually Not the TV!

All my research and thinking had been focused on the TV.

But, if it was the TV, the volume indicator would have flickered alongside the audio and video.

Because the volume indicator stayed on the screen when the video and audio flickered, I was sure it wasn’t a problem with the TV.

It was either the cable box, or the connection between the closet and the living room.

Option 3: TV Flicker Caused by the CAT6 Connection

TV Flicker Was Not Caused by HDMI Extender Wall Plate

I connect the devices in the closet to the TV through CAT6 and these HDMI extender wallplates.

This is the poor man’s setup, and is more prone to problems since the sending HDMI wallplate just maps the HDMI pins to wires in the CAT6. Then, the receiving HDMI plate on the other end knows what should be where and reverses it for display in the TV.

This is the method I chose primarily due to cost. At less than $40, these wall plates are an afforable alternative to the more expensive HDBaseT HDMI extender over Cat6.

Could I Reduce TV Flicker With an HDBaseT HDMI Extender?

I started to think that this relatively flimsy setup may have increased my risk for something to go wrong there.

I tested this by playing NHL 15 on my XBOX360 for an hour.

Seriously. Anything in the name of making my wife happy, right?

When I didn’t get a flicker, I need to confirm that it wasn’t just coincidence, so I forced the septic pump to turn on and off.

And guess what: no flicker!

I could confirm that the connection between the closet and the living room was working as expected because the XBOX didn’t flicker.

Narrowing In On the Cable Box Causing the TV Flicker

My Xfinity X1 Cable Box Was Causing TV Flicker

When I couldn’t get the XBOX to flicker, I narrowed in on the cable box.

I validated this by re-connecting the cable box and forcing the pump on and off again.

It flickered. This is what I was hoping for, and is likely the only time I wanted to see flicker.

But, I’m not sure what about the cable box is causing the problem. I don’t know enough about the X1 to even start debugging what could be causing the TV to flicker.

What I knew at this point was that the TV was fine, the CAT6 connection was fine, and the XBOX was fine.

I had two options: it’s either the Coax cable connection from the main line to the cable box, or it’s the HDMI connection cable box and the wall plate.

Everything I had read said that it’s unlikely that an HDMI cable is “mostly bad”. An HDMI cable can’t be kinda broken: it either works or it doesn’t. And in my case, this HDMI cable had been delivering audio and video reliably for years.

But in this case, the HDMI cable was the easiest to test, so I tried that first.

My TV Flickered Because of the HDMI Cable

I removed the HDMI cable from the cable box, and replaced it with the HDMI cable from the XBOX.

Then I crossed my fingers and forced the septic pump on and off. And guess what?

The TV didn’t flicker!

I validated this crazy idea by swapping the cables back into their original positions and forcing the septic pump on and off. The TV flickered again, validating my solution.

But… Why?

If you trust the Internet, you’d never even consider the HDMI cable to cause this issue. But let me tell you first hand: since replacing the original HDMI cable with a new one, my TV hasn’t flickered once.

I was curious, though: what was the difference between these two HDMI cables? How can I make sure that I don’t buy an inferior HDMI cable again?

Looking over the malfunctioning HDMI cable, I don’t see any kinks or failures in the cable or terminal.

Even the text printed on the cables is exactly the same:

CTI AWM 20276 VW-1 80°C 30V E81280-D CHING TAI

I’m honestly not sure why this new cable worked when the other didn’t. I noticed that the connectors on each cable are a little different, but that’s it.

The only possibility I can think of is that the working cable might be newer. Probably like anyone reading this post, I’ve got a hundred HDMI, ethernet and USB cables sitting in a box that I’ve been collecting for years. Who knows how many times they’ve moved apartments or cities, or how I may have inadvertently damaged them.

(Sidenote: if you read this and have any idea why one HDMI cable would have worked correctly while another didn’t, please let me know! I will update this article and credit you.)

Try a New HDMI Cable First to Solve Your TV Flicker

Replacing an HDMI Cable Stopped by TV Flicker

I know the instinct: just grab a new one from that box. That’s what I did, and it actually caused the problem. (One could argue that’s what I did to also solve the problem, but I’m chalking that up to coincidence.)

Plus, new HDMI cables are cheap: $5.99 on Amazon (free shipping with Prime).