Televisions

Why Does My Screen Go Blank?


We’ve probably all experienced it. We are watching a channel and then switch. When we do, the screen goes blank for a few (or perhaps many more) seconds. This happens most often when changing channels on cable TV or when we switch inputs. But why? Why does the screen blank out and then come back?

HDMI Handshake

Troubleshooting HDMI issues can be a hassle, but blank screens are actually part of HDMI. When HDMI devices are connected by an HDMI cable, a handshake occurs. This allows them to communicate with each other in order to establish working parameters (it’s called an EDID or extended display identification data but that’s not important here). The display will tell the receiver or source what resolution it can accept. Receivers tell sources what audio and video it can pass through or decode. Sources tell everything else what audio and video it has available to send.

This ensures that you get audio and a picture when you connect your HDMI cable. Before, if you set the resolution or outputs of your devices incorrectly, you’d get no picture, no sound, or both. That is no longer supposed to happen with HDMI (though it can sometimes).

HDMI Doesn’t Like Change

So, this handshake sounds great, right? Your TV always gets the highest resolution it can display, your receiver always gets the highest quality audio it can decode. But there is a catch. This handshake is not instantaneous. It takes anywhere from a couple to many seconds for it to complete. And while your devices are setting up the handshake, you have nothing to see or hear.

When switching inputs, the HDMI handshake has to happen again. That’s why you’ll sometimes get a blank screen when you switch inputs. Manufacturers have introduced methods to reduces this time. Fast switching is accomplished by establishing a handshake with all inputs when the TV or device is powered on and then maintaining the handshake regardless of which input is actually being used. This will reduce (but not eliminate) the amount of blank screen you see when switching inputs.

But that doesn’t work when you are on the same input. When you are switching channels on your cable box, you’ll sometimes see a blank screen. This is because the two channels have different video resolutions. You’ll notice it most commonly when switching between high definition and standard definition channels.

HDCP

This process isn’t slow just because the devices are hashing out what video and audio to send. Along with the handshake, we got HDCP or High Definition Copy Protection. Many years ago, our AV overlords decided that they wanted more control over whether or not you could make copies of content. These were the heady days of VHS when you could record your favorite shows and even make copies of VHS tapes you purchased. So they came up with a plan. They’d add copy protection to everything, including our home theater systems. To do so, they’d need a new cable. One that had copy protection built-in. They knew we’d never agree to that. So they put it in a pretty container. That container? The promise of a single cable solution.

During the handshake, each device needs to authenticate that it is a real, approved HDMI source. This is so that you can’t just buy an “HDMI recorder” that you can plug your Blu-ray player into and start burning copies of your favorite movie. When using fast switching, all the display and audio information is sent and saved, but the HDCP authentication can only happen on a single input at a time (the one in use). That’s why there will always be a little bit of blank screen when switching inputs.

Fixing Blank Screens

If you don’t have a device that can utilize fast HDMI switching, and you are annoyed by blank screens when switching inputs, look into getting one. Almost all newer displays will come with fast switching.

If you are experiencing lots of blank screens when switching channels, there are a couple of things you can do. First, if there are SD and HD versions of the same channel, go through your guide and remove the SD versions. This will at least keep your family from accidentally watching the SD version and causing more blank screens.

Second, you can go into your cable box’s settings and force it to use a specific resolution. Rather than putting out whatever the channel is distributing, you can have it upscale everything to a specific resolution. Once it creates a handshake with your display, it won’t have to do it again. While this isn’t a perfect solution as it can sometimes cause scaling artifacts, it will reduce or eliminate the number of blank screens you see when changing channels.

Have you experienced blank screens? What was the issue and how did you fix it? Let us know in the comments below or on our Facebook page!


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