May 11, 2019

When a pixel is only showing some colors, but not all colors, then you might wonder what the problem is – and most importantly – how to fix it!

As you begin to light up your Christmas light display, over time you may start to see some of your pixels failing. While the overall failure percentage tends to be low, failures do happen.

But – the last thing you want to do is replace the pixel, and then find out that this was not the problem!

But before you grab those wire cutters, we have a few things to test and verify whether the pixel is indeed bad!

How to Troubleshoot Pixels that Only Light in Some Colors

If you haven’t changed ANYTHING in your display, and suddenly there’s a bad pixel, then there’s a 90% or greater chance that you do indeed have a bad pixel – even if it still lights up in some colors!

But – if you have just put up your display for the first time, or changed anything (controller, number of strings, wiring methods, sequence files), then we have a few things to check and rule out to get this pixel working right!

Test Patterns

The first thing that I like to do is to simply start with some test patterns from within the controller. I like to use something that flashes red, green, blue, and white (if your controller has one), to see if the pixel works.

The “Test button” on many popular controllers can be hit multiple times to view a nice test pattern.

If this makes the pixel work (but the pixel didn’t work with your sequences), then you know that the problem is most likely in your software’s patch or other configuration.

If you can make it light up in test mode, then you have verified that the pixel and controller are physically working.

Check The Controller

Then let’s head to the controller. The source of the problem we’re having often originates in the DMX protocol that is the basis of the e1.31 sACN, or Art-Net signal that we send our lights.

In these protocols, we get 512 channels of control for each universe of lights. With RGB LED pixels, we can fit 170 pixels into that, taking up 510 channels – with 2 left over.

Most often, in Christmas lighting, we just throw away those 2 channels and move on to the next universe. However, that’s not always the case and most controllers offer a method to switch between skipping those channels and not!

When this setting is wrong in your controller’s software, you’ll get a pixel that lights up in some colors, but not others. Make sure it’s set correctly for how you have designed your display!

Next, go and verify that the output you are using for your pixels is set the number of pixels that you have connected (or more).

Once you’ve verified that these are set correctly, you can run a test pattern from your controller again and see if it changed. If so, you’ve fixed it! If not, it’s time to dive into your sequencing/playback software.

Check Your Software

Once you’ve verified that your controller is set correctly, you need to verify that your sequencing software has correctly patched the correct pixels in the correct places and that the total number of pixels per universe is set to match your controller.

Number of channels per universe in xLights.

While it’s most important to verify the number of channels is set correctly, it’s also important to verify that your lights are connected to the correct prop. I like to do this by creating a test sequence that simple lights up and runs a slow animation on the pixels in question!

Check Your Lights

If none of this fixes the problem, then it’s most likely the lights. However, the one thing we haven’t ruled out is some kind of anomaly with your controller.

The last troubleshooting step I like to take is to plug in a spare set of pixels that you have around. You’ll plug them in to where the troublesome pixel is, and see if they all light correctly. If you find a pixel that has problems in the new string, then you know the issue is not with the pixels themselves.

If, however, the new string of pixels works fine, then you know that the problem is with the pixel.

Next Steps

Changing out that bad pixel doesn’t have to be a chore! In fact, I’ve written my guide to repairing bad pixels here.

The short answer – if you keep some extra pixels on hand, this will be much simpler, as you won’t have to rush to get your display back up for the next night’s show!

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