Sunday, September 2, 2018

The Miraculously Self Healing LCD Screen

This is a story of triumph, heartbreak, redemption with a bit of stupidity mixed in.

I have an old Raspberry Pi Model A floating around my junk drawer that I wanted to find a good use for. While it isn't the fastest Pi out there anymore, it did have lots of life left in it and I wanted to do something useful with it.

That "something" turned out to be a little Internet of Things (IOT) device that tied into my Pi Aware installation to show a real time map of the aircraft flying around in my area, along with a real time radar view of the local weather. The information is displayed on a small 7 inch LCD screen that I bought off of ebay for around $30.

I will provide full step by step details on how I built this neat little gizmo at a later date, but this story is more about what happened after I just finished building it.

After testing and installing the electronics into the custom case that I built for this project, the final step was to install the back cover of the case. The back was built as a friction fit, so it took a bit of force (not a lot) to fit the back into the case.

Even though I took a lot of care in protecting the screen, when I put the new toy in its place of honor and plugged it in, I had a very ominous black line running down the center of the screen.

I had cracked it! After kicking myself, I immediately went back onto ebay and ordered another screen to replace it.

Since it'll take a good month for the replacement to come, I decided to keep using the bad screen in the meantime.

The screen was kept on 24 hours a day, and I hadn't really paid much attention to it until a couple of days later when I wanted to see if there was any rain headed my way.

That's when I got a shock....

The screen seemed to be repairing itself!

The black line on the screen is dramatically smaller

The black line was definitely a lot smaller. I kept an eye on it, and true enough, things improved further after a few more days. Things had improve so much in fact that the black line no longer impacted the active viewing area of the screen

Still getting smaller

What gives?

Typically when you see black spots or lines on your LCD screen, the safe assumption is that your screen is suffering from dead pixels. As the name implies that usually means that part of the screen is no longer useable and in the majority of cases, your screen is headed for the dumpster.

A quick Goggle search seemed to confirm that a dead pixel never comes back to life again, but a more reasonable explanation did come to light - "Stuck" pixels.

From Wikipedia:

"… Stuck pixels are often incorrectly referred to as "dead pixels", which have a similar appearance. In a dead pixel, all three sub-pixels are permanently off, producing a pixel which is permanently black... Dead pixels are much less likely to correct themselves over time or be repaired through any of several popular methods. Stuck pixels, unlike dead pixels, have been reported by LCD screen owners to disappear, and there are several popular methods purported to fix them, such as gently rubbing the screen (in an attempt to reset the pixel), cycling the color value of the stuck pixel rapidly (in other words, flashing bright colors on the screen), or simply tolerating the stuck pixel until it disappears (which can take anywhere from a day to years)..."

So in my case, what I really had were stuck pixels that had the appearance of dead pixels and the fix truly was to just leave it alone, it will eventually fix itself.

The lesson learned here is to not simply jump to the conclusion that you have a bad screen if you all of a sudden notice dark spots or lines on it.  Give it a few days first before you completely write the screen off.

In the meantime I need to dream up another project for the screen that I'm going to be getting in a few weeks...

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