TV Repair By Mail

November 17, 2022 by Al Williams 49 Comments

I don’t think there was ever a correspondence school called the “Close Cover Before Striking School” but since book matches — which used to be a thing when most people smoked — always had that text on them anyway perhaps there should have been. There was a time when electronic magazines, billboards, and even book matches were constantly bombarding us with ads to have a career in electronics. Or computers. Or TV repair. So while we think of distance learning as a new idea, really it is just the evolution of these old correspondence schools which date back quite some time.

How far exactly? Hard to say. There’s evidence of some distance learning going back as far as 1728. In 1837, there was a correspondence course to learn shorthand. By 1858, the University of London started its external program for correspondence work and the University of Chicago had a home study division in 1892. Radio was an early choice of topic, too. In the United States, the United Wireless Telegraph company started a training school — later the Marconi Institute — in 1909. However, it is doubtful that there was any correspondence training going on there until much later.

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Compensating For Your TVs Backlight

October 10, 2022 by Matthew Carlson 8 Comments

[Pekka Väänänen] has a Panasonic TV with a broken backlight that creates an uneven pink/green color. While it isn’t a huge deal for most films, black-and-white films tend to show the most effect. So, by modeling the distortion as a function, [Pekka] set out to find an inverse function that corrects the distortion before it gets to the TV.

However, the backlight doesn’t emit enough light for some colors, which means the blue and green channels need to be dimmed. As mentioned earlier, the distortion isn’t even, so the distortion needs to be captured and then calculated.

He took a few pictures with his phone, corrected the perspective, and applied a blur. The camera also has some distortion but works as a first approximation, but that isn’t something he covered here. Next, he set up a webcam and pointed it at the TV, trying to find good gain and offset values with a bit of Python.

Now it just becomes a problem of minimizing the per-pixel difference. Ultimately he just went for a random approach rather than an annealing or hill-climbing approach. Now that he had a function to apply, it was just a matter of adding a custom shader to his video player, which includes a live shader editor. He had to hack in support for an external texture, but he is kind enough to include the shader code and the patch in the article.

The result is excellent, and it’s a great use for an old TV. But perhaps, in some cases, it might be worth replacing the backlight entirely.

From Trash To TV

April 24, 2016 by Jenny List 49 Comments

In days gone by, when TVs had CRTs and still came in wooden cabinets, a dead TV in a dumpster was a common sight. Consumer grade electronic devices of the 1960s and ’70s were not entirely reliable, and the inside of a domestic TV set was not the place for them to be put under least stress. If you were electronic-savvy you could either harvest these sets as a source of free components, or with relative ease fix them for a free TV set.

With today’s LCDs, integrated electronics, and electronic waste regulations, the days of free electronics in every dumpster are largely behind us. Modern TVs are more reliable, and when they reach end-of-life we’re less likely to see them.

[Sidsingh] happened to find an LCD TV in a dumpster, and being curious as to whether he could fix it or salvage some components, cracked it open to take a look.

He found that somebody had already been into the set and that some components on the PSU and backlight boards showed evidence of magic smoke escaping, having been desoldered by the previous repairer. The signal board was intact though, a generic Chinese model based around a Mediatek MTK8227 SoC. Information was scarce on these boards, but some patient research yielded a schematic for a similar set.

Once he knew more about the circuit, he was able to identify the power lines and discovered that the 1.8v line to the SoC was faulty. This he traced to a switching regulator for which there was no equivalent in his junkbox, so he substituted a linear regulator to obtain the required voltage. The CFL backlight was then removed and replaced with LED strips, and as if by magic he had a working TV set.

This might seem a relatively mundane achievement on the scale of some of the projects we feature on these pages, but it is an important one. In these days of throwaway items it is still not impossible to repair dead electronic devices, indeed as [Sidsingh] found the power supply is most likely to be the culprit. If you score a dead LCD TV then don’t be afraid to crack it open yourself, you may be able to fix it.

As you might imagine, many repairs have made it onto Hackaday over the years. Of relevance to this one is this LCD that inexplicably worked when exposed to light, an LED backlight conversion, and this capacitor swap to return an LCD monitor to health.