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Uh oh – Element ELCHW402 TV has given up the ghost July 22, 2012

Posted by truthspew in Uncategorized.
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I bought this in December of 2010 – so here we are a year and a half later of constant use and came home today to a red light on the front of the unit but it won’t power up. Soon as I saw that I knew what it was.

Of course because the standby is a the red light Keyron was all confused. I finally convinced him that it is the power supply for the television that is having issues. This is a common failure mode on virtually every HDTV set out there.

The issue will delve into electronic theory just a little bit.

AC line voltage here in the U.S. is nominally 110V AC (Alternating Current) and can go up to 125V AC (Which it is where I live).

If you were to hookup an oscilloscope to the AC line you’d see something that looks like this:

Sine wave

Now the terms on the image change ever so little on the scope, the Amplitude side is the voltage, and time remains constant.

Electronic logic doesn’t play nicely at 125V AC. So what you do is use a transformer to step it down, then you use a thing called a bridge rectifier. A bridge rectifier makes a semblance of a DC voltage but with serious amounts of what is called ripple.

This image shows the effects of rectifying the incoming current:

Ripple Explained

See the bottom of that image? The voltage rises and falls multiple times. To smooth that ripple out you use capacitance. A capacitor is a device that stores charge electrically. It’s usually comprised of two plates, separated by some dielectric, in many cases air.

And it’s job is to store up current quickly, and release it to smooth out the dc voltage.

In the case of the television we have, they use electrolytic capacitors:

Electrolytic capacitors

You’ll note there are two values on an electrolytic capacitor that are key – the capacitance which is measured in microfarads, and a voltage rating.

Manufacturers of HDTV flat panel LCD sets are notorious for using capacitors with too small a voltage rating. And when the filtering goes kaput, the television will NOT power up.

The solution, at least 99.9% of the time is to yank out the power supply board, get all new capacitors of the same microfarad value but in a higher voltage level. And it’s good not to get Won Hung Lo capacitors from China. Get good ones, quality ones. You might spend $20 or $30 on parts. Labor is probably 2 or 3 hours. Now in my case I know my labor rate, it’s $50 an hour for electronics work so $150+$20 = $170 to repair the set. As opposed to spending $300, $400, or more to replace it. You see what I’m getting at here.

So tomorrow I’ll tear it apart and then get online at mouser, Allied, or any of the big electronics distributors and order the capacitors to replace. I’ll also be able to do a visual inspection and see if there are any bulging capacitors in there.

I’m so happy I know how to push electrons around. And come to think of it, we probably experience a power spike, what with the vicious thunderstorm last week. That would be enough to push a weak capacitor over the edge.

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Comments»

1. John McGrath - July 22, 2012

Fascinating. But my 30 year old TV works just fine.

truthspew - July 23, 2012

Yeah – we were talking about that earlier. As I said, this is a common failure mode for virtually every LCD screen out there.

2. Wendell - February 11, 2013

thats what happens when people buy chinese made junk, these sets not worth repairing.


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