Friday, August 4, 2017

E470i LED Back-lit TV Repair

I picked up a 47 inch LCD TV with LED back-light that was no longer working.  I discovered that these LED back-lit TVs have the LED's wired in series and that eventually one opens up and the lights go out.

To dissemble the TV start by removing the back cover.  Then remove the metal cover in the foreground of the next picture it covers the LCD Connectors.

The cables need to be un-taped before they can be disconnected.  There is a black lock that flips out to release the cables.
Then remove the front bezel.  Besides lots of screws on all four sides there are some tabs across the bottom as can be seen in the front center of this picture.

Then there are several catches that will need to be unhooked.

The screen lifts out, being careful about the ribbon cables that are still connected to it.  Then there are four metal strips that hold the back-light filters in place.  There is a solid plastic filter and three flexible filters that will fall out if you are not careful.  Be careful to keep them in the right order but set them somewhere out of the way.
 Next is to remove the last layer covering the LED strips.  You will need to remove the pins that hold the plastic back and control the spacing to the front.  Two of them are under the power supply board.
 They are removed by pinching them with needle nose pliers on the back side.

Now to remove and test the LED strips.  They can be carefully pealed up with a flat blade screwdriver.  I used my fingernails to get underneath them to start the process.  Each strip has 4 or 5 three volt LED's (12 to 15 volts).  You can use two old 9 volt batteries to test them.  There should be a 100 ohm resistor in series with the batteries.  The end strips are tested by applying power to the test points near the connector.  The middle strips are tested the same way but you will need to short out the opposite end connector.

You will likely find 2 dead strips and maybe some dead LED's as well.  I actually broke one LED strip in the process of removing it.
Once you have the LED strips replacements you can test them out by removing the power distribution bad and testing them out like in the following picture before reassembling everything.  Remember that there are two sets of LED strips.

Here is a video on testing LED strops with 9 volt batteries:

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