A friend of mine had this defective TV set and wanted me to take a look at it.
When plugged in the red led would light up and you could power it on to get a green led, but there would be no picture, just a black screen.
That it could actually turn on and go from red to green led could be a indicator on something wrong with the image / input boards, but as no back light turned on either I would start to take a look at the power supply.
The power supply is almost always the fault when flat screen TVs refuse to turn on.
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What to look for
Taking the TV apart was no problem, just some few 30 screws around the frame and we are inside to view a main board and a power supply board.
The power supply was pretty compact and it was hard to see all the components for the heat sinks and plates covering them. I pulled out all the plugs and could measure +24VDC for the back light inverters, +12VDC for the image / input boards, but two of the four +5VDC only measured +0.3VDC.
There was one slightly popped 1000 uF / 16V CapXcon capacitor at top of the power supply. Hidden underneath the plate over the heat sinks was another four capacitors that looked to be in bad shape. No wonder when they are crammed in between two heat sinks with a roof, it would impossible to dissipate any heat from there.
I upgraded the all the capacitors to the same capacitance, but from 16V/25V to 35V/63V rated 105ºC capacitors. Capacitor life time depends highly on supplied voltage vs rating and temperature. By using capacitors with a higher voltage rating it should help them live considerable longer. I also moved that largest ones out from the heat sink trap. That two others was not as damaged and therefore I left them in their original place and now with a little better air flow with two capacitors moved away.
The popped CapXcon capacitors measured:
– 1000 uF / 16V: only 33 uF and 43 uF
– 470 uF / 25V: 215 uF, 300 uF and 453 uF.
I used capacitors that I de-soldered from other electronics to replace the popped CapXcon capacitors, turning the TV on revealed that it was fixed and now able to show a steady picture.
All I used was some common electronics knowledge, a soldering iron and 5 capacitors that I had from other old electronics.
Bottom line: I repaired a 40″ Sodium LWD400-SI LCD TV for free and spent about an hour on it.