escrocu
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Nov 21, 2019, 12:30 PM
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Sony KDL 40-R470A no backlight
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Hello,
The TV is a sony Bravia KDL 40-R470A manufactured in 11/2013. My background is IT engineer, I love to repair stuff, can use a multi meter, can solder things, but my theoretical electronics knowledge is basic.
SYMPTOMS : Sound works, backlight is gone, flashlight test shows picture.
So, my understanding is that the culprit is either the power supply board, backlight leds or led driver.
POWER SUPPLY BOARD: It's a Sony 1-474-487-11 (APS-349). I have tested the led output and it gives 74.8V (with the led cable connected or disconnected.) It's a 2 wire cable. In my opinion, this is not enough for the leds to be powered, as my TV has 10 strips x 5 leds/strip = 50 leds totally. 50 leds x 3v/led should give around 150v to power them. But that is only my assumption. I have no idea if this power supply is working properly or not. Is 75v a normal output or should it be around 150v? I can order a good used one for about 30 euros. Shipping costs around 15 euros and I have to wait around 10 days for it to arrive.
BACKLIGHT: I have no LCD led tester. Ordering one from ebay is around 10 euros but it takes 4-6 weeks to arrive. Getting one locally will cost 40 euros. I could use it to power the little led cable and hope to see the screen light up. I want to avoid waiting 4-6 weeks or paying 40 euros for a tester I will only use once. I could also use a 3v battery to test the leds individually. But that means I have to disassembly the TV, do the test and then order the backlight led strip (30 euros on ebay, 4-6 weeks sipping time) and reassembly back. I have no space to store it dissembled and I am afraid to do it twice as I might damage the screen. I don't have a hot plate to try to replace the leds individually and I don't have spare smds if I find any damaged ones.
LED DRIVER : I have no idea where it's located or how to test it.
For pictures of the power supply board check https://www.shopjimmy.com/sony-1-474-487-11-power-supply-led-board.htm
Please give me some advice. All the repair shops I called in my town, refused to only diagnose my problem and ask for around 100 euros for the repair.
Basically my question is : how can I diagnose my problem for sure without taking the TV apart in order to get to the backlight led strips? I don't think 74.8 V is enough to power all the 50 leds, but maybe it detects some malfunctioning leds and it doesn't provide more voltage. (I'm just guessing here).
Thanks for reading!
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