Sony Bravia 55 KDL-55EX640 no backlight / flashes once

[budm]

Re: Sony Bravia 55 KDL-55EX640 no backlight / flashes once

OK, that is pretty well focused pictures, I will have to download and trace out the connections and draw up simple diagram to see how the LED strings get the power to them. So wait until tomorrow when I have more time.

[budm]

Re: Sony Bravia 55 KDL-55EX640 no backlight / flashes once

BTW, what are the DC A scales do you have on your meter? Can I see the picture?

[triplefour]

Re: Sony Bravia 55 KDL-55EX640 no backlight / flashes once

heres my voltmeter

[budm]

Re: Sony Bravia 55 KDL-55EX640 no backlight / flashes once

OK, put the meter on A DC 10A scale, you will have to move the red probe to the 10A socket, too bad your meter does not have 2A scale, hopefully it is sensitive enough to see some action on the meter.
You will have to cut the wire one at time on the connector CN3, the wire should be cut so you can splice the wire back together.
You can start by cutting the wire on CN3 PIN 1, then strip the wires so you have expose conductors, then you will put the meter probe on each expose conductor, you should wrap the conductor on the probe tip and tape it up.
Then turn one the TV, if the LED string does not have open circuit you should see the reading jumps up before it goes into shutdown. You will have to do the same on the other 3 wires as well to see which one show no action on the meter.
As you can see in my picture, I use clips for making connection, the reading on my meter shows around 300mA, your meter may show something like 00.2 or 00.3. BTW, do not worry about the probes polarity.
https://www.badcaps.net/forum/showth...t=25810&page=5

[triplefour]

Re: Sony Bravia 55 KDL-55EX640 no backlight / flashes once

ok i am about to do this. should i do this for CN4 as well?

oh wait i think i get it now... cn4 is all the negatives only

[triplefour]

Re: Sony Bravia 55 KDL-55EX640 no backlight / flashes once

i just tested cn3 pin1 and i didnt see anything happen on my voltmeter. even when i put it on 200ma

[triplefour]

Re: Sony Bravia 55 KDL-55EX640 no backlight / flashes once

i didnt want to cut any wires so i figured out this way of doing it instead. i just removed the wire from the harness and wedged the probe in there
and then used a bit of wire to splice the other probe to LED wire. i used my other meter to test continuity between the black probe and the pin to verify they are indeed touching.

but on pin1 and pin2 of CN3 i still see no activity on my meter in 10a or 200ma

the only thing i noticed is sometimes the negative sign flashes for a moment on my meter

[budm]

Re: Sony Bravia 55 KDL-55EX640 no backlight / flashes once

The negative sign is just telling the direction of the current flow, what we are looking for is the inactivity of current flow when the circuit has open connection due to bad LED that has gone open circuit in the LED string, the protection circuit monitor the current flow through each string and maintain the constant current flow to give steady backlights, if the LED goes open circuit, the voltage will rise, then the protection circuit will shutdown the LED power supply.

[triplefour]

Re: Sony Bravia 55 KDL-55EX640 no backlight / flashes once

well i only tested pin 1 and 2 but they both seemed inactive. either that or im not measuring it right? could they both be open?
can the LED strings be changed or repaired?

[budm]

Re: Sony Bravia 55 KDL-55EX640 no backlight / flashes once

You may want to read this thread:
https://www.badcaps.net/forum/showth...TRIP%22&page=4

[triplefour]

Re: Sony Bravia 55 KDL-55EX640 no backlight / flashes once

im reading and trying to understand but a lot of whats in this thread is over my head....
am i going to have to open the panel and take out the LED strips?

[budm]

Re: Sony Bravia 55 KDL-55EX640 no backlight / flashes once

Yes, just enough to see which LED strip does not light up to narrow it down first, but if you never take the LCD panel assembly apart before you can easily damage the screen.
Unless some body else has better ideas.
This might work, you can have just one of the four wire connected and see which one does not show a flash of backlights for seconds, you should observe it in dark room.

[triplefour]

Re: Sony Bravia 55 KDL-55EX640 no backlight / flashes once

yes i will try that first. i REALLY dont want to take this panel apart. its HUGE and its a clients TV and if i damage it i cant afford to replace it.

[budm]

Re: Sony Bravia 55 KDL-55EX640 no backlight / flashes once

I avoid taking the panel apart myself unless I have to also.

[triplefour]

Re: Sony Bravia 55 KDL-55EX640 no backlight / flashes once

ok after testing and re-testing, i cant seem to get any reading of amps with my meter. i have concluded that the pin1 and pin2 are not lighting up the backlight at all though. pin3 and pin 4 by themselves or together, always light up the backlight for a flash.
pin 1 and 2, together or by themselves, never flash the backlight.
but since i cant tell whats going on with the current, how do i know if its the LED strip or if the pin is just not supplying the current? i can tell it supplying volts but i just cant read the current for some reason, on any pin!

[triplefour]

Re: Sony Bravia 55 KDL-55EX640 no backlight / flashes once

can i switch the wires so that pin 3 and 4 lights LED strip that was plugged into 1 and 2 ?

[triplefour]

Re: Sony Bravia 55 KDL-55EX640 no backlight / flashes once

ok after doing a BUNCH of wire swapping and testing ive noticed a few things:

the wire sequence for CN3 is
pin/color
1-white
2-white
3-black
4-blue

im to beleive that each of these wires powers a different LED strip but i cant see it for myself since i didnt open the panel yet.

anyway first i tried each wire by itself. found that both white wires on pin 1 and 2 dont produce any flashing of their LED strips
i found that the black wire (pin 3) and the blue wire (pin4) both produced backlight flashes. but the blue wire was noticeably dimmer of a flash.
also if i keep turning on and off the TV, the blue wire's flash eventually gets dimmer to the point where u cant even see it anymore.
the black wire (pin 3) gets a little dimmer on the second flash but then remains the same brightness on future flashes and i can turn it on and off many times. it never becomes dimmer than on the second flash.

so then i moved on to switching wires around.
i tried the black wire on each of the pins
on pin 1,2, and 4 it would flash, but dimmer than on pin 3, and repeated flashes would get even dimmer until you just cant see it. maybe 2 or 3 times before u cant see it anymore.

the blue wire does a similar thing on all pins but overall just dimmer than the black wire.

the white wires do nothing no matter which pins u plug them into.

i am having trouble guessing what is going on here? why does it get dimmer on successive flashes with all but the black wire on pin 3?

why do the white wires do nothing? are both of those LED strips completely failed?

if the black wire's LED strip is fine (since its the best performer), then why does it shine dimmer on the other pins, and eventually not even flash at all?
too many variables

also can i even order replacement LED strips, or do i have to replace the LED's themselves?

[budm]

Re: Sony Bravia 55 KDL-55EX640 no backlight / flashes once

I trace out the board, yes each one of those are for each LED sting (4 strings), the wires are connected to each Anode of the each LED string, the return wires on the CN4 are the Cathode side of each LED string.
I say 1 (white) has open LED/s in that string. You can have more than one failed string.
At this point since it is customer's unit, I would inform them that the TV needs new LCD panel, if they let you keep it then you can use it as learning tools to how LED panel functions and you can take the panel apart to see what are inside.

[triplefour]

Re: Sony Bravia 55 KDL-55EX640 no backlight / flashes once

cant i tell them i can take a chance at replacing the LED strings?
and how can i be sure that its bad LED strings and not a bad converter?

[Clydeuk]

Re: Sony Bravia 55 KDL-55EX640 no backlight / flashes once

I would tell them the truth, that you believe the LED strings have failed, that if they take the set to a repair shop they will receive a quote/bill for a new panel. Then tell them that if they are prepared to risk damage that you are willing to investigate repairing the panel. Just let them know the risk involved so that you don't get lumbered if the panel does get damaged, since a new panel is the normal course of repair here.