Samsung QE82Q70RAT no backlight

[EazyBone]

Yes! And that's with TV on? I'll have to look through thread again but I'm positive some of those should be 3 volts. Maybe we on to something

[EazyBone]

Do you have a legend like this one does? If so does it show it as 3v point 1?

[sansanpartida]

the socket between PSU and LED driver boards are rail supply
we are interesting on the socket between LED driver boards and MB this is the key control of signal

So that is what I have on the 16-pin connector CN9001A. (I didn't measure the serial pins since I don't think a reading with the multimeter will be relevant. Just tell me if I should measure it or scope it.)

Pin	Name	Measure
1	GND	0V
2	SEAMLESS	0V
3	GND	0V
4	SCL_LED	2,71V
5	BLU_ON/OFF	3,223V
6	TEST_SD	1,38V
7	SDA_LED	2,70V
8	GND	0V
9	TEST_LD	0,9V to 1,2V
10	VSYNC_IN	Skipped
11	SERIAL_STT	Skipped
12	SERIAL_UHR	Skipped
13	SERIAL_DATA	Skipped
14	GND	0V
15	GND	0V
16	CONTACT	0V

[sansanpartida]

Do you have a legend like this one does? If so does it show it as 3v point 1?

You are right I have the pin description table and I'm sorry I cropped it on my previous closeup picture I totally missed it. Here it is and you are right it show 3.3V... Do I have so bad luck that I've managed to order a defective driver board? 😥

[Diah]

So that is what I have on the 16-pin connector CN9001A. (I didn't measure the serial pins since I don't think a reading with the multimeter will be relevant. Just tell me if I should measure it or scope it.)

Pin	Name	Measure
1	GND	0V
2	SEAMLESS	0V
3	GND	0V
4	SCL_LED	2,71V
5	BLU_ON/OFF	3,223V
6	TEST_SD	1,38V
7	SDA_LED	2,70V
8	GND	0V
9	TEST_LD	0,9V to 1,2V
10	VSYNC_IN	Skipped
11	SERIAL_STT	Skipped
12	SERIAL_UHR	Skipped
13	SERIAL_DATA	Skipped
14	GND	0V
15	GND	0V
16	CONTACT	0V

MB are fine... driver boards or LED fault

[EazyBone]

I think also, I was able to find which pin number 1 on that legend was connected to, to the main board connector. When the connector was plugged in (all normal) that pin read 1.4v for me but when I disconnected the connector from LED driver to main and then tested that same pin (now at main board) the voltage was 3v.

Let me know if that made sense lol.

And I don't know for sure. But as that picture shows when it was working correctly for me that line was 3v.

See if you can find the pin 1 is connected to, to the main board

[sansanpartida]

I think also, I was able to find which pin number 1 on that legend was connected to, to the main board connector. When the connector was plugged in (all normal) that pin read 1.4v for me but when I disconnected the connector from LED driver to main and then tested that same pin (now at main board) the voltage was 3v.

Let me know if that made sense lol.

And I don't know for sure. But as that picture shows when it was working correctly for me that line was 3v.

See if you can find the pin 1 is connected to, to the main board

Sorry, I don't think I understand your message..
- If I unplug the cable coming from the motherboard and going to the driver board with the TV ON: I read 0.7V.
- Then, as soon as I plug in the cable, I have 1.36V.

[Diah]

I think also,

this set had edge or direct LED BL..? if edge tester will report fine but there fault at protect led zener

[sansanpartida]

I'll test the backlight again tomorrow. I'm exhausted right now. Can someone write me a quick and comprehensive guide on how to test the LEDs to exclude a faulty LED strip assembly? I quickly tested all the ribbons with 84V and really low current, and the light was really faint. I thought that was OK, but maybe that doesn't mean the strip is fine...

Thanks in advance. I really appreciate your help!

[EazyBone]

this set had edge or direct LED BL..? if edge tester will report fine but there fault at protect led zener

This is full array backlights

[EazyBone]

I'll test the backlight again tomorrow. I'm exhausted right now. Can someone write me a quick and comprehensive guide on how to test the LEDs to exclude a faulty LED strip assembly? I quickly tested all the ribbons with 84V and really low current, and the light was really faint. I thought that was OK, but maybe that doesn't mean the strip is fine...

Thanks in advance. I really appreciate your help!

Turn the tester to max volts/amps like I said. When not touching anything it'll read 330 or something and then when you test each led strip it should give like 100 milliamps and 84.6 (or whatever voltage) across the board then. There will be 64 light strips to test.

If you were getting them to light up dimly you were doing it right.


Make sure that switch is NOT on 1ma, set it all to max.

Then like I said, move down each pin on each side as you were doing. BUT if you don't have the 3.3 V to led driver. That's probably the issue.


And as for your 1.4v drops when disconnecting, yes you did that test fine and maybe I was mistaken on my numbers. But I think we are probably in the correct area if that doesn't have 3.3 v with the TV on

[sansanpartida]

Turn the tester to max volts/amps like I said. When not touching anything it'll read 330 or something and then when you test each led strip it should give like 100 milliamps and 84.6 (or whatever voltage) across the board then. There will be 64 light strips to test.

If you were getting them to light up dimly you were doing it right.


Make sure that switch is NOT on 1ma, set it all to max.

Then like I said, move down each pin on each side as you were doing. BUT if you don't have the 3.3 V to led driver. That's probably the issue.


And as for your 1.4v drops when disconnecting, yes you did that test fine and maybe I was mistaken on my numbers. But I think we are probably in the correct area if that doesn't have 3.3 v with the TV on

OK, I was afraid of blowing the LED by putting the tester to 300V max Amp… I'll go to my parents' house in a few minutes and keep you updated.

So, to be sure, I'll do the test correctly:

Tester on max settings; positive leads to the center of the ribbon and negative to the 8 outermost pins and see if they turn on.

Is that right?

[EazyBone]

OK, I was afraid of blowing the LED by putting the tester to 300V max Amp… I'll go to my parents' house in a few minutes and keep you updated.

So, to be sure, I'll do the test correctly:

Tester on max settings; positive leads to the center of the ribbon and negative to the 8 outermost pins and see if they turn on.

Is that right?

Yea, however you got it to work last time. If you accidentally switch the terminals it just won't work. It shouldn't blow anything no. Yes they find the correct voltage to run through, they also supply like 120mv when then tv turned on will supply like 400mv or much more so it's gonna be fine.

Definitely test again, but it's looking like we still found something at the led driver board, or at least that was my problem before and looking like it could be yours also.

[sansanpartida]

Yea, however you got it to work last time. If you accidentally switch the terminals it just won't work. It shouldn't blow anything no. Yes they find the correct voltage to run through, they also supply like 120mv when then tv turned on will supply like 400mv or much more so it's gonna be fine.

Definitely test again, but it's looking like we still found something at the led driver board, or at least that was my problem before and looking like it could be yours also.

So far, I'm observing the tester voltage dropping from 300V to 90V each time I touch a connected LED on the ribbon. The light is really faint though. Is this expected behavior? I think I've checked the voltage drop along the entire ribbon but haven't double-checked the light on the other side of the TV each time. Should I verify the voltage drop with a light? My little orange assistant isn't much help, and it's hard to check the ribbon on the backside of the TV and confirm if the LED is on 😅

[EazyBone]

If you look through the back of the TV they will light up and can see the light through the holes. But if they all read the same number exactly then I wouldn't try and look at other side (never have). Only if any of them read any number then the exact number would I consider opening the TV up even. This thing is huge to me, so if you had to take the screen off I'd want to be sure.

Yes if all 64 tests at 90v then you are probably good on LEDs.