Sony KDL-46NX720 possible purchase

[freakaftr8]

Re: Sony KDL-46NX720 possible purchase

Really to start id get dirty and diode test every single led

[tibimakai]

Re: Sony KDL-46NX720 possible purchase

I don't think that I have to go so far just yet, since the TV turns on and it shows the setup screen and then shuts off. Even if I will have to take that step, I guess I can see which one is bad.
I haven't taken the panel apart just yet. It doesn't even have a case, it has a Gorilla glass at the front. I have to be extra cautious with this, it's the first time working on a 3D TV of this caliber.

[freakaftr8]

Re: Sony KDL-46NX720 possible purchase

True. Unfortunately it's near impossible to test tge led banks as a whole. At least as far as a meter goes. Maybe an oscope.

[tibimakai]

Re: Sony KDL-46NX720 possible purchase

I have a scope. Can be tested with it?

[freakaftr8]

Re: Sony KDL-46NX720 possible purchase

Im not sure of the proceedure. Can you verify if the lamps are all lit the split second they come on? Look for dark areas.

[tibimakai]

Re: Sony KDL-46NX720 possible purchase

It actually stays on more, like 10-15 seconds.
It's hard to see a darker area. It could be only one bad LED.
On the LED driver board at the IC 5 (FAIL 5) the voltage is less then the other five ICs. Maybe that bank of the LEDs has a problem. Who knows which one is that.
I wait a little bit to see if anybody has any other ideas, and if nothing comes up, then I will take it apart.

[budm]

Re: Sony KDL-46NX720 possible purchase

Does the service explain how the LEDs are connected? Are there 4 strings? I want to suggest move the flat cable around and see if the fault reading will follow, but since I have no idea at this point on how those 4 flat cables are connected. I did not download that large service manual yet, I was hoping to find the training manual for this chassis but no luck yet.

[freakaftr8]

Re: Sony KDL-46NX720 possible purchase

I would only assume that each led strip would have a proprietary connection. But I could be wrong.

[tibimakai]

Re: Sony KDL-46NX720 possible purchase

This TV, is an edge lit LED TV, so I assume that there is a strip at each side of the TV.
There are four ribbon cables going to them from the driver board.
I don't understand why there are 6 ICs? The two horizontal strips are longer and require two ICs?

[budm]

Re: Sony KDL-46NX720 possible purchase

This is what I think, there are 4 connectors, each one of the connector has one of the pin connected to the 27V power source which will be connected to the Anode of the LEDs, the Cathode return lines as you can see, there are 24 of them for 24 strings (12 pads in each group). So that means each string will have about 8 LEDs. Those return lines are connected in series with 24 current sensing resistors for the constant current control feedback, these resistors will then be connected to the MOSFETs inside those 6 IC and then return to the 27v power supply ground. The EACH IC controls 4 return lines for the LED, 6 ICs x 4 current return lines = 24 LED STRINGS. Each connector handles 6 strings of LEDs.

[tibimakai]

Re: Sony KDL-46NX720 possible purchase

Nice! Most likely that is how is set up.
Where I have marked 0.395V (FAIL 5) is the lowest voltage. The other five test points, are 0.589V. That must indicate something it's bad, no?

[budm]

Re: Sony KDL-46NX720 possible purchase

Yes. So what you can do is to have one cable attach just one at a time, the backlights should come on and then goes into shutdown. May be you can see which one is not lit up. I have a feeling the one with 0.395V is the one that may have high string resistance so less current on the feedback resistor thus lower voltage reading. Need to find the spec of those 6 ICs.
How many of the 'FAILED' pads are there? 6 FAILED PADS, one per IC to monitor 4 strings of LEDs..

[tibimakai]

Re: Sony KDL-46NX720 possible purchase

Each IC has one. I will check now the ICs.

[tibimakai]

Re: Sony KDL-46NX720 possible purchase

It's a BD9276EFV.
It seems that the left edge it's darker as it lays down. Mostly the corners.

[tibimakai]

Re: Sony KDL-46NX720 possible purchase

OK, I took it apart and there are two long horizontal LED strips divided in two shorter strips.
2 x 48 on top and 2 x 48 at the bottom.
Now when I turn it on, all the LEDs light up and then the top and at the bottom the most right 16 LEDs dim and then the TV turns off.
I assume that the LD board is the problem.

[budm]

Re: Sony KDL-46NX720 possible purchase

So how are those 4 ribbon cables are attached to the LED strips?

[tibimakai]

Re: Sony KDL-46NX720 possible purchase

I haven't removed the sheets and the acrylic piece. Should I?

[budm]

Re: Sony KDL-46NX720 possible purchase

The reason I ask is that you should try switch the ribbon cables around from one socket to other to see if the symptom will follow.

[freakaftr8]

Re: Sony KDL-46NX720 possible purchase

probably to inspect if one led or more are dead on the strip.. Or can you visually see every single led right now?

[tibimakai]

Re: Sony KDL-46NX720 possible purchase

I don't see any dead ones.
16 LEDs from the corner, both up and down strips light up, really bright ad them they dim. The rest stay bright and then the TV Turns off.
I have tried doing at the LD board, but I couldn't connect one of them and then the TV did not want to turn on.
OK, I will remove them.