Sony KDL-55NX720 blinks 4 times

[beanboy33]

I have been searching for what the Sony blinking light 4 times code means.

The TV quickly shuts off after about 5 seconds of being powered on. The TV will blink 4 times in the lower left corner after automatically shutting off.

[beanboy33]

Re: Sony KDL-55NX720 blinks 4 times

Looking into it a little more, I think it may have something to do with the LED backlighting.

[tom66]

Re: Sony KDL-55NX720 blinks 4 times

I think 4 blinks is a backlight error so it may be LED related. How about some pictures of the boards in the set?

[CoppellTVRepair]

Re: Sony KDL-55NX720 blinks 4 times

Spent some time today troubleshooting a KDL-55NX720 with screen coming up for 4-5 seconds and then shutting off.

Haven't figured it out yet, partially because of Sony's idiotic design where if anything is disconnected (or failed) the whole TV shuts down and partially because, as usual, I was hacking and reverse-engineering my way around it without consulting any service manuals or schematics.

What I found today and what may help others in the unlikely event that I won't figure it out and the more likely that I don't publish it after I figure it:

4 blinks are clearly a code related to the back light.
There is a dedicated LED controller in this set and out of it there are 4 strips with 15 wires on each; of those 15 wires 4 are VCC for the LEDs on that strip and there are 6 or 8 individual wires - I think 6 - most likely for 6 individual LED circuits.

In other words the backlight is comprised of 4 * 6 = 24 LED circuits (or 4*8, sorry I did not remember) all driven by the controller.

If it was *me* designing this I would have made it so that if one of those 24 circuits fails the rest would continue working and TV may show an error or something.

I mean the whole beauty of having so many separate LED circuits is that you do have, actually, the luxury of continuing to operate even if you lose one of them; quality of backlight would drop, but barely noticeable.

However, if any of the 4 strip cables is disconnected in a *working* unit, the TV behavior is the exact same - it comes up for a short while and then shuts off.

Which lead me to believe there is a problem with one of the LED circuits after all.

Well I tested them all with a LED tester today and they all responded the same way; I did it twice and twice they all stopped the meter at 16V whereas if any of them had a burned LED it would have stopped it way higher, about 300V, just like any other open circuit.

Oddly enough, though, when operating on its own the LED controller outputs about 36V on those whereas my tester stopped at 16 and did not want to go higher; also I did not not see any of them actually lighting up , but that is to be expected considering the low voltage; the LED meter is still new device and I am not used to its quirks, but the mere fact that they all did the same 16V and neither was open to me is a solid indication the backlights are actually OK.

So the next logical step is the backlight controller.

it has big power going in and feedback from the T-CON, I guess for the sake of dynamic backlight.

If any of those cables is disconnected the result is the same - 4 blinks.

This means that if the T-CON may also cause, indirectly, 4 blinks error if for whatever reason the communication between it and the LED controller fails.

This is where I am after having spent about 30 minutes with it.

Hope it helps others.

[Packard93]

Re: Sony KDL-55NX720 blinks 4 times

try using a bright light on screen to see if a pic is there . if so backlight or inverter problem. You will need to test voltages inside cabinet to see . Do u have stby red or green power.

[RinusB]

Re: Sony KDL-55NX720 blinks 4 times

Dd you actually measure the individual tst points whl turning on the set? I measured 3.7v to 3.72v on all of them while starting for just a few seconds. After that they all dropped to 1.6v and a bit lower before the backlights turned off and the four blinks started.
The far right ribbon contacts 11 to 16 also started with 3.7v but went up to 10 v before it shut down.
It just may be one of the strips.

[budm]

Re: Sony KDL-55NX720 blinks 4 times

So far the OP never provides any pictures of the boards for us to see what we are dealing with.
Please attach good clear pictures of the whole backside of the TV showing all the boards and then good clear straight shots of the whole board of all the boards.
Use 'Go Advanced' to attach the pictures.