AOC E970SW no backlight

[Sraros]

I have this monitor which has backlight issues.
I can see image with flashlight, but the LEDS don't turn on.
The LED bar is working fine because when I unplug the monitor they flash altogether, every single one of them.
I don't have voltage on the output of the LED bar connector (with or without the bar connected) but I have 18,3V on the PSU to main cables.
The image on the panel works fine. Any ideas?

[nomoresonys]

Re: AOC E970SW no backlight

Check all the diodes, easy place to start.

[dick_barton]

Re: AOC E970SW no backlight

Some of your solder joints look cracked and need to be resoldered.

[dick_barton]

Re: AOC E970SW no backlight

Normally if the leds flash then there is a possibility that you have one or more leds shorted.
Check Q801 and D801. There sholuld be 15V on Pin1 of U801 and approximately 5V on Pin 5 of U801.

It would be worth checking all the 0 ohm resistors around U801

[Sraros]

Re: AOC E970SW no backlight

Pin 1 is 0,35V and Pin 5 1,5V.
All 0Ω resistances look fine and well soldered.
I am attaching a picture just to see if I measure the correct pins
Red arrow is pin1 yellow is Pin5
So should I assume U801 has gone bad?

[dick_barton]

Re: AOC E970SW no backlight

Sorry the 15V should be on Pin 9 not Pin 1 as I said above.
Pin 5 at 1.5V seems a little low. Can you check it agai but this time at the connector CN902.

Did you use you meter to test the 0 ohm resistors and Q801 and D801 ?

[Sraros]

Re: AOC E970SW no backlight

The 0Ω resistors I checked them all both in continuity and Ω. Look fine.
Q801 is G to D and S to D 18,sth with a small voltage difference between them.
D801 doesnt exist but I guess you mean D802 which is also ok. 18,4V with a 0,sth voltage drop.
PIN9 on the U801 takes 18,4V, PIN 4 3V which is the DIM from the main I guess? (Goes to 0 when goes into standby) and then PIN2,5,6,7,8 all have 0V.
CN902: Ground to white cable is 18,4, ground to black lead is 0V
I hope I gave all info as better as possible

[Sraros]

Re: AOC E970SW no backlight

By the way, I made a slow motion video of how the led bad reacts sometimes when I plug off the power cable without turning off the monitor. I upload a SS if it helps. To me it seems all LEDs are flashing, but I cannot say if this really means the bar is ok :/
Thanks for your help one more time

[dick_barton]

Re: AOC E970SW no backlight

Q801 is G to D and S to D 18,sth with a small voltage difference between them.

With the set off and your meter set to diode mode check Q801 and D802

Pin 9 at 18.4V is fine and is the Vcc supply for U801

What is the voltage between the pin marked ON/OFF to chassis when powered up and also on the DIM Pin.

Has the set only a single led bar as in post #8

Can you post the slow motion video you took of the leds

You do have some poor solder joints on the power supply that need to be resoldered.

[Sraros]

Re: AOC E970SW no backlight

ON/OFF is 1,6V when on and 0V when off.
D802 looks fine, in diode test 316 and no connectivity in reverse.
In diode test:
Q801: red S - black G:696, opposite no connectivity
Black D - red S:330
All the rest no connectivity

[dick_barton]

Re: AOC E970SW no backlight

What is the part number on Q801

Meter in diode mode

D - S = 0.33  and reverse leads S - D = Infinity
D - G =    and reverse leads D - G =
G - S = 0.69  and reverse leads G - S = infinity

What is the full board number 715Gxxxxxx

[Sraros]

Re: AOC E970SW no backlight

PA110BDA

D - S = 0.33 and reverse leads S - D = Infinity
D - G = infinity and reverse leads D - G = infinity
G - S = 0.69 and reverse leads G - S = infinity

[dick_barton]

Re: AOC E970SW no backlight

Mosfet appears to be OK.

Have you made good the poor solder joints around the board.

If you step by step your video can you see if any of the leds are not coming on or coming on later than the others

[Sraros]

Re: AOC E970SW no backlight

Can you tell by the video? I think there's a flow but looks normal

[dick_barton]

Re: AOC E970SW no backlight

Doing a video and stepping it has worked for many people on this forum.

[Sraros]

Re: AOC E970SW no backlight

It wasn’t uploaded, I had to zip it

[dick_barton]

Re: AOC E970SW no backlight

You said that when you powered down the led bar would flash. That's what the video should show.
Do you have an oscilloscope? It makes fault finding alot easier.

[Sraros]

Re: AOC E970SW no backlight

At the video I am unplugging the cord. The bar doesnt flash when I turn it off by the button, only when I unplug the cord while it’s ON.
Oscilloscope no, I don’t have :/ I am an amateur hobbyist

After the troubleshooting on the board, do you believe it’s the LED bar or the board?

[dick_barton]

Re: AOC E970SW no backlight

It's hard to tell at the moment. It may well be a problem with the Led driver IC or be the result of just one led failing.

Can you post the video of when you unplug the power and the led strip flashes. It does need to be well focussed on the strip.

[Sraros]

Re: AOC E970SW no backlight

Would it help to check in diode mode each LED separately?
From the last video though, if I freeze it right before they go full lit, it seems they work fine