Vizio LED Backlight Issue? Dark areas

[roundbox52]

I just replaced the main board on my 50" Vizio LED, M502i-b1 which fixed my original issues. I now have an issue with dark areas on the screen, see picture. The image fills the entire screen it is just darker in some areas than others, like the lower right, lower left, center top...

I do recall when diagnosing the main board issue I created a spark on the main board at the power supply connector. This did cause the backlight to flash and partially remain on.

Any help on diagnosing this issue?

[jjanssen7]

Re: Vizio LED Backlight Issue? Dark areas

Is your main board an exact replacement? I had a very similar issue when replacing a main board with a similar (though not exact) replacement on that model.

[roundbox52]

Re: Vizio LED Backlight Issue? Dark areas

Is your main board an exact replacement? I had a very similar issue when replacing a main board with a similar (though not exact) replacement on that model.

Yes it is the exact # as the previous board. Did a different board solve you're issue?

[roundbox52]

Re: Vizio LED Backlight Issue? Dark areas

Before diagnosing the main board issue I don't recall having back lights, however once I created a short on the 1 & 3 pin of cn701 of the main board, the upper left back lights came on but no others. I'm wondering if I sent too much voltage to those leds somehow and they remained on or at least brighter than normal.

I'm thinking instead of having dark spots I really have bright spots. Would any of this make logical sense?

This picture is from tonight after turning the tv on. Typically, when everything is working as it should, I would have an almost black screen. You can see how some spots are bright.

[attainteddragon]

Re: Vizio LED Backlight Issue? Dark areas

on the connector that powers the backlights (i can't read the connection number, but it has the 4x red and black wires coming from it), can you check the voltage on all pins as it is powered on and what the voltage settles too and report your results thanks.

[roundbox52]

Re: Vizio LED Backlight Issue? Dark areas

on the connector that powers the backlights (i can't read the connection number, but it has the 4x red and black wires coming from it), can you check the voltage on all pins as it is powered on and what the voltage settles too and report your results thanks.

I measured the voltages at the cn804 on the driver board, not the psu.

Pin# / On / Settled

1 / 20.11 / 19.49
2 / 19.99 / 19.48
3 / 20.15 / 19.48
4 / 19.99 / 19.48
5 / .7mv / .4mv
6 / .7mv / .4mv
7 / .7mv / .4mv
8 / .7mv / .4mv

[roundbox52]

Re: Vizio LED Backlight Issue? Dark areas

Anyone?

Anyone know what is going on or what I should check next?

[attainteddragon]

Re: Vizio LED Backlight Issue? Dark areas

my bad, i didn't see the separate driver board. can you do the same thing for connector cn801 and cn802.

[roundbox52]

Re: Vizio LED Backlight Issue? Dark areas

cn801
Pin# / On / Settled

1 / 19.69 / 30.07
2 / 19.75 / 30.08
3 / 19.71 / 30.09
4 / 19.75 / 30.09
5 not used
6 not used
7 / 11.15 / .607
8 / 11.44 / 11.49
9 / 10.95 / 11.26
10 / 11.49 / 11.49
11 / 11.65 / 11.35
12 / 11.65 / 11.62
13 / 10.80 / 11.36
14 / 11.37 / 11.41
15 / 11.44 / 11.46
16 / 11.36 / 11.41
17 / 11.36 / 11.38
18/ 11.52 / 11.54
19 / 11.42 / 11.43
20 / 11.46 / 11.48
21 / 11.45 / 11.48
22 / 11.43 / 11.44
23 not used
24 not used

cn802
Pin# / On / Settled

1 / 19.77 / 30.11
2 / 19.77 / 30.12
3 / 19.74 / 30.12
4 / 19.77 / 30.12
5 not used
6 not used
7 / 2.5 / .742
8 / 9.4 / 11.56
9 / 8.9 / 10.48
10 / 11.1 / 8.53
11 / 5.3 / 3.93
12 / 11.2 / 11.67
13 / 2.4 / .762
14 / 8.9 / 11.33
15 / 2.2 / .605
16 / 10.9 / 11.37
17 / 9.4 / 7.69
18 / 11.36 / 11.39
19 / 11.12 / 10.88
20 / 10.76 / 10.75
21 / 11.28 / 10.93
22 / 11.45 / 11.54
23 not used
24 not used

Something seems goofy with some voltages on cn802 when compared to cn801 and even #7 on cn801. Not really sure what the driver board does or if these numbers indicate an issue.

[budm]

Re: Vizio LED Backlight Issue? Dark areas

https://www.badcaps.net/forum/attach...8&d=1503842055
It looks like you have some open circuits in the LED strings. You have 16 LED strings. (http://www.shopjimmy.com/vizio-lbm50...-16-strips.htm)
What are the P/N of Q801, U801?

[roundbox52]

Re: Vizio LED Backlight Issue? Dark areas

What are the P/N of Q801, U801?

Sorry for my ignorance but is P/N stand for Possitive/Negative?

I found Q801 (which has test points labeled 1-7) and U801, but would be unsure of how to test U801. Any chance you can elaborate on what I should be checking?

[mmischni]

Re: Vizio LED Backlight Issue? Dark areas

P/N in this case is Part Number of those components. What numbers are printed on them?

[budm]

Re: Vizio LED Backlight Issue? Dark areas

P/N in this case is Part Number of those components. What numbers are printed on them?

Yes.

[roundbox52]

Re: Vizio LED Backlight Issue? Dark areas

Great. See attached photos for part numbers.

Are we thinking these two components are bad and giving poor voltage to some of the leds?

[budm]

Re: Vizio LED Backlight Issue? Dark areas

Right now we are looking to see how those LEDs are being driven.
Dual MOSFET AO4892.
16 channel LED driver/controller AS3820.
Probing the IC and the MOSFETs Voltages are to be done next to verify if we have bad LED for sure or LED driver problem. Taking panel apart is the last thing you will want to do.
So far it looks like you have 32 set of LEDs not 16 as first thought.

[budm]

Re: Vizio LED Backlight Issue? Dark areas

BTW, what is the model number of the LCD panel?
TPT500J1-HVN08????

[roundbox52]

Re: Vizio LED Backlight Issue? Dark areas

I think the LCD panel is 705TXES235200X, see picture.

Let me know what to probe and if it is anymore difficult than just getting dc voltage.

[budm]

Re: Vizio LED Backlight Issue? Dark areas

So far no luck finding info for the LCD panel. It does look like you have do have LED problem.
You can take a chance on replacing the LED driver board for $15:
http://www.shopjimmy.com/vizio-lntve...ed-driver.htm#
I would get a LED tester similar to this:
http://www.shopjimmy.com/sid-gj2c-le...ght-tester.htm