Vizio L32 No Backlight

[kevinm34232]

TV has normal standby and powers on, backlight flashes for a second then goes out. Can see video shining a flashlight on screen.
Get approx 5v to BLON then goes down.
Getting 24v to inverter VDD pins.
F101-105 test good.
T105 has a little residue by pin 1 where all others have a white dot.
Inverter board part # is AUO 19.26006.095

The specs for the 4005DXXXXXX(MS307T) transformers say:
The secondary resistance is about 0.8 K between S1 and S2 (or S3 and S4). The primary resistance is about 0.5 ohm between P1 and P2 (P3 and P4).

So I started checking with meter at 2k, not sure if I had the right pins for secondary but it's the only pins that gave me close to the specs:

T101 - .892 .888
T103- .896 .893
T105- .886 .886
T107- .889 .886
T109- .855 .885
T111- .879 .875
T113- .909 .909
T115- .873 .871

If I did that correct I see some deviations in T109 and T113.

Does it seem like an inverter board problem? I do not really have any way to test the lamps..

[kevinm34232]

Re: Vizio L32 No Backlight

I was able to get the backlight to come on by bypassing the protection just to see what screen looks like. As you can see the OSD is fine but there is the black marks/shadows going down the screen. What is that??!

Also as a side note, all of a sudden I noticed the power LED light went to green when plugging in, and unresponsive, instead of the normal yellow standby when plugging in. I figured something happened to the main board. Found an open 2A fuse on the main board on the 3.3v line, I musta hit something by mistake. Replaced it and back to where I was before..

[budm]

Re: Vizio L32 No Backlight

How did you bypass the protection?
T109 does not look right with 855 Ohms reading.

[kevinm34232]

Re: Vizio L32 No Backlight

I had run across this article on another TV:

http://www.bestelectronicarticles.co...ht-system.html

I looked up my inverter IC datasheet and was similar, just had to ground pin 1.
I figured it was worth a try to see what the backlights looked like or if screen was cracked..

That black smear though I'm not sure what's going on with that..?

[budm]

Re: Vizio L32 No Backlight

OK, I have done that one before, was not sure if your board uses the OZXXXX IC or not.
Thanks. That smear on the screen, was it there before? It is either contamination or some pressure was put on the screen to cause what you are seeing, not 100% sure.

[kevinm34232]

Re: Vizio L32 No Backlight

Well that's the thing I never saw the screen on before so not sure. I wasn't sure if that is a bulb issue or the panel. Wouldn't a bad bulb be a dark bar across the screen? Could whatever that is be causing the shutdown of the inverter? Those transformers are like $11 each on ebay, the whole board is around $50 which I don't want to do for this TV..

I also left it on for few minutes and none of the transformers felt warmer than any others..

[kevinm34232]

Re: Vizio L32 No Backlight

Someone had posted somewhere a Youtube link of bypassing individual transformers on a Samsung for a bad CCFL lamp when there was a transformer for each lamp, I think that may work here does anyone have that link?

[kevinm34232]

Re: Vizio L32 No Backlight

I found the video I was looking for:
http://www.youtube.com/watch?v=oE6K4...eature=related

However this inverter doesn't have the same type of feedback circuit.

Im trying to understand where the feedback signal is coming back from the lamps and where and how it's being interpreted on this board without a schematic.

I've read some info about unplugging a suspect lamp and connecting a good feedback signal from another lamp to that circuit to determine if bad lamp or inverter I just want to see if it will work..

[tom66]

Re: Vizio L32 No Backlight

That is mura. Unrepairable usually. Maybe if a bulb has split and burnt, it has burnt the inside of the panel??