Vizio M421VT LED no display

[budm]

Re: Vizio M421VT LED no display

Those two caps are the primary side of the LED power supply.

[hienton2]

Re: Vizio M421VT LED no display

I think vled is about 145v. Check q601 q602 Fb601 next to Q601.
There are 2 more Qs on the other side of the board to run for producing vled.

[budm]

Re: Vizio M421VT LED no display

I do not think that the LEDs driving voltage is that high at all, you can see 12 MOSFETs for the 12-string LEDs. I see black blob on the IC, is that a blown top?
Q601, Q602 are for the PFC voltage booster circuit, if you are getting about 380vdc on the two 450vdc main caps, then the circuits are working.

[hienton2]

Re: Vizio M421VT LED no display

Hello budm.

I have a board for model PLDH-A954A : label input 100-240 ac
output 5.1v, 12v, 145v

[ryan74]

Re: Vizio M421VT LED no display

ok so VLed must not be getting any voltage.

324.5vdc on the 2 450v caps. should be good.

The blob on the ic looks like ink under 10x magnification.

Thanks

[budm]

Re: Vizio M421VT LED no display

I am tracing out the board to see how it is done, in the mean time, can you get the P/N on the ICs on the LED power supply board where the 12 MOSFETs are.
@hienton2: your board is not the same as this board, it is PLDF-001. I have to look further to see what voltage for driving the LED in this TV is.

[ryan74]

Re: Vizio M421VT LED no display

the larger one:
ae
AS3693B
1023VAA

smaller one: difficult to read, hope I got it right.
MEGA48FA
AU1C41

[ryan74]

Re: Vizio M421VT LED no display

I pulled the bridge rectifier after tracing Vled from CN902 and CN905 back to it.
I used this method on video for testing:
http://www.youtube.com/watch?feature...&v=dqkT6hF0O3E

If I tested it correctly it fails in one direction. see pics

I guess I will start by ordering 2

[tom66]

Re: Vizio M421VT LED no display

The 33u/200V are definitely on the cold side. 145V sounds plausible, but quite high! The use of the bridge rectifier is rare though, but it's possibly because the transformer is full bridge switched (which means it can be smaller, essential in thin LED set.)

[tom66]

Re: Vizio M421VT LED no display

That bridge reading is suspicious, looks like one diode drop across AC terminals, possibly there is a shorted diode inside it. Checked all pins for shorts?

[ryan74]

Re: Vizio M421VT LED no display

I have to call digikey for an alternate part unless someone can link a replacement.
Here is the datasheet for the bridge rectifier.
p/n:
ERS404M
VA34

Tom- I tested exactly as in video and only had a different result when testing across ac. one dirrection only like in pics.

[tom66]

Re: Vizio M421VT LED no display

So, testing the bridge: Looking at device from top label side pin 1 is +, 2 and 3 are ~ and 4 is -.

Meter probes in order (red) (black)
Pin 2 to 1 you should see ~0.4V
Pin 3 to 1 you should see ~0.4V
Pin 1 to 2 you should see OL
Pin 1 to 3 you should see OL
Pin 4 to 1 you should see ~0.4V
Pin 1 to 4 you should see OL
Pin 2 to 3 you should see OL
Pin 3 to 2 you should see OL

Good? Bad?

Any standard bridge e.g. GBU406 should work

[ryan74]

Re: Vizio M421VT LED no display

(R) (B) probes

Pin
2 to 1= .462v
3 to 1= .001v
1 to 2= .OL
1 to 3= .001v
4 to 1= .455v
1 to 4= .OL
2 to 3= .463v
3 to 2= .OL
Yeah it's bad

this should be good
http://www.digikey.com/product-detai...6DI-ND/1935033

[budm]

Re: Vizio M421VT LED no display

What DC voltage do you get at the 33uf 200V before pulling the bridge out? They are fed by the that bridge rectifier. I am surprise that it did not damage the two MOSFETS that drive the transformer.
It does look like it use high voltage for the LEDs, the MOSFETs may be in series with each strings for sinking the load which are the LEDs.
Looks like you narrow done the right parts. I am still tracing out the board.

[ryan74]

Re: Vizio M421VT LED no display

226mVdc. nothing
I dont get a volt reading on any of the 4 bridge rectifier pins either.

The left transformer(wrapped in yellow) that bridges hot and cold sides is cold to the touch.
Right one is warm

On this pic I marked where the 450v caps are and I had 324v.
also marked where it felt cold.

[budm]

Re: Vizio M421VT LED no display

We just have to wait until you get the new bridge installed then, good job finding it by the way.
But I do not understand how you get 10V at the other pins of the LED connectors.

[ryan74]

Re: Vizio M421VT LED no display

yeah this has been a pain for my first led.

I put bad rectifier back in when I updated post 35 with pic. I think theres more wrong with it. that voltage regulator?? is cold.

Update- pic shows what readings I got from hot and cold sides while connected.
p/n: 2NP000136DX-R
B FL 101208
I may need help finding its replacement also.

[budm]

Re: Vizio M421VT LED no display

I am surprised that your meter can read the AC voltage on those test points since that transformer is driven at 50KHz to 80 KHz range, most cheap meter does not have the bandwidth to measure those high frequency on that switching power supply transformer.
I would wait for the new rectifier first.

[budm]

Re: Vizio M421VT LED no display

AS3693B LED BACKLIGHTS controller:

MEGA48FA is the micro controller: Notes: not 100% sure
https://cdn.badcaps-static.com/pdfs/...e5441e060e.pdf
From the way it looks from the IC spec of the LEDs driver IC, I think once the bridge rectifier is replaced to get the voltage for the LEDs you will be OK unless the circuts that drive the transformer also failed due to shorted out bridge.

[tom66]

Re: Vizio M421VT LED no display

(R) (B) probes

Pin
2 to 1= .462v
3 to 1= .001v
1 to 2= .OL
1 to 3= .001v
4 to 1= .455v
1 to 4= .OL
2 to 3= .463v
3 to 2= .OL
Yeah it's bad

this should be good
http://www.digikey.com/product-detai...6DI-ND/1935033

Why you sad? You just found the failed part!

The bridge acts like a short across the SMPS transformer, so I'd expect the SMPS on there to simply go into protection mode. No damage done.