Vizio SV420XVT1A LCD 2 Seconds to Black

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

It looks like it goes to a ZD202 on the top. So i should be able to test the one side of the diode to check the VCC.

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

Uploaded photos, bottom shot is a little blurry but the concept is there

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

So i found this page for IC fan7602

https://cdn.badcaps-static.com/pdfs/...02ce845453.pdf

[budm]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

OK I looked real close at the traces, it looks like the FAN7602 is not used for driving the inverter circuits.
Please see PDF attached

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

Here is the info off IC 301:
MSC
LX16921DW
0844C

[budm]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

OK, I found the Data sheet, it is the CCFL Controller, LX16921DW

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

Sweet thanks I will look it over and see if I can make sense of the document

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

OK I looked real close at the traces, it looks like the FAN7602 is not used for driving the inverter circuits.
Please see PDF attached

So I will test the Mosfets now should i test the gate transformer as well?

[budm]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

More likely to be OK since the backlights did flash on then go black. That IC has circuits that sense over current draw by the CCFL, or it sense that the CCFL's fired up but did not stay lit (conducting) so those two condition will cause the inverter to go to shutdown mode, or the IC itself may be bad. There are lots of parts in that section. We need to verify if we do have the VDDP (Power supply pin for the IC) and the Enable pin pin 6.

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

I just tested the MOSFEts and here are the results:
Top
S-G MM set at 20k its 9.07
MM set at 20M
S-D: climbs out of range
D-G: climbs out of range
Bottom
S-G MM set at 20k its 9.01
MM set at 20M
S-D: climbs out of range
D-G: climbs out of range

[budm]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

OK, they are good. The DC voltage checking of the CCFL controller IC which is in the cold side of the power supply, you can use the chassis as the ground point. You should download the PDF I attached.

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

Just tested the brown cap too which climbed out of range as well

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

So I will need to test Pin 1 and pin 6 on the IC 301. It looks like pin 1 can be tested with J16 on the top does that look correct? But dont know how to test pin 6 from the top any ideas?

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

Just tested J16 and it was at 5.01Vdc, if i am reading the document you pointed me to that seems high, that is if J16 actually is the top connection of VDDA. Document says 4.2V max, am I reading that right?

[budm]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

Pin 1 is VDDA, 4.2V max, VDDP PIN 20 is 5.5v max. The black meter probe will be on the chassis, the red probe will be for reading pin 1, pin 20, pin 6. I am not sure what J1 is. If pin 1 (output voltage VDDA) is 5v thenit sound like the LDO (Low Drop Out) regulator inside the IC is bad.

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

I will try and figure out how to power board upside down to test pins.

[budm]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

They do not make it easy since you do not have the extension cable set like the factory or the service tech has for bench repair.
Have you shop around to see how much the replacement board is?

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

Yeah I could get it for 109 plus core. I was thinking about buying to just test.

[budm]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

That is a lot.

[Crimsonmt]

Re: Vizio SV420XVT1A LCD 2 Seconds to Black

Yeah I know