Vizio 42" LED TV No backlight, blows fuse

[Sparkey]

Hi;

This is a Vizio M420NV.
Backlight was out, I found an open 3A fuse (TF1) on the main board that carries 12.4 vdc. When fuse replaced, the backlight will flash a couple of times and poof goes the fuse again.

I don't have a diagram. I wonder if this might be due to a inverter fault ?
I checked power transistors on main and power supply board.
Any ideas ?

Thanks,

 

[N_Cook]

Sparkey <wwspage@aol.com> wrote in message
news:69088ccd-8227-4828-aa6b-e36613b62d4e@googlegroups.com...

Hi;

This is a Vizio M420NV.
Backlight was out, I found an open 3A fuse (TF1) on the main board that
carries 12.4 vdc. When fuse replaced, the backlight will flash a couple of

times and poof goes the fuse again.

I don't have a diagram. I wonder if this might be due to a inverter fault
?
I checked power transistors on main and power supply board.
Any ideas ?

Thanks,

Can you hear any fizzing/arcing across turns in the inverter Tx ?
Can you reduce the mains voltage a bit and maybe increase the amount of
on-time a bit , to monitor the fault situation a bit longer.

 

[John-Del]

On Tuesday, March 5, 2013 8:13:58 AM UTC-5, Sparkey wrote:

Hi;



This is a Vizio M420NV.

Backlight was out, I found an open 3A fuse (TF1) on the main board that carries 12.4 vdc. When fuse replaced, the backlight will flash a couple of times and poof goes the fuse again.



I don't have a diagram. I wonder if this might be due to a inverter fault ?

I checked power transistors on main and power supply board.

Any ideas ?



Thanks,

The fuse for the 12V feed to the main does not cover the inverter B+, that's fed directly from the smps to the inverter board(s) and fused at that end.. The inverter was blinking because the main is gimpy..

If the 12V fuse on the main is opening, you most likely have a shorted regulator IC on the main, and possibly an IC after that drawing and overheating the regulator. Unfortunately, Vizio is loathe to provide any service information on their boards. You're best bet at this point is to replace the main. Make sure you get the correct one as there are typically several versions for the same model to match the display\tcon.

 

[Sparkey]

The fuse for the 12V feed to the main does not cover the inverter B+,

Ahhh, that's what I wanted to know...

I needed to confirm that the inverter was not powered from main board.
So my problem is likely localized to the main board.
I will have another look at the power transistors and IC's tomorrow.

Thank you !!



On Tuesday, March 5, 2013 2:30:33 PM UTC-8, John-Del wrote:

On Tuesday, March 5, 2013 8:13:58 AM UTC-5, Sparkey wrote:

Hi;







This is a Vizio M420NV.



Backlight was out, I found an open 3A fuse (TF1) on the main board that carries 12.4 vdc. When fuse replaced, the backlight will flash a couple of times and poof goes the fuse again.







I don't have a diagram. I wonder if this might be due to a inverter fault ?



I checked power transistors on main and power supply board.



Any ideas ?







Thanks,



The fuse for the 12V feed to the main does not cover the inverter B+, that's fed directly from the smps to the inverter board(s) and fused at that end. The inverter was blinking because the main is gimpy..



If the 12V fuse on the main is opening, you most likely have a shorted regulator IC on the main, and possibly an IC after that drawing and overheating the regulator. Unfortunately, Vizio is loathe to provide any service information on their boards. You're best bet at this point is to replace the main. Make sure you get the correct one as there are typically several versions for the same model to match the display\tcon.

 

[Sparkey]

Tomorrow I will try to dial down the power a bit and see if the invert xformers fizzle with a new fuse...

Thanks

On Tuesday, March 5, 2013 7:34:53 AM UTC-8, N_Cook wrote:

Sparkey <wwspage@aol.com> wrote in message

news:69088ccd-8227-4828-aa6b-e36613b62d4e@googlegroups.com...

Hi;



This is a Vizio M420NV.

Backlight was out, I found an open 3A fuse (TF1) on the main board that

carries 12.4 vdc. When fuse replaced, the backlight will flash a couple of

times and poof goes the fuse again.



I don't have a diagram. I wonder if this might be due to a inverter fault

?

I checked power transistors on main and power supply board.

Any ideas ?



Thanks,

I



Can you hear any fizzing/arcing across turns in the inverter Tx ?

Can you reduce the mains voltage a bit and maybe increase the amount of

on-time a bit , to monitor the fault situation a bit longer.

 

On Tuesday, 5 March 2013 13:13:58 UTC, Sparkey wrote:

Hi;



This is a Vizio M420NV.

Backlight was out, I found an open 3A fuse (TF1) on the main board that carries 12.4 vdc. When fuse replaced, the backlight will flash a couple of times and poof goes the fuse again.



I don't have a diagram. I wonder if this might be due to a inverter fault ?

I checked power transistors on main and power supply board.

Any ideas ?



Thanks,

Hi there, I would also check any electrolytic capacitors on the inverter board, making sure they are at least 105 degree celcius type with low equivalent series resistance - low ESR type.