Vizio - XVT472SV

[budm]

Re: Vizio - XVT472SV

If you check the resistance between the fuse on the T-CON board and one of these two MOSFET's leg/s, one of them should show <1 Ohms between the fuse and the legs of the MOSFET. Please verify which one, U1 or U33?

[jasenpeters]

Re: Vizio - XVT472SV

Guess who?

U33

If the diagram on the datasheet matches correctly, that would be the Drain Pins (5,6,7,8)
are connected to that fuse. (I could be wrong)

[budm]

Re: Vizio - XVT472SV

If it is the P-CH MOSFET then that will be correct that the fuse is connected to the Drain pin, the 12V is then should be connected to the Source, so check the DCV on the Source pin, it should have 12VDC there.
Then also check the Gate pin and tell me what you have, all the readings are ref to GND.

[jasenpeters]

Re: Vizio - XVT472SV

U33 - 4953GM
P-CH MOSFET Pin Voltages

Pin 1 (Source 1) = 12.09
Pin 2 (Gate 1) = 11.97
Pin 3 (Source 2) = 12.09
Pin 4 (Gate 2) = 11.97

Pin 5 (Drain 2) = 0.25
Pin 6 (Drain 2) = 0.25
Pin 7 (Drain 1) = 0.25
Pin 8 (Drain 1) = 0.25

Are the Gates getting sufficient voltage to "turn on" the MOSFET's?

[budm]

Re: Vizio - XVT472SV

The MOSFET is NOT being told to turn on, the Gate Voltage should be at least 1V less than the Source pin for it to start conducting, so the GATE pins should be 11VDC or LESS for it to be on.
So the turn on command from the processor on the main board is not working. If you connect 500~1K resistor (1/4W will be fine) between the GND and the GATE pins then you should have 12V output at the Drain pins.
Are pin 2 and pin 4 connected together?

[jasenpeters]

Re: Vizio - XVT472SV

On U33, pin 2 and 4 are connected via the land line. It's visible in the picture.
If I connect the resistor as instructed and the Drains go to 12v, then what?

[budm]

Re: Vizio - XVT472SV

If other functions of the main board are OK then you should see images on the screen since now you will have 12VDC feeding the T-con board for it to run.

[jasenpeters]

Re: Vizio - XVT472SV

I haven't tested it yet with a resistor. But, if the Drains go to 12 and screen shows images, can I use the resistor as a "fix", or should I replace the Main Board? (Assuming I can't replace the processor, or is this a software issue?)

[jasenpeters]

Re: Vizio - XVT472SV

Ok, I tested it.

I'm getting an image now: "No Signal"

So, since the MOSFET stays on after jumping with the resistor, could I "rig" up a switch to turn on the MOSFET as a temporary solution?

[jasenpeters]

Re: Vizio - XVT472SV

Now I'm testing inputs, channels, sound and features.
BTW, this TV was being thrown out, it was not mine originally.

[budm]

Re: Vizio - XVT472SV

"So, since the MOSFET stays on after jumping with the resistor, could I "rig" up a switch to turn on the MOSFET as a temporary solution?" Yes, but you must turn on the switch A COUPLE SECONDS AFTER the power switch is activated.
What can be done too is to use the BL-ON signal to feed inverter (simple common Emitter) circuit to turn on the MOSFET.

[jasenpeters]

Re: Vizio - XVT472SV

Every thing seems to be working now.

Do you recommend replacing the Main Board as a permanent fix, or can this "ON" signal fail be further troubleshooted? Is it software, perhaps?

[budm]

Re: Vizio - XVT472SV

All other functions are OK so it is not likely to be firmware problem.
You can try tracing the Gate connections to see where it goes may be there are broken traces or something.
If the main board is cheap around $50 or so it may be worth it. You can try running it as is to see if something else will fail later on.

[jasenpeters]

Re: Vizio - XVT472SV

I turned if off for about 10 sec, and turned it back on.
I get an image still. Could this be from charged capacitors helping the processor send the signal or something?

I'll try turning it off for much longer and see. It may be an intermittent issue.

[jasenpeters]

Re: Vizio - XVT472SV

Anyone have a schematic to this one? or at least this Main Board?
It makes tracing easier

[jasenpeters]

Re: Vizio - XVT472SV

I turned it off for over 24 hours, no power at all.
Still comes on, behaving normally.
All I can do is wait for it to misbehave again.

Any comments on why it failed originally?

I now have a new LCD TV upgrade (from a 36" tube boat anchor).
Hopefully it will last for a good while.

Thanks for all the help, I hope I can pay it forward.

[budm]

Re: Vizio - XVT472SV

Just keep an eye on it.

[dick_barton]

Re: Vizio - XVT472SV

As you have probably gathered in the uk we cant click on your links as shopjimmys banned us from seeing them. we have to use a web proxy

Hi Vinceroger69,
Why did they do that?

[vinceroger69]

Re: Vizio - XVT472SV

High fraud rates this thread has the emails i got back from them
https://www.badcaps.net/forum/showth...cess+shopjimmy

[dick_barton]

Re: Vizio - XVT472SV

Hello vinceroger69
Thanks for the update.
Regards