Vizio XVT553SV Powers up/audio/no vid.

[Bob-62]

Re: Vizio XVT553SV Powers up/audio/no vid.

No it was unpluged for continuity test.

[budm]

Re: Vizio XVT553SV Powers up/audio/no vid.

So what is the diode readings on the transistor?
And also recheck the voltages on all 3 pins again to make sure nothing is damaged

[Bob-62]

Re: Vizio XVT553SV Powers up/audio/no vid.

looks like i may be at a stand still at this point.
tryed testing the transistor, get a readind for a second then nothing.
my luck looks like i borrowed a bad meater

[budm]

Re: Vizio XVT553SV Powers up/audio/no vid.

If we cannot depend on the correct reading from the meter, then all our previous testings will become invalid.

[Bob-62]

Re: Vizio XVT553SV Powers up/audio/no vid.

looks like nothing was damaged. backlight still comes on. voltage still the same.
as afr as the meter goes, i checked resistance against some resistors seems to be ok. also checked voltage against 1.5 v battery & 9 V battery seems to be ok. but on diode scale
a 1 appears on display then when i touch the pin 3 didgets flash on display .
is it possable only the one function is not working?

[Bob-62]

Re: Vizio XVT553SV Powers up/audio/no vid.

Might i not be getting a good read because it is in a circuit?

[budm]

Re: Vizio XVT553SV Powers up/audio/no vid.

I would say, go out and spend about $50 on a new meter otherwise I will be spending hours try to figure out if your meter is good or not.
And lets say that the transistor is bad, can you do surface mounted repair and you have the proper tools?

[Bob-62]

Re: Vizio XVT553SV Powers up/audio/no vid.

I have a good meter. its just 50 miles away on the jobsite. wasnt expecting to need it on my days off. so i left it at work.
And if it is the transistor , yes i have the proper tools & have in the past done surface mounted repairs.

[Bob-62]

Re: Vizio XVT553SV Powers up/audio/no vid.

looks like i will have to pick this up after the hollidays.
I thank you so much for your assistance.
Looking forward to talking to you when i get all my tools rounded up.
Take care & have the most happiest hollidays.

[budm]

Re: Vizio XVT553SV Powers up/audio/no vid.

As you can see from troubleshooting, if that is the correct transistor, that transistor should be on and the 12v should appear at the Collector to supply the voltage to the T-CON, just a matter of finding out if the transistor is good or not. The Base voltage should change when the TV is OFF and when the TV is ON.

[rbwilcox811]

Re: Vizio XVT553SV Powers up/audio/no vid.

Budm or Bob-62, Did you ever get your Vizio to work? I have the same problem with mine, (just started going blank) (purchased in 1/2011). If you ever got back together to finish troubleshooting, I'd love to hear what you found was bad. Thanks!!

[jdboeck]

Re: Vizio XVT553SV Powers up/audio/no vid.

Just chiming in here... hopefully this will help Bob and rbwilcox, along with myself...

Q3 is not a transistor, it's a SCR. So, based on this info, substituting the proper nomenclature:

Bob's readings:
On Q3
Drain .32
Source 12.16
Gate 10.85

The SCR should be "on", thus outputting 12V to the main board. Since it is not, the SCR is defective. I am about to try and locate one and replace mine, as I have the exact same problem.

[jdboeck]

Re: Vizio XVT553SV Powers up/audio/no vid.

*** CORRECTION ***

For some reason I typed SCR when I meant to type FET (mosfet)

so, Q3 is a MOSFET, not SCR

sorry about the confusion

[jdboeck]

Re: Vizio XVT553SV Powers up/audio/no vid.

I did this for my repair. I used an NTE 66 MosFET transistor and pigtailed it to the pads where the original 3403 SMT MosFET was attached, used insulating pad and bushing to attach it to the circuit board's existing mounting lug. So far, so good! My tv is back up and running!

I attached a photo of my repair for all to copy

[budm]

Re: Vizio XVT553SV Powers up/audio/no vid.

"On Q3
Drain .32 This is the output pin
Source 12.16 The B+ is fed to this pin
Gate 10.85"
The NTE66 is the N-Channel MOSFET, the Source then should not be connected to the B+, right now the B+ forcing the current to flow through the body Diode of the MOSFET. You cam verify if the MOSFET is switching on and off or not by disconnecting the Gate.

[Sal44]

Re: Vizio XVT553SV Powers up/audio/no vid.

jdboeck, I know this is an old thread but I was wondering if the NTE66 mosfet held up? Did it ultimately solve the problem?

[budm]

Re: Vizio XVT553SV Powers up/audio/no vid.

I am sure it is still working because the MOSFET does not turn off since the replacement is N-CH instead of the original P-CH which might as well put the diode in its place and the 12V at the Drain will always be there instead of being shut down when it is needed too.

[Sal44]

Re: Vizio XVT553SV Powers up/audio/no vid.

So which method is better using the N-CH mosfet pigtailed or using the 20k or 100 ohm resistor to ground the gate? I've seen in reading through the threads they both seem to work.

[mscserbia]

Re: Vizio XVT553SV Powers up/audio/no vid.

Wow,that looks like an alternator

[budm]

Re: Vizio XVT553SV Powers up/audio/no vid.

The MOSFET is being used as a switch, when the wrong type is put in, the body diode will allow the current to flow all the time so the MOSFET does not do anything which you might as well bypass the MOSFET if you want to use N-CH MOSFET. The correct part is the P-CH MOSFET, but you need to find out first if the MOSFET is bad or the GATE drive signal is bad.