Vizio SV370XVT turns on won't turn off no video

[kevinm34232]

First time I turned this set on, Vizio logo went from orange to white, backlight came on, I then saw Vizio logo come up on screen and go away quickly and then nothing. Backlight still on but no video.

From then on backlight came on but no video. Took it apart to check voltages now backlight not coming on either. All voltages are good and fuses on t-con, main board and inverter boards good. DC-DC voltages all tested where they should except for CE82 which was low.

Oh, also once set comes on, will not shut off. Remember Vizio having this issue before with voltage regulators on the main board I think. Service manual is not great... Anyone have experience with this, seems like a main board issue to me...

[tibimakai]

Re: Vizio SV370XVT turns on won't turn off no video

I would measure all the regulators on the mainboard.

[kevinm34232]

Re: Vizio SV370XVT turns on won't turn off no video

I measured all referenced in the SM, all seems good. Not sure what is going on. The fact that all voltages are good at inverter boards but now no backlight seems to indicate the main board wouldn't it? There are 3 pins coming from main board to PS board, and PS board to inverter board, labeled A, B and C. No voltage on those. As with the older Vizio I worked on, the available SM has no schematics just some basic troubleshooting. There is a more complete SM I found for the older one, but it wasn't easy to find.

[kevinm34232]

Re: Vizio SV370XVT turns on won't turn off no video

Picked up a new main board for this TV knowing the history of the main board issues.. Set fired right up..

So now my with curiousity as to what's wrong with the old board and the lack of info in the SM, I decided to compare voltages...

The only voltage is the SM that wasn't right originally was CE82, should be about 1.08v and was 0.6v on the old board. The new board is 1.1v. And....

NEW--------------OLD
U12 pins 5-8 = 3.4v ---------------U12 p 5,6,8 = 3.4v, p7 =0v
Q8 = 3.4v-------------------------Q8=0v (seems to trace to p7 on U12)
U8 = SAME
U1 = SAME
U2 = SAME
U9 = SAME
U4 = SAME
FB75 = SAME
Q10 = 0.2V--------------------------Q10 = 0.02V
U33 = P 1,3,5,6,7,8=11.8v,p2,4=0v----U33 = P 1,3=11.9v, p 2,4=11.6v, p5-8=0v
U14 = SAME
U6 = SAME

Obvious issues at U12 and U33.
U12 having 0v at pin 7 which seems to lead to collector of Q8 which is also 0v.
U33 has about 12v on all pins except 2 and 4 on good board, and 0v on pins 5-8 on bad board..

[kevinm34232]

Re: Vizio SV370XVT turns on won't turn off no video

Can anyone comment on whether it looks like these 2 components are bad or something else?

[selldoor]

Re: Vizio SV370XVT turns on won't turn off no video

The numbers are meaningless without the part numbers and data sheets
post them and you might get a bit more interest.

[kevinm34232]

Re: Vizio SV370XVT turns on won't turn off no video

I am looking for a complete SM.. I figured a comparison against a working board would help in the mean time.

[selldoor]

Re: Vizio SV370XVT turns on won't turn off no video

I am looking for a complete SM.. I figured a comparison against a working board would help in the mean time.

I doubt if you will find one - if you get the part numbers and data sheets as well as seeing if the output is within spec, they sometimes have circuit diagrams showing
suggested usage which may lead to finding if the part is at fault or something
connected to it is faulty. Have you checked if the part numbers are the same
on the parts you query on each board? Thay may have been swapped out .

[kevinm34232]

Re: Vizio SV370XVT turns on won't turn off no video

I think this is U33
http://pdf1.alldatasheet.com/datashe...4953GM_08.html

[cadiman]

Re: Vizio SV370XVT turns on won't turn off no video

You need to find the 3.3 volt regulators. They look like small transisters. (smt) surface mount.

The upper tab is the same as the middle leg. v in and v out. The input v might be 5 volts or more. If reading less than 3.3 the regulator is bad (2.7) would be bad they fail low as to not ruin anything on the board. This 3.3 volts dc is for processor logic. all mainboards use this and they fail all the time.

Test audio also. The audio circuit uses 12volts dc most of the time so make sure you have that at the audio circuit (trace speaker wires). There should be a larger regulator (normal size transister) for this. If v is low/high there then it will be less/more everywhere else.

I have not worked on your board. If you can turn the tv on but not off you will have a logic problem and it will be from a bad regulator most likely. If you can`t turn the tv on then you will have cap issues on the power supply.

I would look for another board if you can`t quickly find anything.

Tv boards are getting cheaper since tvs are also getting cheaper and soon not worth the repair.

The lcd tvs are junk now. I only repair the older plasma tvs with good picture and better audio (up to 2005).

That looks like an au-optronics panel (junk also).

I have replaced a lot of mainboards and I see problems all over with these newer units.

Good luck.

[budm]

Re: Vizio SV370XVT turns on won't turn off no video

OK, I looked at the picture of U12 (P/N? same as U33?), U33 (Dual P-CH MOSFET's).
U33 is used as switches for supplying the 12V for the T-CON board, when Gates are low, the U33 is turn on, it looks like the Gates are control by Q30 (the Voltage at the Base should toggle (which will also toggle Collector which I believe is connected to the Gates) voltage when the TV is turn on/off.
U12: I do not know what it is so I cannot tell by the pictures.
It seems to me that the processor is not sending the signals to turn on U12, U13.