Vizio SV422XVT - Standby light, no image, no sound.

[What?]

Re: Vizio SV422XVT - Standby light, no image, no sound.

I have checked ShopJimmy, ebay, the internet in general and no-one has this main board in stock or the only 2 sites I found it on wanted $180 american, go figure. So I am down to fix it myself or toss it, what a waste.

[dick_barton]

Re: Vizio SV422XVT - Standby light, no image, no sound.

Holy Cow, I just found one of the resistors while I was cleaning up my work station. Actual reading is 110 ohms, that must be R50, but I have no way of knowing, sorry.

Which two resistors did you lose. What numbers were they.
You have R50 as 110 ohms and R48 as 94.8 ohms in an earlier post.

[What?]

Re: Vizio SV422XVT - Standby light, no image, no sound.

dick-barton, I lost R48 and R50 in the process of modifying the resistor network for the U7 voltage regulator replacement so it would work. The original VR was adjustable and the replacement I had on hand was a fixed output VR so the resistors had to be removed in order for the replacement VR to work correctly. Since the modification worked I don't need the resistors. Thanks for your response, this forum is awesome!

[What?]

Re: Vizio SV422XVT - Standby light, no image, no sound.

The TV has been plugged in for about an hour, I touched every IC on the board with a bare finger. The chips range from cold to very warm, none were HOT.

[What?]

Re: Vizio SV422XVT - Standby light, no image, no sound.

Well, budm, according to your troubleshooting guide, I guess the next step is to look for bad diodes and transistors in the DC/DC section on the main board.

[What?]

Re: Vizio SV422XVT - Standby light, no image, no sound.

I am not having much luck finding bad diodes or transistors, but, I found this big smd and if I looked up the numbers correctly it is a schottky barrier rectifier. I tested this with a Simpson 260 analog meter set on 10k ohms and I got a full swing of the needle with the probes in either direction. Red to cathode and black to anode or red to anode and black to cathode got the same dead short reading. Doesn't that mean a bad diode, even for a schottky? There is 1.28 vdc at cathode to gnd and 0.004 vdc anode to gnd.

D155
S020F
SM540C

[dick_barton]

Re: Vizio SV422XVT - Standby light, no image, no sound.

Without lifting the diode to check or having the circuit diagram, it could be that the diode is across a low value resistor or an inductor.

[What?]

Re: Vizio SV422XVT - Standby light, no image, no sound.

BTW, for what ever it's worth, I am getting 2.18 vdc at all the switches and when I push the button the 2.18 goes through.

[What?]

Re: Vizio SV422XVT - Standby light, no image, no sound.

Ok, I will have to remove it and retest. I should have known that.
Thanks dick_barton.

[dick_barton]

Re: Vizio SV422XVT - Standby light, no image, no sound.

Here's some info on that set.

[budm]

Re: Vizio SV422XVT - Standby light, no image, no sound.

Looking at the pictures of the board from SJ: http://www.shopjimmy.com/vizio-3642-...r-sv422xvt.htm
That D155 looks to be for the Buck converter circuit consisting of D155, L3, C25, U2.
What resistance do you get using lower Ohm scale.

[What?]

Re: Vizio SV422XVT - Standby light, no image, no sound.

Thanks!! dick_barton

[What?]

Re: Vizio SV422XVT - Standby light, no image, no sound.

budm,
At Rx1K = 275 ohms and 250 ohms

a reading on my Fluke digital is 290 and 298 ohms

[What?]

Re: Vizio SV422XVT - Standby light, no image, no sound.

budm, you amaze me, all I see on this board is a bunch of components but you look at a picture and tell me what different sections are for. You must have a lot of time on these boards.

[budm]

Re: Vizio SV422XVT - Standby light, no image, no sound.

Can you read the P/N of U2?

[budm]

Re: Vizio SV422XVT - Standby light, no image, no sound.

BTW, check the resistance of D154 to see what you get, it is about the same setup as D155.

[What?]

Re: Vizio SV422XVT - Standby light, no image, no sound.

U2 is a DC/DC step-down regulator:
M021
G5684

http://pdf1.alldatasheet.com/datashe...GMT/G5684.html

[What?]

Re: Vizio SV422XVT - Standby light, no image, no sound.

D154 : Simpson @ Rx100: Red on cathode 400 ohms, red on anode 70 ohms.

Fluke set @ ohms: Red on cathode 468 ohms, red on anode 332 ohms

[What?]

Re: Vizio SV422XVT - Standby light, no image, no sound.

I was looking at the troubleshooting chart dick_barton sent to me, on the DC-DC converter trouble page at a check item that says "U5, U7 U88, U89 voltage is about 3.3v"
U5 is 3.3v, I just made U7 2.5v (oops), U88 and U89 are both 0V

Checking U50 because the chart said the voltage should be 1.2v with power on I got pins 1 thru 4 (source and gates) were 5v and pins 5 thru 8 (drains) were unstable dropping slowly from 5.12v to 0.745v jumping back up to 5.12v and dropping again over and over. U50 is a dual mosfet IC P06B03LVG

[What?]

Re: Vizio SV422XVT - Standby light, no image, no sound.

Budm,
I don't think anything was damaged by the overvoltage on U7, I traced where U7 goes and it looks like it only goes to the ethernet connector, unless there are layers in the middle of this board. Then that would mean U7 has nothing to do with powering up this main board.