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

[What?]

My problem started about 1 1/2 months ago, the tv failed to come on, had the orange standby light but when the power button on the remote was pressed the Vizio standby orange changed to white and blinked orange/white 24 times and then changed to steady orange. I checked fuses, looked for the obvious.... bad caps, burn marks, exploded components, bad solder joints and found nothing on the power board. Checked for voltage at connector CN201 which goes to the main board and found 5vdc only. No PS-ON, no 12V, no 18V, No BKLT-ON. I concluded the problem might be on the Main Board since 5V was reaching the Main. I tested all the fuses and found they were good, check all the caps for ESR and all were good, checked 4 voltage regulators and found U7 to be questionable,
U7
L362
G1117
Pin 1 (adj) = 1.259
Pin 2 (out) = 2.506
Pin 3 (in) = 5.128
I changed the regulator with a used one from a scrap PC board I had laying around. The replacement regulator is identified only as LD1117 and after installation I got the following readings,
U7
LD1117
Pin 1 (adj) = 2.24
Pin 2 (out) = 4.17
Pin 3 (in) = 5.09

The tv lit up and I got the V logo and the menu on the screen. Woo Hoo! I hooked up a coaxial antennae cable and got a beautiful HD picture and sound. Did the happy dance! I leaped to the conclusion the problem was solved especially since Vizio has a reputation for bad LDO Voltage Regulators, buttoned it up and put it back on the stand.
It has been 5 weeks working perfect, and then I tried to turn it on and got the original problem back. No image, no sound and blinking orange/white standby on the front of the tv. Heart break !
Drop back 10 yards and punt, I thought maybe the "used" LDO failed but it is getting almost exactly the same readings as immediately after install. So...now what? I retested 4 Voltage Regulators, 4 fuses, all the diodes and continuity between the power board connector and the main board connector, tested all the resistors associated with the regulators,
U5 U7 U71 U89
L362 LD1117 L362 L362
G1117 G1117 G1117
Pin 1 = 2.095 Pin 1 = 2.258 Pin 1 = 0.001 Pin 1 = 0.001
Pin 2 = 3.337 Pin 2 = 4.198 Pin 2 = 0.001 Pin 2 = 0.001
Pin 3 = 5.121 Pin 3 = 5.127 Pin 3 = 0.109 Pin 3 = 0.01

Fuses F4, F6, F10 and F13 all read 0.2 ohms.

I did not remove the diodes as they are all SMD but none of them read shorted.
I did not remove the resistors either for the same reason and they are really really tiny but none were open or shorted even though the readings were widely different between regulators.
Sorry for the long winded explanation but it seemed necessary.
Thanks so much for any assistance you may be willing to offer.
Help?

[budm]

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

U7
L362
G1117
Pin 1 (adj) = 1.259
Pin 2 (out) = 2.506
Pin 3 (in) = 5.128

U7
LD1117
Pin 1 (adj) = 2.24
Pin 2 (out) = 4.17
Pin 3 (in) = 5.09

The reading you have BEFORE changing the U7 is correct, the Vdiff between pin 1 and pin 2 should be 1.25V which is what you have, 2.506 -1.259 = 1.247V which is the internal Vref of the regulator. If the regulator is good, the Vout will be = to 1.25Vref + Vadj, so 1.25Vref +1.259Vadj = 2.509 Vout.

The replacement you installed has Vadj of 2.24V so the Vout should then be 1.25Vref + 2.24 Vadj = 3.49Vout. I can tell that it is not right because the difference between pin 1 and pin 2 should always be 1.25V. 4.17V is an odd Voltage for running the circuit, I doubt that the circuit designer comes up with that Voltage in mind.

So the board has been running with higher output Voltage. Are you sure the resistor network that are connected between the PIN 1 and GND, and pin 1 and PIN 2 are still in place? I doubt that the original U7 was bad.
U71, 89 do not have the input Voltage not until the main power supply is turned ON.
https://www.badcaps.net/forum/showth...999#post300999

[What?]

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

budm, thanks for your quick response,
For some reason I had in my mind that the output should be 3.3v rather than 2.5v.
I will remove the LD1117 and check the resistors and get back to you.
Can you recommend a replacement LDO regulator? I don't think the original is available and I destroyed the original removing it from the board.

[budm]

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

1117 series Fixed or Adjustable is just a generic LDO which you can get them from DIGIKEY or MOUSER.

[What?]

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

OK, it appears the resistor network is intact as well as the 2 capacitors....
using a Fluke 115 meter set on ohms and an ESR meter I got the following reading,
Pin 2 to R48 =.01 ohms
Pin 1 to R48 = .01 ohms
Pin 1 to R50 = .01 ohms
R50 to GND = .01 ohms
R50 to R48 = .01 ohms

R48 = 94.8 ohms
R50 = 110 ohms

C38 ESR = .19 ohms and is connected pin 3 to GND
C39 ESR = .09 ohms and is connected pin 2 to GND

Pin 1 to GND = 110 ohms
Pin 2 to GND = 204.7 ohms

If the original VR was good and the tv did not work why did the tv start working when I put a bad VR in?
I added a close up photo of U7 for reference

[budm]

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

So what was the Voltage reading of U7 (LD1117) when the TV failed the second time? 4.17V at the output?
May be something got disturbed in that area and it starts working, I just hope that nothing got damaged running at 4.17V instead of 2.5V.

[budm]

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

Based on the value of R48 (FBr, 94 Ohms) and R50 (ADJr, 110 Ohms) measured in the circuit, the Vout should be around 2.7V.

[What?]

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

Yes, Pin 2 (out) had voltage reading of 4.198
I am hoping nothing got damaged too, the board is no longer available so it would be very difficult to get a replacement. I am thinking something got damaged, what else would cause it to quit.
I had 3 identical salvaged boards with the LD1117 VR and I think the markings got messed up when I removed the one I used. I just dug out one of the other boards to verify the number and the ID is actually LD1117 25A. So that means it is a fixed 2.5V regulator, so if I change/remove the resistors to comply with installation of a fixed regulator it would put out the 2.5 volts instead of 4.17, right?

[budm]

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

Yes you should get 2.5V for that 1117-25 fixed regulator.

[What?]

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

Alright then, I will give a try!

[What?]

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

budm,
How did you calculate the LD1117 Vout should be 2.7v?

[What?]

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

Alrighty then, that worked, now I have Vo=2.5v @ U7. Actual measurements are:

U7
LD1117
25A
Pin 1 (gnd) = .004
Pin 2 (out) = 2.505
Pin 3 (in) = 5.115

I have included a photo of U7, I removed SMD R48 and R50, I soldered a jumper from Pin 1 to GND.

That solved the overvoltage at U7 Pin 2 but now I still have the original problem. The Vizio ON/STBY light blinks orange/white pauses on orange and blinks again. No screen image, no backlight, no sound.

[budm]

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

The spec sheet of the 1117 has the formula for calculating the Vo.
I also made the spread sheet for it too, see post #6
https://www.badcaps.net/forum/showth...999#post300999
To get the accurate result you will need to check the resistors values off the board.
So can you check the actual value of those two resistors?

[budm]

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

BTW, so what dcv do have for the PS-ON, BL-ON pins on the power supply?

[What?]

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

Still have the original readings at the power supply connector CN201 which goes to Main Board connector J1 and that is 5vdc only, no other readings.

The 2 smd resistors are very tiny and either due to my lack of experience or the equipment I have, both resistors were lost immediately after removal. I think they in a ball of solder in my carpet.

[budm]

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

Try heating the main board with hair dryer, disconnect other boards (such as WIFI, IR board) that are connected to the main board except the power supply board and see what happen.
http://www.shopjimmy.com/catalogsear...Vizio+SV422XVT

[What?]

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.

[What?]

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

Ok, I will try the hair dryer. For what it's worth, I noticed the heat sink on one of the big processors is warm but the other one is cold.

[budm]

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

BTW, you may want to search badcaps site for the 'Vizio SV422XVT' to see other threads that may have the same problem as yours.

[What?]

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

Thanks budm, I did a search before I posted and spent a few hours reading posts for the same model, that is what led me to the U7 voltage regulator.

Heating the board mostly around area near the J1 connector did not make any changes. I don't have a can of air or freeze spray to try, I will have to run to Radio Shack to see if they carry it.