Vizio sv421xvt No Video, Audio or Backlight

[bottleneck]

I have a 42" Vizio that stopped working, it appears to be common from what i have been reading. I have read alot of threads on here concerning these boards. There is a wealth of information and knowledge. I havent found out what my issue is as i am limited when it comes to component level troubleshooting. I have a desire to learn and appreciate the wisdom from the members hear! I have included photo's and the troubleshooting diagram from the service manual I followed. The Vizio emblem is yellow in standby and white when powered on. I am hoping someone here can help me get this tv working again. Here is what i have discovered so far.

1. went through list on troubleshooting sheet
2. 5v standby appears to be good
3. No 12v (seems to be controlled by the mainboard from reading other threads)
4. Every other voltage measurement meets the troubleshooting guide until U6 Nothing there
5. U10 looks to be correct as well (if i am counting the pins correctly)
6. Didnt find any bad fuses that i could see (continuity test)
7. The fuse to the left of PS_ON has no power but checks to be good
8. PS_ON with the unit powered on is 2.25v
9. INV_ON/OFF with the unit powered on is 3.25

I have tried to disconnect the Tboard and inverter cables then powered it up to see if the power supply or Mainboard would give me any other readings and it doesnt. There is no voltage going to the Tboard that i can see.

Hoping someone will have some wisdom to pass on.

[budm]

Re: Vizio sv421xvt No Video, Audio or Backlight

So far the main board is sending the correct signals (PS_ON, BL_ON).
This is power supply-inverter board combination. The inverter circuits run off the 390~400v PFC power supply section (need to see the voltage rating on that large DC filter cap under the heat sink)
The problem can be the inverter circuits, inverter transformers, bad caps, bad lamps, bad ballast caps (small blue caps by the lamp connectors).
Can we get good close up of the power supply from both sides of the board in 1/4 section so we can really blow up the pictures to see the details of the board.

[retiredcaps]

Re: Vizio sv421xvt No Video, Audio or Backlight

I have a desire to learn and appreciate the wisdom from the members hear!

Since you are willing to listen, I'll make some suggestions.

1. went through list on troubleshooting sheet
2. 5v standby appears to be good
3. No 12v (seems to be controlled by the mainboard from reading other threads)
4. Every other voltage measurement meets the troubleshooting guide until U6 Nothing there
5. U10 looks to be correct as well (if i am counting the pins correctly)
6. Didnt find any bad fuses that i could see (continuity test)
7. The fuse to the left of PS_ON has no power but checks to be good
8. PS_ON with the unit powered on is 2.25v
9. INV_ON/OFF with the unit powered on is 3.25

The words above in your list, namely, "good", "looks to be", etc are subjective.

We prefer to see the actual measurements and can confirm your interpretation. About once every 2 weeks, we get some new who writes they test "good" only to find out they misinterpreted the results. I'm not suggesting you have made any mistakes, but for future posts, we prefer to see the actual readings.

Using continuity to test a fuse can yield false results (see above). Some multimeters will beep "continuous" for any resistance reading under 1800 ohms. A good fuse should measure less than 1.0 ohms.

Continuity is an useful feature to have and use, but not for testing fuses.

[bottleneck]

Re: Vizio sv421xvt No Video, Audio or Backlight

Thank you both for jumping in here! I have included more pictures of the power supply let me know if you need more(it doesnt look like i can get the heatsink out of the way short of removing everything).

I appologize for my lack of detail. The last thing i want to do is waste time going down the wrong road. I know your time is valuable! I have included the information i left out of my first post. Let me know if i missed something.

J1 - stndby
p10 - 5.19v
p11 - 5.19v
p12 - 5.19v

(12v) - pins
p2 - 0
p3 - 0
p4 - 0

U1
p5 - 5.08
p6 - 5.08
p7 - 5.08
p8 - 5.08


U2(p2) - 3.28
U3(p2) - 3.30
U5(p2) - 3.31

U9(p2) - 1.82

U7(p2) - 3.30

U4(p2) - 1.25

U6(p2) - 0

U10(p7) -1.1

fuses test at 2.8 ohm

Let me know if you need anything else.

[bottleneck]

Re: Vizio sv421xvt No Video, Audio or Backlight

I realized i didnt add the bottom. Sorry about the flash, if it poses a problem i can retake it later when there is daylight. I guess i was focused at the componant with no reading. of course you have been doing this for awhile.

[tom66]

Re: Vizio sv421xvt No Video, Audio or Backlight

For the regulators, you need to also specify the input and adjust pin voltages. The input voltage is necessary so we can see if the regulator is getting power (and whether it should work), the adjust voltage helps determine if the output voltage is correct. Also the part number, if you can read it, would help a lot.

[bottleneck]

Re: Vizio sv421xvt No Video, Audio or Backlight

I did some more checking. I have included voltage measurements and some numbers off of the chips. Let me know if i need to clarify anything? I also tried to take a measurement off the main cap on the power supply. I wasnt sure which side this was on. It looks to me like the AC side I am reaching the limits of my componant ability at this point. Please clarify if i am incorrect. I was careful as i know that we are dealing with high voltage. I was sure that I was only touching the legs of the capacitor.

With my meter on the + and - of the cap which is 120uf 450v i got 283v with my meter on AC. It bounced back and forth from OL to 283v. Since i wasnt sure i checked it with DC and got 165v.

Let me know if i missed something else, or if i need to clarify something.

Thanks for the help!

[bottleneck]

Vizio sv421xvt No Video, Audio or Backlight

I did some checking on the power supply. I noticed a couple of ceramic caps didnt have any resistance. From what i have read this could be because i only was using a DM. could someone verify if this is true?
I checked for voltage accross the legs Powered on/off and only got 120voltage on one of them (see photos) could this be the problem? if so what would the replacement caps be? I am hoping for some more instruction from the experienced ones.

Thanks!

[bottleneck]

Re: Vizio sv421xvt No Video, Audio or Backlight

I realize i should have done a little more reading before posting. I am sure this helps reduce confusion of inacurate posts by the information being in the proper format. I could use some help as to where and what to look for next.

I followed the instruction by retiredcaps concerning regulators(I should have read this first)!

See the information below:

U2
L271
G9117
pin 1 = 2.03
pin 2 = 3.28
pin 3 = 5.17

U3
1084
0932dl
pin 1 = 2.05
pin 2 = 3.30
pin 3 = 5.05

U4
L271
G9117
pin 1 = 0
pin 2 = 1.25
pin 3 = 3.29

U5
1084
0932dl
pin 1 = 2.06
pin 2 = 3.30
pin 3 = 5.05

U6
L271
G9117
pin 1 = 0
pin 2 = 0
pin 3 = 0

U7
L271
G9117
pin 1 = 2.05
pin 2 = 3.30
pin 3 = 5.05

U8
mc
7805ct
RAA931G
1 = 0
2 = 0
3 = 0

U9
1084
0932dl
pin 1 = .56
pin 2 = 1.81
pin 3 = 3.30

Does U4 Look bad?

One other question i have is originally i posted that the PS_ON voltage was 2.25v with it powered on. I have read other threads on here they state it should be above 3v is this accurate? I can follow instructions, however i am at a loss at this point where to proceed next.

Any help would be appreciated!

[retiredcaps]

Re: Vizio sv421xvt No Video, Audio or Backlight

I followed the instruction by retiredcaps concerning regulators(I should have read this first)!

Format matters as tom66 asked for in post#6. We do not have physical access to your boards. Some people have no understanding how difficult remote troubleshooting is.

In one recent thread, the OP got all pissed off at a regular because he reported his readings all in one line making it impossible to read and decipher even though a clear example of what we needed was provided. When I see that disrespectful treatment directed at a regular, I hit close window and never return to help the OP.

It is 12:44AM in the morning as I write this and when I click on new posts, there are 66 new threads. If the information is easy for us to digest (paragraphs, periods, punctuation, clear pictures, ability to follow instructions), we are more likely to respond. Otherwise, I hit close window and move on.

U4
L271
G9117
pin 1 = 0
pin 2 = 1.25
pin 3 = 3.29

Does U4 Look bad?

The readings say it is good. My "how to test" guide tells you why.

One other question i have is originally i posted that the PS_ON voltage was 2.25v with it powered on. I have read other threads on here they state it should be above 3v is this accurate?

There is no universal standard AFAIK. Most of the time, I see > 3V required. You can try to trace the 2.25V to see where it is originated. That might lead you to a damaged component?

[retiredcaps]

Re: Vizio sv421xvt No Video, Audio or Backlight

I noticed a couple of ceramic caps didnt have any resistance. From what i have read this could be because i only was using a DM. could someone verify if this is true?

Your multimeter is probably not sending enough current through those caps so they should read open circuit.

[retiredcaps]

Re: Vizio sv421xvt No Video, Audio or Backlight

One other question i have is originally i posted that the PS_ON voltage was 2.25v with it powered on. I have read other threads on here they state it should be above 3v is this accurate? I can follow instructions, however i am at a loss at this point where to proceed next.

It didn't dawn upon me early, but a simple test would be to disconnect all your boards. Use 2 AA batteries in series or a single 3V CR2032 battery and apply 3V to the PS_ON pin. If the power board starts, then you know 3V is required.

To verify, get 2 weak AA cells so they are approximately 2.25V in series and retest.

1:30AM. Off to bed.

[bottleneck]

Re: Vizio sv421xvt No Video, Audio or Backlight

[QUOTE=retiredcaps;292232]It didn't dawn upon me early, but a simple test would be to disconnect all your boards. Use 2 AA batteries in series or a single 3V CR2032 battery and apply 3V to the PS_ON pin. If the power board starts, then you know 3V is required.

To verify, get 2 weak AA cells so they are approximately 2.25V in series and retest.
QUOTE]

Great Idea! I tried this with both new AA and used AA batt(from a remote). No change. I did notice that when i turned it on the 12v side goes up to about .05v. When i power it off it goes back to 0. This is the same when i have the main board plugged in. So it appears with the powerboard isolated there is no change.

I also checked my main cap (120uf 450v) on the powerboard.
stdby = 172v DC
on = 166.5v DC
Does this mean something could be drawing it down? I am unsure of where to go from here, any ideas?

[budm]

Re: Vizio sv421xvt No Video, Audio or Backlight

The voltage on that main cap should go up to around 390VDC if the PFC kicks on when PS_ON is applied. Did you find out how much the replacement power supply-inverter board combo is?

[bottleneck]

Re: Vizio sv421xvt No Video, Audio or Backlight

The voltage on that main cap should go up to around 390VDC if the PFC kicks on when PS_ON is applied.

This is what i had read in some of your other posts. Is there anything that stands out i could test, or should i replace the cap and see?

Did you find out how much the replacement power supply-inverter board combo is?

I have been looking for one and believe i can get one for around $70 - $80. I would hate to order one and have it not the issue.

I respect your opinion.

[budm]

Re: Vizio sv421xvt No Video, Audio or Backlight

To troubleshoot this combo board is not going to be easy, so far we already know that from your ealier post showing the PS_ON an d the INV_ON signals are OK. Next thing is to look up all the spec sheets of the PFC Controller IC, SMPS IC so you can check the voltages on the IC's pins. Next step is to trace out the copper traces to see how the circuits are connected together, that is what I have to do when I do not have the diagrams for the boards.

[bottleneck]

Re: Vizio sv421xvt No Video, Audio or Backlight

I wanted to report back that my television is fixed!

Due the the generous efforts and dedication to the following...Budm, RetiredCaps, and Tom66.

I have learned alot from you all and hope that some day i can return what you have dedicated for others...

I ended up ordering a Power supply. The model PLHL-T848A is a replacement or compatible model for this television. It is working great! I did find out through this that i really enjoy the challenge and look forward to saving other devices from the fate of the landfill...

Thanks Again!

[budm]

Re: Vizio sv421xvt No Video, Audio or Backlight

Great job and thanks for the repair feedback.