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Old 06-27-2011, 11:36 AM   #1
tlm387
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Default Vizio SV470XVT1A LCD No Picture/No Backlight

I snagged a 47in Vizio LCD that is not working from Craigslist. I have very little background information about why/when it failed and what it did.

When I got it home and plugged it in the power supply clicked once and the amber VIZIO light lit up and then turned WHITE without me pressing ANY buttons. Upon it turning white (powering itself on?) it did not make any other clicks from the PSU.

I could hear the very faint/normal speaker pop. There is no backlight, no picture, and the side panel buttons are completely unresponsive. I have to unplug it to turn it off.

The power supply unit in this TV is nicely labeled. The power cable going to the main board has 3 12volt pins and 3 5volt standby pins as well as one labeled PSON. With the TV plugged in and turned on (the only way I can test it because I can't get it into standby mode)

The 5volt pins each have 5.14 volts.
The 12volt pins each have 11.76 volts (less than 12)
When I test the PSON it shorts out the TV and the relay on the PSU clicks on and off.

There are 2 24volt pins going to the sound board both read exactly 24.1v

There are 2 inverter boards and each one has 5 24volt pins coming off the PSU

All the 24volt pins have 23.8 volts.

The inverters and the main board are getting just under their correct voltages.

Are these low voltages far enough off to cause problems?
Why does the set power on by itself after plugging it in?
Is the power supply the most likely culprit here?

I do not have the remote and I do not see any bad capacitors.
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Old 06-27-2011, 03:00 PM   #2
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Default Re: Vizio SV470XVT1A LCD No Picture/No Backlight

Please post pictures of the overall layout of boards and each one individually. Use "Manage Attatchments" whenever posting pictures.

Check inverter fuses as well.
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Old 06-27-2011, 03:08 PM   #3
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Default Re: Vizio SV470XVT1A LCD No Picture/No Backlight

Also check U33 on the main board. (Common problem on some series of Vizio that results in these symptoms).

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Old 06-27-2011, 04:21 PM   #4
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Default Re: Vizio SV470XVT1A LCD No Picture/No Backlight

The voltage going into the main board is less than 12 volts. Could the low voltage cause these problems?

On my main board U33 looks like an IC with 8 pins. Which pins should I test and what should the voltage be?

Last edited by tlm387; 06-27-2011 at 05:18 PM..
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Old 06-27-2011, 05:56 PM   #5
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Default Re: Vizio SV470XVT1A LCD No Picture/No Backlight

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Originally Posted by tlm387 View Post
The voltage going into the main board is less than 12 volts. Could the low voltage cause these problems?

On my main board U33 looks like an IC with 8 pins. Which pins should I test and what should the voltage be?
How much less? 11.8 wouldn't be unusual. 10.5 would make me wonder, anything below 10.0 would raise red flags.

Different version of the main board; disregard my earlier suggestion.

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Old 06-27-2011, 06:04 PM   #6
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Default Re: Vizio SV470XVT1A LCD No Picture/No Backlight

Reminder, pics please. Help us help you.
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Old 06-27-2011, 07:44 PM   #7
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Default Re: Vizio SV470XVT1A LCD No Picture/No Backlight

Pictures are on the way, just as soon as the camera battery charges.

The voltage coming out of the power supply and into the main board is 11.75v. The power button works sometimes, but not consistently at all. And if it does work it only works one time.

The TV came with a replacement main board that was purchased online, I dont have any way of knowing if the replacement board is in working order but the TV exhibits the exact same symptoms with either board installed. I suppose there is a chance that both boards have failed in the same way, but that seems unlikely.
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Old 06-27-2011, 08:21 PM   #8
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Default Re: Vizio SV470XVT1A LCD No Picture/No Backlight

Well, that is a good assumption but it's only half. Like you said:

"I suppose there is a chance that both boards have failed in the same way"

OR

Both boards could be fine and another board is failing you.
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Old 06-28-2011, 12:02 AM   #9
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Default Re: Vizio SV470XVT1A LCD No Picture/No Backlight

Here are the pictures
I really appreciate any and all advice. Can anybody figure out why the TV would automatically go from standby to on by itself after being plugged in. That really does not make sense to me.

Also why would the power button only work sometimes and only once or twice at a time?

I do not have a service manual for this TV but I am fairly certain that the main logic processor is on the main board. If it is being under powered that might explain the unresponsive buttons.
Attached Images
File Type: jpg DSC01288.JPG (143.0 KB, 130 views)
File Type: jpg DSC01289.JPG (133.2 KB, 107 views)
File Type: jpg DSC01290.JPG (141.2 KB, 97 views)
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Old 06-28-2011, 08:23 AM   #10
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Default Re: Vizio SV470XVT1A LCD No Picture/No Backlight

One of the first steps would be to check the output of the LDO regulators on the board. I've identified 6 and circled them.

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Old 06-28-2011, 10:27 AM   #11
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Default Re: Vizio SV470XVT1A LCD No Picture/No Backlight

My apologies for being a novice, but some of these voltage regulators have 3 pins connected and others only have 2 pins connected.

The ones that have 3 are labeled In Ground Out
The ones that have 2 are labeled Ground VO VI with the center pin VO disconnected.

In the picture you can see the center pin of one LDO is not connected. How do I test the ones with only 2 pins?
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Old 06-28-2011, 11:05 AM   #12
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Default Re: Vizio SV470XVT1A LCD No Picture/No Backlight

Quote:
Originally Posted by tlm387 View Post
My apologies for being a novice, but some of these voltage regulators have 3 pins connected and others only have 2 pins connected.

The ones that have 3 are labeled In Ground Out
The ones that have 2 are labeled Ground VO VI with the center pin VO disconnected.

In the picture you can see the center pin of one LDO is not connected. How do I test the ones with only 2 pins?
The tab is the third pin.

One well known secret is if you Google the part number, followed by datasheet you often will find the datasheet for the device. The datasheet has a wealth of information, including the pinout.

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Old 06-29-2011, 12:17 PM   #13
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Default Re: Vizio SV470XVT1A LCD No Picture/No Backlight

The identification numbers of the 6 voltage regulators are as follows:
There are 3: (circled in red)
1804
0809BL
The voltages are:
Vi to ground
1. 2.73v
2. 3.91v
3. 2.75v

Vo/Tab to ground
1. 1.250
2. 1.251
3. 1.248
(I can not find a datasheet for these)

There are 2: (circled in blue)
AZ7805T - E1
820J71
The datasheet specifies that these are 5.0 V output
They both measure from Vin to Vout 11.75v to 5.1v

There is 1: (circled in yellow)
K363
G1117
It has no VO/VI/GNd labels however i found that the tab is the ground
PIN 1 to Ground/Tab 1.24v
PIN 2. to Ground/Tab 1.25v

This one seems the most suspicious to me, however I suppose there is a chance I am not reading it correctly.

With regards to the backlight, if it is getting voltage from the power supply why is it not turning on?
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Old 06-29-2011, 12:38 PM   #14
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Default Re: Vizio SV470XVT1A LCD No Picture/No Backlight

Quote:
Originally Posted by tlm387 View Post
The identification numbers of the 6 voltage regulators are as follows:
There are 3: (circled in red)
1804
0809BL
The voltages are:
Vi to ground
1. 2.73v
2. 3.91v
3. 2.75v

Vo/Tab to ground
1. 1.250
2. 1.251
3. 1.248
(I can not find a datasheet for these)

There are 2: (circled in blue)
AZ7805T - E1
820J71
The datasheet specifies that these are 5.0 V output
They both measure from Vin to Vout 11.75v to 5.1v

There is 1: (circled in yellow)
K363
G1117
It has no VO/VI/GNd labels however i found that the tab is the ground
PIN 1 to Ground/Tab 1.24v
PIN 2. to Ground/Tab 1.25v

This one seems the most suspicious to me, however I suppose there is a chance I am not reading it correctly.

With regards to the backlight, if it is getting voltage from the power supply why is it not turning on?
The numbers are interesting. The first three output voltages are a common voltage used by processors, although the varying input voltage puzzles me.

The two circled in blue certainly seem normal.

The 1117 family of LDO regulators are quite common, although usually the output voltage is incorporated in the part number. The fact that input and output voltages are the same seems to indicate a real problem.

What is even more surprising is there is no 3.3 volt output on any regulator.

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Old 06-30-2011, 11:27 PM   #15
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Default Re: Vizio SV470XVT1A LCD No Picture/No Backlight

I'm going to put in the replacement (unknown condition) main board that the seller provided with the TV on Friday. I will duplicate the tests to see if I get different results.

I am still puzzled why there is no backlight if it has the correct voltage (24v) being fed into it. What other circuits are used to operate the backlight? Is there a way to test the other circuits causing the backlight failure.
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Old 07-01-2011, 12:19 AM   #16
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Default Re: Vizio SV470XVT1A LCD No Picture/No Backlight

Quote:
Originally Posted by tlm387 View Post
I'm going to put in the replacement (unknown condition) main board that the seller provided with the TV on Friday. I will duplicate the tests to see if I get different results.

I am still puzzled why there is no backlight if it has the correct voltage (24v) being fed into it. What other circuits are used to operate the backlight? Is there a way to test the other circuits causing the backlight failure.
The inverter is controlled by the main board. There are two signals, one turns it on / off, the other adjusts the brightness.If you examine the power connector to the inverter it becomes obvious. Of course, that provides a troubleshooting clue in some cases.

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Old 08-30-2011, 08:53 PM   #17
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Default Re: Vizio SV470XVT1A LCD No Picture/No Backlight

Quote:
Originally Posted by tlm387 View Post
I'm going to put in the replacement (unknown condition) main board that the seller provided with the TV on Friday. I will duplicate the tests to see if I get different results.

I am still puzzled why there is no backlight if it has the correct voltage (24v) being fed into it. What other circuits are used to operate the backlight? Is there a way to test the other circuits causing the backlight failure.
I'm assuming you got it fixed?
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Old 10-27-2011, 10:47 PM   #18
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Default Re: Vizio SV470XVT1A LCD No Picture/No Backlight

IF you need the service manual, for the Vizio sv470xvt1a, I have it.
PM me with an email address and I'll send it to you.

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Old 11-06-2011, 07:37 PM   #19
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Default Re: Vizio SV470XVT1A LCD No Picture/No Backlight

I have the same tv with the same problems and know the problem is in the power supply. Does your service manual have board schematics in it, and if so, could I get a copy of the manual from you? Thank you.
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Old 11-08-2011, 11:27 AM   #20
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Default Re: Vizio SV470XVT1A LCD No Picture/No Backlight

I would say it is either one,or both of the inverters under the small metal covers on the left,and right of the TV.I had a coulple of TVs with the same style inverters.Usually one,or more of the capacitors,IC,or transistors goes bad on either,or both of the inverters.I hope this helps.Please let me know.Thank You very much!

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