Testing Power Supply on Vizio ST472XVT


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Testing Power Supply on Vizio ST472XVT

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techman995
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Mar 24, 2015, 10:46 PM

Post #1 of 12 (2322 views)
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Testing Power Supply on Vizio ST472XVT	Can't Post

I'm new to this forum and new to flat panel repair and hoping to find some answers here. I've got a Vizio ST472XVT that died a couple of weeks ago and I'm trying to fix it myself. It has no picture and no sound and will not turn on. I've been looking for help online and found a number of sources which say the power supply board may be the problem. I've got the set apart and have looked closely at all the boards including the power supply. The main fuse is good, I see no obvious burn marks, and no bulging capacitors. The next thing I was going to do was check the power supply voltages. To do this, the power supply must be turned on, which is a problem since the set will not turn on at this point. I've located the PSON terminal but am not sure what it needs to be connected to so the power supply will come on. The voltages are printed on the board, so I should be able to check them with my meter if I can get the board to power up. Any help on how to test this board is greatly appreciated. Thanks.

jts1957
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Mar 24, 2015, 10:56 PM

Post #2 of 12 (2319 views)
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Re: [techman995] Testing Power Supply on Vizio ST472XVT [In reply to]	Can't Post

'Your search - Vizio ST472XVT - did not match any documents.'
'Your search - ST472XVT - did not match any documents.'

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Location: Far, Far Away

(This post was edited by jts1957 on Mar 24, 2015, 10:58 PM)

techman995
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Mar 24, 2015, 11:03 PM

Post #3 of 12 (2314 views)
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Re: [jts1957] Testing Power Supply on Vizio ST472XVT [In reply to]	Can't Post

Sorry, I flipped the numbers. Maybe that's why I didn't get any results when I searched. Anyway, its really SV472XVT.

jts1957
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Mar 24, 2015, 11:42 PM

Post #4 of 12 (2310 views)
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Re: [techman995] Testing Power Supply on Vizio ST472XVT [In reply to]	Can't Post

+5VSB IS PRESENT?

Any power/other LED? Flashing or not?

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Location: Far, Far Away

(This post was edited by jts1957 on Mar 24, 2015, 11:43 PM)

techman995
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Mar 25, 2015, 1:15 AM

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Re: [jts1957] Testing Power Supply on Vizio ST472XVT [In reply to]	Can't Post

When everything went blank and quiet, the Vizio logo was still glowing steady white same as it did when the set was on and everything OK. I tried turning the unit off with the remote and the onboard switch at the side and the logo stayed on. Did the unplug, wait, and plug in routine and the logo came on orange but still no response to either remote or onboard on/off switch. Ever since then, Vizio logo is always glowing orange with no blinking and still no response to on/off. The logo has blinked in the past when downloading firmware updates. I haven't seen it blink at other times.

jts1957
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Mar 25, 2015, 1:31 AM

Post #6 of 12 (2302 views)
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Re: [techman995] Testing Power Supply on Vizio ST472XVT [In reply to]	Can't Post

Quote

The voltages are printed on the board, so I should be able to check them with my meter

Is the Stand By +5 Volts DC present (on the +5VSB pin) according to your meter?

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Location: Far, Far Away

techman995
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Mar 25, 2015, 5:46 AM

Post #7 of 12 (2295 views)
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Re: [jts1957] Testing Power Supply on Vizio ST472XVT [In reply to]	Can't Post

Yes! There is a bank of 4 of them on the opposite end of the connector from the PSON pin. They are all reading +5.16v. Thanks for the translation. Being new to this, I would not have guessed that SB means Stand By. Am I correct in thinking one of these needs to be connected to the PSON pin to turn the board on?

Thanks again!

jts1957
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Mar 25, 2015, 6:25 AM

Post #8 of 12 (2291 views)
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Re: [techman995] Testing Power Supply on Vizio ST472XVT [In reply to]	Can't Post

From a picture of the PS board, I'd say 5 pins, but whatever floats your boat.

+5VSB feeds Main Board. Keyboard & remote receiver connect to Main. When either power key is pressed, Main gives a voltage to PSON pin of PS (and it may or may not be 5 volts).

I'd check ALL supplies to their plug's ground reference (unless you can see that All grounds are same) for shorts before applying 5 volts to PSON.

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Location: Far, Far Away

(This post was edited by jts1957 on Mar 25, 2015, 6:36 AM)

techman995
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Mar 25, 2015, 9:09 PM

Post #9 of 12 (2272 views)
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Re: [jts1957] Testing Power Supply on Vizio ST472XVT [In reply to]	Can't Post

You're right, there are 5 pins. Didn't get close enough to see there are 5. Anyway, no shorts, applied 5 volts to PSON and everything came up the way it is supposed to. All voltages on pins were within .1 volt of what is labelled on the board. Any other thoughts?

Thanks.

jts1957
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Mar 25, 2015, 11:05 PM

Post #10 of 12 (2266 views)
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Re: [techman995] Testing Power Supply on Vizio ST472XVT [In reply to]	Can't Post

Be sure the stand-by voltage is reaching the Main board (and anywhere else wire(s) from the 5 pins go) and that all features and functions work. (Has sound - switches to other active sources, buttons all work, etc.)
Change Main board.

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Location: Far, Far Away

(This post was edited by jts1957 on Mar 25, 2015, 11:09 PM)

techman995
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Mar 26, 2015, 12:17 AM

Post #11 of 12 (2260 views)
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Re: [jts1957] Testing Power Supply on Vizio ST472XVT [In reply to]	Can't Post

Checked destinations of all standby voltages. They all went to the same connector on the main board. Measured voltage on solder posts of connector on bottom of board. All same readings of +5.15v, as on the PS board.

As I mentioned in the first message, there are no functions that work, no sound, no buttons, no picture, can't turn it on. One concern I have about replacing the main board is that I heard from another source the the LCD panel may have failed and this will prevent anything from turning on, even with a good main board. First of all, does this statement make any sense or is it just someone distributing misinformation on the internet? If this is a true statement, do you know of any way to verify if the panel is bad before I go to the trouble/expense of replacing the main board?

Thanks much for all your help.

jts1957
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Mar 26, 2015, 12:33 AM

Post #12 of 12 (2257 views)
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Re: [techman995] Testing Power Supply on Vizio ST472XVT [In reply to]	Can't Post

In Reply To

You're right, there are 5 pins. Didn't get close enough to see there are 5. Anyway, no shorts, applied 5 volts to PSON and everything came up the way it is supposed to. All voltages on pins were within .1 volt of what is labelled on the board. Any other thoughts?

Thanks.

Quote

Unless you mean something else by 'the way it is supposed to.'

If you meant the set works normally in all respects as long as YOU supply PSON voltage, then you would already know about panel.

I don't know the source or the statement.

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Location: Far, Far Away

(This post was edited by jts1957 on Mar 26, 2015, 12:35 AM)

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