# [SOLVED] VIZIO M550NV NO PICTURE NO SOUND



## salvamex

Please help.
I have a 55" vizio that when I connect it to the wall outlet, the vizio orange light flashes a lot of times and after a while it stays orange, I turn it on and the orange light turns to white but with no picture or sound. the whole screen is black.
I opened the tv and got the following readings once the tv was on (white vizio light) on the power supply board where I have placed the red circle on the picture.

from the bottom up
1.86v supposed to be 12v
1.86v supposed to be 12v
3.22v supposed to be 12v
3.32v supposed to be ?

Is this normal? I hope I am making sense and I am sorry for the poor pictures but its night time.


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## salvamex

*Re: VIZIO M550NV NO PICTURE NO SOUND*

I tested the two central 450v caps.
here are the readings:
the bottom one on standby 168v while it's on 396v
the top one on standby 168v while it's on 396v

What do you think?


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## octaneman

*Re: VIZIO M550NV NO PICTURE NO SOUND*

Hi salvamex


No, the readings are not normal they are too low the transformer isn't switching on. You will need to check the diodes and the bridge on the power supply first and the opto-isolators which I've circled. The opto-isolators separate the AC from the DC side of the pcb they also switch on the power transformer through a MOSFET or transistor , from there power is run to the regulator diodes that are on the heat sinks.

I've attached a file on how to test the opto-isolators because they are the most difficult to test. 

Question:

Have you checked ALL the fuses ? 

post back your findings.


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## salvamex

*Re: VIZIO M550NV NO PICTURE NO SOUND*

Thanks for the help, I am below newbie when it comes to electronics, so no I have not checked the fuses, which I dont know how or where they are. I am will to search to find out.
I maybe new but I am willing to learn and listen.


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## salvamex

*Re: VIZIO M550NV NO PICTURE NO SOUND*

I checked both diodes and on the cathode side I get a reading of .480 and when I switch the probes on the on the other end I get 0 reading.
and that is for both the diodes, so it means that are working because the current is flowing one way only right?


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## salvamex

*Re: VIZIO M550NV NO PICTURE NO SOUND*

what is the bottom one you circled? It does not have any markings so I am not sure if its a diode.


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## octaneman

*Re: VIZIO M550NV NO PICTURE NO SOUND*

The one on the bottom looks like a diode to me in the picture but I'm not sure because its not clear enough it may be a resistor. Yes, the diodes you tested are OK because current does flow in one direction only. On the heat sinks there is also voltage regulator diodes, if you look carefully at the symbols you see 2 diodes together that means that the diodes conduct both ways. But to test those you will have to desolder the pins to get accurate readings, take the numbers off the regulators and use a data sheet to find the correct pin-outs. We'll test the regulators one-by-one with power off and on but you will have to check the fuses first. (I've circled them) 

Testing the fuses is easy, set your meter on continuity if your meter is equipped with tone it will instantly tell you they are good or not. When the fuses are good you will get a beep sound if not you will not get a tone or readings off the meter it will indicate an open circuit. 

Have you tested the bridge and the opto-isolators yet ? Once you are done with those we'll test the main transformer and go deeper into troubleshooting the board.


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## salvamex

*Re: VIZIO M550NV NO PICTURE NO SOUND*

the one in the bottom it's all black with no marks on it (yellow circle), if it's a fuse it checks out fine. I tested all the fuses and they are okay. I tested all 6 diodes I can identify (red cricles) and they all check out okay but I have not tested the bridge and the opto-isolators because according to the text you attached, it says that I have to unsolder them in order to test them right? Also, how do you test the bridge?
If I have not said it yet, thanks man you are truly a kind and helpful person.


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## salvamex

*Re: VIZIO M550NV NO PICTURE NO SOUND*

oops, the one yellow circle on top it's suppose to be red circle, that one makes the 6th diode.


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## octaneman

*Re: VIZIO M550NV NO PICTURE NO SOUND*

Testing the bridge is no big deal all you need to do is set your meter on diode test and just follow these simple steps. 

On each pin of the bridge you will find these symbols. The first pair is the positive sign (+) the other the negative sign (-) . This is the DC output of the bridge. (40-50v D/C) 

The second pair are 2 sign waves (~) this is the AC input side of the bridge (110-120v A/C). 


The bridge tests like a regular diodes but since there are 4 of them in one package you test them like this:

1) Take the red probe of your meter and place it on the positive (+) sign and your negative lead to the first sign wave adjacent to the positive sign. Set your meter on diode test the diode should conduct one way. Reverse your leads for the second reading on the pins you shouldn't get a reading. 


2) Do the same thing to the negative as you did on the positive but only this time place your red lead on the negative sign and the black lead to the sign wave next to the negative sign. The meter should give a reading , reverse your leads and you shouldn't get a reading. 

The bridge is burned out in one of 2 ways. 

1) If you get readings on both sides of the diodes when you reverse your leads. ( bridge is shorted)

2) If you get no readings at all on either side even when leads are reversed. ( bridge is open) 


Remember to desolder the pins to get accurate readings. 

post back your findings.


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## salvamex

*Re: VIZIO M550NV NO PICTURE NO SOUND*

I need to buy me a solder gun and everything else I need for that 'cause I have never done that.


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## octaneman

*Re: VIZIO M550NV NO PICTURE NO SOUND*

All you need is a decent 40 or 50 watt soldering iron, solder sucker (or braid), solder flux, and a multi-meter for testing components.


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## salvamex

*Re: VIZIO M550NV NO PICTURE NO SOUND*

Thanks Octaneman for all the support.
You are great.
I decided to buy the power supply board, installed it and the tv works great.
I am sure I will be posting again soon to get more help on another tv.
Thank you again, I learned a lot.


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## octaneman

*Re: VIZIO M550NV NO PICTURE NO SOUND*

Good job ! :luxhello:


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## Kefali

You can learn more now by fault-finding the old PSU board.


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