# Vizio M550NV has sound but no video please help



## greekoneson (Jul 24, 2012)

The tv flash orange and white when its plugged in after its been unplugged and its does it for 15-20 secs then can be turned on. Once on it has no video or picture at all the backlight works but all i see is grey. I dont know which board needs replaced or what else to check. If anyone has any ideas please help out.


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## octaneman (May 13, 2009)

Hi greekoneson


Does the audio still work ?


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## greekoneson (Jul 24, 2012)

Yea audio still works.


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## octaneman (May 13, 2009)

The problem is with the inverter board.


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## greekoneson (Jul 24, 2012)

Which one is that? I can take a pic if you could show me.


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## octaneman (May 13, 2009)

greekoneson said:


> Which one is that? I can take a pic if you could show me.


Sure, no problem .


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## greekoneson (Jul 24, 2012)

ImageShack® - Online Photo and Video Hosting

Let me know if its good enough


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## octaneman (May 13, 2009)

I see the main board but you need to get closer pics of the next 2 boards


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## greekoneson (Jul 24, 2012)

ImageShack Album - 3 images

Hows that


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## octaneman (May 13, 2009)

Good enough. 

This particular model has a consistent problem with the back lights which is through the power supply board. But in order to be absolutely sure that it is the power supply and not the video side of the board, you need to take voltage readings with a DMM. 


Question: 

At the rear of the panel you will see small holes for the back light, when you power it up do the lights turn on ? If not the problem may not lie with your board but the lights.


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## greekoneson (Jul 24, 2012)

Yea they light up heres a pic
ImageShack® - Online Photo and Video Hosting


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## greekoneson (Jul 24, 2012)

I got a voltage meter but dont know what to set it on and what to check


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## octaneman (May 13, 2009)

Did your set turn on/off/on/off and then it shut down ?


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## octaneman (May 13, 2009)

greekoneson said:


> I got a voltage meter but dont know what to set it on and what to check



Ill show you what to check but please be very careful where you place your meter leads to avoid injury or damage to the set ok ?


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## greekoneson (Jul 24, 2012)

If i leave it on after 10 minutes it turns off by itself ....but when i unplug it and plug it back in i press power and the only thing that comes on is the vizio logo it flashes on and off for 20 secs then once it stops i press the power button again and it comes on.


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## greekoneson (Jul 24, 2012)

Ok il check whatever you need me to.


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## octaneman (May 13, 2009)

There are 2 possibilities; 1) Inconsistent voltage feed from the power supply 2) The set is overheating causing a thermal shutdown. 


The first thing you should do is do is a visual inspection of all the capacitors on all the boards. If any are bloated or misshapen in any way they have to be replaced. The board has 3, 5, 12, 24 volts running through it all these voltages have to be checked. 

The second thing you need to do is disconnect the white molex connector off the power supply and check all the voltages to the pins. On the board itself is printed the voltages that need to be on those pins for the monitor to work, take a close up picture of the pins and ill show you which pins to probe with your meter.


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## greekoneson (Jul 24, 2012)

No caps are blown as far as i know(triple checked) Here a pic and i hope i took the right one.


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## octaneman (May 13, 2009)

greekoneson said:


> No caps are blown as far as i know(triple checked) Here a pic and i hope i took the right one.




Yes it is, 
Set your meter on 20V D/C.

Now you see there are 3 molex connectors you will disconnect them and you will check the voltages at the pins. The 5 volt pins have to stay on 5 volts at all times, if the voltage is not there check the 18 volt pins. The multi-pin connector has BL_on and PWR_on. BL stands for back light which is on the third pin , and the fourth pin PWR_on stands for power on. The voltages on the BL_on and PWR_on pins have to be solid and should not be fluctuating. Going from left to right from the PWM pin the 5th, 6th, 7th pins are 12 volts. The 8th, 9th, 10th, 11th pins are ground , the 12th, 13th, 14th pins are 5 volts.


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## greekoneson (Jul 24, 2012)

Ok i got the meter on 200 ac im guessing thats right cause im gettin 124 from the power plug. I checked the 5v and im getting 10 from them and the 18v and pwr on im getting nothing. Am i doing this right?


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## octaneman (May 13, 2009)

greekoneson said:


> Ok i got the meter on 200 ac im guessing thats right cause im gettin 124 from the power plug. I checked the 5v and im getting 10 from them and the 18v and pwr on im getting nothing. Am i doing this right?


The voltage outputs from the pins are D/C not A/C. 
Is your meter set to 20v D/C scale when you took the readings off the pins ? 


18 volts is the main voltage to the board since its not there, either a power mosfet to the switching transformer is fried or there is a problem with the transformer itself. You will need to double check your readings, make sure your meter's negative leed is on a good ground when doing your test.


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## greekoneson (Jul 24, 2012)

Ok im getting juice only from the 5v which is 4.90 all the others get nothing.


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## greekoneson (Jul 24, 2012)

Ok i plugged the connectors back in and turned the tv on then check....there all getting the correct voltage. 18v 12 and 5v. PWR and BCK LIGHT are getting around 3v. So im geussing there good?


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## greekoneson (Jul 24, 2012)

If its not the power board what do you think it could be?


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## octaneman (May 13, 2009)

greekoneson said:


> If its not the power board what do you think it could be?



Its looking more an more like the main video board, but to be sure you have to verify the 3.3v going to the board on the molex connector.


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## greekoneson (Jul 24, 2012)

By 3.3v you mean through the pwr on and bck light wires? All the volts are traveling from one board to the other without a problem.


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## octaneman (May 13, 2009)

If the 3.3 volts is on the main board then the problem lies with the video signal from the main board. If the voltage is *not* there the problem is with either the power boards's voltage regulator or the main board's regulator.


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## greekoneson (Jul 24, 2012)

Yup the 3.3 volts from the power board is going through to the main board. I check the legs on both and there both pwr on and bck light getting power.


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## octaneman (May 13, 2009)

So far everything points to the video picture signal but you would need an oscilloscope to verify it. The back lights are on and all voltages are present its the processor thats not switching on i'd replace the main board.


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## greekoneson (Jul 24, 2012)

Gotcha i just ordered one and once it gets here i will let you know on the outcome. I appreciate the help man.


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## octaneman (May 13, 2009)

Anytime. :thumb:


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## greekoneson (Jul 24, 2012)

Well i got the board but i hope its just the wrong version of it. There an (a) at the end of the one i just got and mine has a (b) so there different versions. The remote does not work with the one i ordered and shows no video...but it does dimm the screen a few seconds after i turn it on. I contacted the person to send the correct version and i hope it will work.


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## octaneman (May 13, 2009)

Keep us posted of your progress.


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## greekoneson (Jul 24, 2012)

Just got the board and its doing the same thing....the remote does not work with the replacement board ...shuts the tv off after a few minutes and does not display a thing. Maybe the lcd is burnt or the tcon board is bad or maybe even a ribbon cable?....which would you think cause i am totally lost on this one.


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## octaneman (May 13, 2009)

On your original post the back lights were coming on but on the new board they are not. 

Are you sure you got the correct board for your set? Do the serial numbers match ?

Do you see the back lights come on and stay on or does it shut off ?


No, its not the LCD thats burned double check your CCFL tubes if you see any bulbs that have a dark patch on the ends of it its burned. The problem with CCFL's is that if one is bad all of them shut off because they're connected in series. Look your ribbon connections make sure its straight in to its connector and its on tight.


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## greekoneson (Jul 24, 2012)

Serial numbers dont match but the model numbers do exactly. The back light comes on with the new board. The difference with the new board when its on is that the remote does not work, it shuts off after just a few mintues of being on. The old board when connected stays on , remote works and it does not shut off after a few minutes. So it seems like its a bad board or just isnt compatible but thats weird because its the same as the old one. Where would the tubes be to check if the lcd is burnt? And ive reinserted the ribbons so many times for a double check its crazy and they seem like there in working order.


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## octaneman (May 13, 2009)

The numbers on the set may match but whats important is the board's serials have to match exactly because the firmware within each board is different. Now, the new board you have now is displaying other issues which the original did not. This is a major concern because the set should have responded in the exact fashion as the original , so its a certainty that the new board is incompatible.


Contact the seller and get your money back.


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## greekoneson (Jul 24, 2012)

There is 2 different numbers. Theres a serial number of course which is a sticker on the back and also a number that resembles the model number heres some pics.


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## greekoneson (Jul 24, 2012)

So it would have to be the serial number that has to match or the one in between the model number and csd number?


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## greekoneson (Jul 24, 2012)

Either way dunno what to do if i cant get a board that matches. Should i try something else maybe get a different tcon board?


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## octaneman (May 13, 2009)

When you test the pin voltages the meter has to be on D/C. If you got 10v from the 5v pins then there is a voltage regulator or diode on the power board that gave out. There are 4 diodes that are bolted on a long ivory colored heat sink which is next to a transformer, these diodes maintain the voltages to the pins, if one burns out the voltages to the other pins will spike above what it should be. Take your meter set it on diode and test each and every one of them, you will need the datasheets for the pin outs their designation is marked on the power board. Please be careful when doing this if you cross your leads or short out the dode pins you will burn out components. 



Question; 


Did you test the voltage coming from the BL_on pin when the set is on its should be 3.3v is the voltage solid or does it fluctuate ?


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## greekoneson (Jul 24, 2012)

It stays at 3.3v and does not fluctuate.


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## octaneman (May 13, 2009)

What about the diodes on the heat sink have you tested them ?


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## greekoneson (Jul 24, 2012)

The black 3 prong ones? They get anywhere from .3 to .16.


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## octaneman (May 13, 2009)

How did you test them ? 

Those 3 black I.C's are duel diodes built in, you set your meter on diode scale , you follow the datasheet pin outs for the annodes and the cathode. Your meter should give you readings in one direction but when the leads are reversed the readings should be infinty. 

Is this what your meter readings are on all 3?


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## greekoneson (Jul 24, 2012)

Here is my meter i set it to the one opposite of the off switch. I dont know exactly what im doing but i reversed and i got readings only on some of them i think 2. Let me know if im doing it right or how to do it and i will try again.


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## greekoneson (Jul 24, 2012)

Im probably driving you nuts but either way i will donate some money to you for all the help.


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## octaneman (May 13, 2009)

greekoneson said:


> Im probably driving you nuts but either way i will donate some money to you for all the help.





I've marked in the picture where your meter settings should be when you begin testing the diodes. Remember, when you do the test the diodes conduct * one way only* when you reverse the leads the meter should read infinty. 

Different meters have ddifferent designations for infinty its either OL or 1 check your meter's documentation.


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## greekoneson (Jul 24, 2012)

I got the red grounded and im using the black to get a reading....the only 2 that give me a reading are the 2 black ones on the heatsink closer to the bottom that are close together....The middle prongs give me around 660 and the top or bottom give me anywhere from 75 too 110 and they seem to drop when there high. I dunno if that tells you anything but let me know if i did it right......if you want i can give you my number and we can do this over the phone if thats ok with you.


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## greekoneson (Jul 24, 2012)

The top 2 black diodes give me readings when the tv is off when its plugged in (standby if thats what you want to call it) but whe turned on it will give inifinite.


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