Vizio VT470M Intermittent BSOD (no picture, no sound)

[solder1]

Hello All,

Before I get into the issue, I will say that my knowledge about electric circuits is not all that good. I understand positive, ground and fuse. When I get into capacitors, resistors, heat sinks and etc, I am on pretty shaky ground. I have a multi-meter and a soldering iron for tools, but that is all I have for testing and repairing.

On to the issue:

I have a 4(ish) year old Vizio VT470M LCD tv. About a week ago I turned it on and I *thought* I heard a small click or pop (but not certain about it). Of course it did not turn on. The standby light lit up but I got no picture and no sound.

Of course I took it apart and started searching the internet and it seems that this forum is the place to be for any real good information. I have read through many threads here, but none seem to really hit every issue that I have. I do not see any obvious dark spots or capacitor bulges.

I have uploaded pictures and I hope that my terminology is acceptable but if it is not, please correct it as you respond. I have labeled the connections in the pictures that will have corresponding volt readings in this post.

Regarding the volt readings, I could not get them to format as well as I would have liked, but I hope you are able to read them. The first column is the PIN then a "-" and then the reading with 'power off' and then another "-" and then the reading for 'power on'. At no point does the "-" imply negative.

I will start with connection "A" on the power supply:

PIN power off power on
____ ________ ________
5V - 5.4 - 5.2
5V - 5.4 - 5.2
ps_on - 0 - 4.9
24V - 0 - 24.9
24V - 0 - 24.8
gnd - 0 - 0
gnd - 0 - 0
gnd - 0 - 0
12V - 0.4 - 13.1
12V - 0.4 - 13.2
dim - 0 - 4.1
on/off - 0 - 0.2

Moving on to "B" on power supply (which feeds master):

pin power off power on
___ ________ ________
dim - 0 - 3.7
on/off - 0 - 0.1
*open* - - - -
gnd - 0 - 0
gnd - 0 - 0
gnd - 0 - 0
gnd - 0 - 0
gnd - 0 - 0
24v - 0 - 24.8
24v - 0 - 24.7
24v - 0 - 24.7
24v - 0 - 24.7
24v - 0 - 24.7

And "C" on power supply (which feeds slave):

PIN power off power on
___ ________ ________
*open* - - - -
*open* - - - -
*open* - - - -
gnd - 0 - 0
gnd - 0 - 0
gnd - 0 - 0
gnd - 0 - 0
gnd - 0 - 0
24v - 0 - 24.8
24v - 0 - 24.7
24v - 0 - 24.7
24v - 0 - 24.7
24v - 0 - 24.7

Finally, "D" on the main board picture:

PIN power off power on
_____ ________ ________
brown - 5.26 - 5.25
black - 5.26 - 5.31
white - 0 - 4.95
grey - 0 - 25.0
black - 0 - 25.0
blue (gnd) - 0 - 0
green (gnd) - 0 - 0
yellow (gnd) - 0 - 0
orange - 0.4 - 12.1
red - 0.4 - 12.1
brown - 0 - 3.7
black - 0 - 0 (unsure if this is a ground)

Suddenly tonight, after getting readings on connection "D", I turned the power on and I had a blue screen. I plugged a Chromecast into an HDMI port and changed the input on the TV to HDMI and the Chromecast splash screen was visible. I did not think about playing anything to hear if I had sound unfortunately. I then turned the tv off and back on and nothing but black again.

So it seems intermittent and from what I have read, that may mean a bad solder connection. But would I have (maybe) heard a pop when I turned it one the 1st time I got the black screen?

Any input and ideas on what I should do from here is much appreciated. I am going to go back to trying to get a screen again and check for sound if I get it.

Also, if anyone wants better pictures or pictures of any specific areas, please let me know.

Thank you,
Travis

[budm]

Re: Vizio VT470M Intermittent BSOD (no picture, no sound)

"on/off - 0 - 0.2" The Inverter is not getting the BL_ON (Inv on/off) signal from the main board. you can force on the backligts by disconnecting the ON/OFF PIN to the inverter, then connect a 1K resistor between the ON/OFF PIN on the inverter board and the 5V to force on the backlights.

[solder1]

Re: Vizio VT470M Intermittent BSOD (no picture, no sound)

BudM,

Thank you for your reply. I rechecked the voltage on PS_ON and I got 4.9v consistently. I also get 4.9v at the other end of PS_ON's white wire on the main board. It shows 4.9v and black screen.

I think my "0.2" with power on was a typo at this point.

I don't know if I can edit my original post to reflect that, but I will see. In the meantime, any other ideas?

Travis

[solder1]

Re: Vizio VT470M Intermittent BSOD (no picture, no sound)

I fiddled with the TV again last night.

When I first turned it on, I got a picture. I used that time to hook up a source at an HDMI port and confirmed that I had a picture and sound. The screen was clear and no problems and the sound was fine. I tested the inverter voltages during this time and got within range at all 24V red wire connections. After some time, I powered it off and powered it on again. This time there was not picture, just the black screen. At power on and no picture and no sound, I still had good voltages to the master inverter and to the slave inverter.

I also tested the button switches on the side of the tv (power/input/chan+/chan-/vol+/vol-). I will not list the voltages unless someone thinks it has bearing. I did find it of note that of the four wires (blue.orange,green,yellow) on the connector for the button switch, the blue wire never seemed to have any voltage going to it (through it) whether in power on or power off. All the wires lead to an input on the main board. The other 3 wires had 3.2V. I am also attaching pictures of the switch to this post.

I still feel it is a cold solder joint but I don't know what I am basing that on other than it works until it warms up. But it seems to work UNTIL I shut it off. It does not 'go out' on its own.

Anyone have any ideas on where I should go from here?

Travis

[solder1]

Re: Vizio VT470M Intermittent BSOD (no picture, no sound)

Can anyone explain in detail how to pull the pins so I can force the BL_ON? I have a 1K fuse, but a little more specifics would be appreciated. Also, if I can in fact force the backlights on, what does that mean? What is the underlying cause? Or at least can we narrow down what board is the culprit (main or ps)?

Travis

[tom66]

Re: Vizio VT470M Intermittent BSOD (no picture, no sound)

Disconnect the connector between power board and main board, leave it connected at power board end. Run a 1k resistor between the ON/OFF and 5V standby pins, and one between the PS ON and 5V standby pins. The backlight should then turn on, but the image will be blank (full white or black.)

[solder1]

Re: Vizio VT470M Intermittent BSOD (no picture, no sound)

I had some 1K (1/2 watt) resistors, so I jumper the positions indicated. Please see attached pictures.

After jumpering, I got 5.48 Volts on the yellow wire where it leaves the PS board and 5.48 Volts where the yellow wire enters the master inverter.

I did not get a backlight as far as I could tell. I held light up to screen but did not see anything.

Travis

[tom66]

Re: Vizio VT470M Intermittent BSOD (no picture, no sound)

You need to jumper PS ON not DIM.

[solder1]

Re: Vizio VT470M Intermittent BSOD (no picture, no sound)

Sorry, I uploaded the wrong picture. Attached is correct (I think). I checked volts again just to be sure and my previous post is correct as far as volts, no backlight. However I could hear a faint "click...... click..... click....." .

[solder1]

Re: Vizio VT470M Intermittent BSOD (no picture, no sound)

The click noise seemed to be coming from the PS board by the way.

[solder1]

Re: Vizio VT470M Intermittent BSOD (no picture, no sound)

I replaced the power supply board today. No change. Anyone have any ideas on where to go from here?

[uncleb75]

Re: Vizio VT470M Intermittent BSOD (no picture, no sound)

I have found that in the 8pin connector on the main board, the black on/off wire (if removed from the harness) will allow all backlights to come on. If i re-apply the wire, the screen goes all black (no backlight). I slightly bent the main board from the bottom and tried to turn it on with all pins connected and found the tv to work.once i tried to screw it back on the chassis, it turned off. I have a family member that has been fixing for years (unfortunately out of state) but advised me that it was a bad solder. if you can get the tv to turn on and work, then the components are fine. the intense heating and cooling over time ruins the solder. Take a pencil and start at the bottom left (because i have the same problem as you ) and slowly move things around with the tv face down on the ground and it loud enough to hear it. Keep doing a "grid" search to find the bad solder. he advised to use jewelers glass to try and see it.

[johnboy1313]

Re: Vizio VT470M Intermittent BSOD (no picture, no sound)

Cold solder is a strong possibility. So is the chance that a wire terminal inside the plug has bent a little causing a bad connection. Have you tried wiggling the wire harnesses to see if it makes a change?

[solder1]

Re: Vizio VT470M Intermittent BSOD (no picture, no sound)

Uncleb75 and Johnboy1313,

I have tried wiggling the wires, but nothing happened. But I do not think that I have ever focused on the 8 pin main board connection. I will try messing with the MB-PS connection tonight and see what happens.

Thank you,
Travis

[solder1]

Re: Vizio VT470M Intermittent BSOD (no picture, no sound)

I have found that in the 8pin connector on the main board, the black on/off wire (if removed from the harness) will allow all backlights to come on. If i re-apply the wire, the screen goes all black (no backlight). I slightly bent the main board from the bottom and tried to turn it on with all pins connected and found the tv to work.once i tried to screw it back on the chassis, it turned off. I have a family member that has been fixing for years (unfortunately out of state) but advised me that it was a bad solder. if you can get the tv to turn on and work, then the components are fine. the intense heating and cooling over time ruins the solder. Take a pencil and start at the bottom left (because i have the same problem as you ) and slowly move things around with the tv face down on the ground and it loud enough to hear it. Keep doing a "grid" search to find the bad solder. he advised to use jewelers glass to try and see it.

Thank you. I will have a go at that tonight and let you know what happens.

Travis

[uncleb75]

Re: Vizio VT470M Intermittent BSOD (no picture, no sound)

just an fyi, i put a thick rubber "o" ring between the main board and chassis on the bottom 2 screws. my tv has worked everytime i turned it on so far, and its been 3 days. I guess the pressure placed on the board is forcing the bad connection together.

[solder1]

Re: Vizio VT470M Intermittent BSOD (no picture, no sound)

just an fyi, i put a thick rubber "o" ring between the main board and chassis on the bottom 2 screws. my tv has worked everytime i turned it on so far, and its been 3 days. I guess the pressure placed on the board is forcing the bad connection together.

Uncleb75,

Well, I wish I had better news.... but I pulled the black pin and turned it on and got nothing. I then flexed the main board along 2 axis (while black was disconnected) and got nothing. I then plugged the black pin back into the 8 pin connector and flexed the board and got nothing. I then went poking and prodding at various components with a marker (didn't have a pencil) and got nothing.

I am tempted to take the main board off and just start "re-melting" any solder joints I can see.

Travis

[uncleb75]

Re: Vizio VT470M Intermittent BSOD (no picture, no sound)

well keep me posted on your progress. Are you still getting picture until it warms up?

[solder1]

Re: Vizio VT470M Intermittent BSOD (no picture, no sound)

well keep me posted on your progress. Are you still getting picture until it warms up?

No, I am not getting a picture anymore at all. I was able to get it a couple times, but it has been a while.

I will let you know what I find out and thanks for the help.