Vizio M492i-B2

[BobbyG58]

I am working on this tv. The TV will display the Vizio Logo fo a few seconds and then the TV goes Black and the power light will slowly blink.

I have standby power and I have voltage to the driver board attached to the Power Supply.

There are virtually no pin out voltages on these boards except on the PS board.

Here is my thinking, since the Display is fine when it displays the Logo on screen, it leads me to believe that power supply is good, the driver board is good, the T-Con is good since all fire up after fully discharging the unit.

I have checked the connector points for cold solder joints on the connector from the PSU to the driver board. All the connectors on the driver board that I can test with the board installed have voltage however the connector from the main board is is in question since there are no pin voltages on the boards. I have also unseated and reseated all connectors.

This leads me to think that it is the main board.

[budwich]

Re: Vizio M492i-B2

disconnect, one at a time, the tcon to panel cable and see if anything changes.

[BobbyG58]

Re: Vizio M492i-B2

disconnect, one at a time, the tcon to panel cable and see if anything changes.

Once I do that, what can I expect to see? No Change would indicate what? Or if there is a change what might I see?

I forgot to mention in my original post, after the set has fully discharged and I plug the set in, the set begins to power up and displays the Vizio logo on screen for a couple seconds, screen goes black and the power led begins to slowly flash.

At this point I see on two pins from the power board to the driver board 24V. I don't fel comfortable trying to test the other pins on that connector due to the pins below the top pins. Don't want to accidentally touch both upper and lower pins. My test leads have needles soldered to the ends for other testing I do on phones and tablets. then on the driver board I see the various Voltages to the LED connectors but no pin out voltages are available.

On the driver board connector from the main board there are no voltages.

[R_J]

Re: Vizio M492i-B2

I would suspect some bad led's in the panel myself, it only take one or two to shut the led power supply down, 24 volts supplies the board and there are two voltage regulators for the led's. The voltage is likely low around 20 volts as the caps are only rated at 25 volts.
Without knowing how many led's are on each string its hard to guess the voltage to each but you could check each line to see if one is way off from the others.
You will need to monitor the line, then turn on the tv to see what the voltage is as it will error and shut down

[BobbyG58]

Re: Vizio M492i-B2

I would suspect some bad led's in the panel myself, it only take one or two to shut the led power supply down, 24 volts supplies the board and there are two voltage regulators for the led's. The voltage is likely low around 20 volts as the caps are only rated at 25 volts.
Without knowing how many led's are on each string its hard to guess the voltage to each but you could check each line to see if one is way off from the others.
You will need to monitor the line, then turn on the tv to see what the voltage is as it will error and shut down

I would love to try checking those pins with the set on, however, it appears than when the screen goes blank, it goes into standby. When I check the four connectors while in this state, I get varying voltages from about 1.5v, 3V and up to 12V on the upper pins on all four connectors driving the LEDs that I can test. I cannot get on the lower pins.

I cannot get to the point of testing those connectors fast enough since it shuts down in about two seconds.

The owner said that it started out with shutting down and then they could restart it, then it got to the point it is now.

When the set does fire up to the Vizio logo, it does not appear that any LEDs are weak but it is hard to say since it shuts down so quickly.

It is frustrating since there are no pin out voltages except on the PSU.

[R_J]

Re: Vizio M492i-B2

will the tv come on with the multicolored wire cable between the main and led driver board disconnected?
Have you tried disconnecting one of the cables that feed the led's, does it make a difference?

[BobbyG58]

Re: Vizio M492i-B2

will the tv come on with the multicolored wire cable between the main and led driver board disconnected?
Have you tried disconnecting one of the cables that feed the led's, does it make a difference?

I tried disconnecting the connector from the mainboard to the driver board with no change.

I will try disconnecting one LED connector at a time from the driver board and see what happens.

Thanks.

[R_J]

Re: Vizio M492i-B2

Based on the amount of backlight led's that drop dead versus boards, I would suspect the backlights, But if you want, shopjimmy has the led driver board for $17.48, the fact that they have it tells me its not a common failure.
CN901 is the control line so you would likely need a scope to view the signals.

They usually apply the (+) voltage to one end of the leds and control the return (-) lead, that is where they also monitor the current drawn by the string, so too much current, ie one or two shorted led's or no current drawn IE open led will shut down the drive ic.

In this https://www.badcaps.net/forum/showth...492I-B2&page=2 thread, looks like the main board caused the problem???

[BobbyG58]

Re: Vizio M492i-B2

Based on the amount of backlight led's that drop dead versus boards, I would suspect the backlights, But if you want, shopjimmy has the led driver board for $17.48, the fact that they have it tells me its not a common failure.
CN901 is the control line so you would likely need a scope to view the signals.

They usually apply the (+) voltage to one end of the leds and control the return (-) lead, that is where they also monitor the current drawn by the string, so too much current, ie one or two shorted led's or no current drawn IE open led will shut down the drive ic.

If, as you mentioned that one or more and I pull one connector at a time, would the set power up with one connector pulled from the circuit leaving the screen with a dark side/ spot or will pulling one just shut it down?

[BobbyG58]

Re: Vizio M492i-B2

I just got back from the shop. I tried unplugging one led connector at a time at the driver board, no change, tried unplugging the Panel cables from the main board to the T-con one at a time, no change. The set now does not fire up at all, just goes straight to blinking power led. This maybe because the set has not fully discharged.

I have read on other Vizio sets that the blinking power LED can indicate bad Main board. I am lost without any pin out voltages.

[R_J]

Re: Vizio M492i-B2

Re check the plugs you removed, You did not unplug the cables with the tv on I hope, I see no reason why unpluging the tcon would cause any issues.

[BobbyG58]

Re: Vizio M492i-B2

Re check the plugs you removed, You did not unplug the cables with the tv on I hope, I see no reason why unpluging the tcon would cause any issues.

LOL, yup, I know not to plug and unplug while powered up and without trying to discharge everything with the power button. Unplug power up. Shut down, discharge, plug back in, unplug the next one, power up until I tried every connector on the set.

The same on phones and tablets. I hate those videos of people tearing into a device without disconnecting the battery. That is especially true on Apple devices.

I am really leaning to going with my gut instinct and guess that the main board is not telling the driver board to power up based on the other link you sent and with the limited voltages that I can see and the other article on the blinking power led on the set.

Without pin out voltages or a schematic, it's all a guessing game at this point.

[BobbyG58]

Re: Vizio M492i-B2

UpDate: Replacing the Mainboard did the trick.

Thanks everyone for the help and ideas.