Vizio E550VL turns on no backlight no audio

[danman282]

Hi everyone, I have a vizio e550vl that I picked up.When I got the back panel off there was obvious damage to the master 1 & 2 inverter boards. The cable that connects them had melted and there were long brown marks on each board. I'm still a rookie when it comes to TV repair so I replaced the two boards all together. When I plug the TV in the standby light comes on and I here a couple clicks. When I press the power button the TV clicks on, the Vizio light turns white, but there's no backlight or nothing. I have tested the fuses.

I have learned a lot and done some tests. There are no obvious signs of damage to caps or IC's. With the TV on I get the 5vsb. I'm only getting 2.88v ps_on and my 12v only has .12v. There is no BL_ON pin.there is no 24v at all. I have tested the IC's on the main board and I believe they are good (within spec.). One is questionable (U8) have to do some more research. The input pin on IC U8 (7805CT) is .12v.

I'm not sure if 2.88v at the Ps_on pin is enough to turn the 12v supply on.
If it is enough volts, is there any idea as to why I only have .12v at the 12v pins?
If it isn't enough voltage, what is a likely cause for the shortage?

Thanks for the help

[Ltank]

Re: Vizio E550VL turns on no backlight no audio

If you disconnect the PS output to the inverters do you get 24vdc? Try to determine if its the master or slave inverter board. Post pics of both boards and the damaged areas.

[budm]

Re: Vizio E550VL turns on no backlight no audio

"One is questionable (U8) have to do some more research. The input pin on IC U8 (7805CT) is .12v" You will have anything on this regulator until the power supply puts out 12VDC. The 12VDC and the 24VDCa re generated by the same circuit and transformer.
First, check the DC voltage right at the 2 legs of the main DC filter cap (450VDC raring) to see if it has 370~400VDC when TV is turn on.
Good clear pictures of the boards also needed.
BTW, there is no sign of damages on the power supply board?
"I'm not sure if 2.88v at the Ps_on pin is enough to turn the 12v supply on" that is fine, >2V = ON, <1V = OFF.

[danman282]

Re: Vizio E550VL turns on no backlight no audio

Thanks for the help. I will try the recommended tests and take some pictures as soon as I can.

[danman282]

Re: Vizio E550VL turns on no backlight no audio

Here's a couple pics. One is of the power supply and the other is the main board. I am still a rookie and I don't know where the main dc filter cap is, but I'm still looking around for info. online. I hope the pics can help you help me.

If you had to guess right now would you say the main board holds the problem?

Thanks again.

[Ltank]

Re: Vizio E550VL turns on no backlight no audio

You said there was obvious damage to the inverter boards. There were not any pics of them. Remove power, wait a few minutes then Disconnect the the cable from the PS to the inverter that are bad. Will the PS turn on? is there 24vdc on the connector that went to the inverters? Use Chasis gnd or ground pin of PS. If PS is not turning on. Remove power. Remove cable from Main board to PS. Jumper the 5vstby power to the
PS_on . Does the PS give any other output voltages? 24?, 12 or 18 for audio to main board?use a 500 to 1000 ohm resistor to make jumper. I the PS gives good voltages.
Recoonect everything except the inverters. Connect HDMI input signal and you have audio, then use a flashlight to look at the screen and you should see an image. This will tell you that the main board, tcon and pannel should be good. Then you can TS the inverters or replace them. Hopefully the backlight bulbs were not the cause of the inverters burning up due too excessive loading.

[danman282]

Re: Vizio E550VL turns on no backlight no audio

I said two were bad and i replaced them both with new boards.

Thanks

[danman282]

Re: Vizio E550VL turns on no backlight no audio

i have also replaced the power supply board and I am still having the same issues. I'm thinking it's the main board which isn't cheap. I have heard that the style of tcon board that I have can cause similar symptoms if it fails. Any truth to that?

[danman282]

Re: Vizio E550VL turns on no backlight no audio

I tested the main dc filter caps (I have 2) with the tv on and they both read 402vdc.

After that I really started tearing into it, to do a really good visual inspection and test any fuses i could find. I found an IC on the Slave 2 inverter with with brown around it and even on the back of the board (see pics). I don't know if it's okay to remount everything without the shields in order to test the IC ?

Even if I were to replace the whole Slave 2 board I don't believe it would fix my problem. I have done the flashlight test and I can't see anything. I have also tried other modes of input.

[danman282]

Re: Vizio E550VL turns on no backlight no audio

burnt slave board IC

[danman282]

Re: Vizio E550VL turns on no backlight no audio

Just wanted to say thanks for all the help. I unplugged the slave boards from the power supply and the backlights came on and have picture now. Have the correct power to everything. One half of my tv is dim cause slave 1 & 2 disconnected, but other than that all is good . Thanks again.