Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

[budm]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

2.89V is enough to bias on the transistor in the power supply PS_ON line. That flickering may be due to the BL_ON and the PS_ON are on at the same time due to the power supply was not steady yet when the INVETER kicks on at the same time, keep an eye on it.

[budm]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

This is what I have the OP do to his Vizio with bad PS_ON control line by using the BL_ON as the PS_ON controller and a delayed circuits for the BL_ON:
https://www.badcaps.net/forum/showth...CIRCUIT&page=2

[MisterD]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

Thanks budm, as always you are a great help to me and I appreciate it. The Vizio logo white light stopped flickering for some reason, I have had the tv up and running for 4 hours and still working with no problems ( processor still about 50 degees C at the most ) I did notice that when I had my DVM hooked up and checking voltage at PSON that when I powered on the tv the voltage was instant to PSON and then backlights come on about 2 seconds later.

[MisterD]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

Tested on/off many times, left tv on several hours at a time with no problems, checked all inputs HDMI,AV, everything worked but I did find a replacement main board on eBay so I went ahead and got it and installed it, re-wired back to normal, working fine. With this board the normal PSON is 2.26 v when tv is on and .06 when tv is off.
The processor temp is about the same with either board (120-125)degrees Fahrenheit.

[budm]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

Thanks for the follow-up on the repair.

[MisterD]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

You're welcome, so now I know that the main board processor heat sink is normally hot to the touch,after I put it all back together with this new main board I noticed that the backlights and brightness were turned up high, so I turned them down some.

I was wondering if the processor works harder with more demand, therefore warmer temperature with higher brightness,contrast and backlights?

[budm]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

I do not believe so, the power supply and the inverter and the lamps will get hotter at high backlights level (not the Brightness control), there should be Backlights brightness level control on the user menu panel.

[MisterD]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

Okay, thanks bud, I'm going to save this old main board for a spare since it worked fine with the bypass and 1k resistor.

[brairicks26]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

MisterD do you have a better picture of how you did the resistor i have a Vizio SV420M and it did the same thing as yours did i wanna see or know exactly how you did the resistor so i can do it

[MisterD]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

Hi brairicks26, Sorry but I don't have a better picture and the tv is gone now, I hope you got yours going.

[kisk]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

Just wanted to say awesome thread and thanks for the bypass insight from both of you!

[ajkirk66]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

Thanks to this thread, I was able to use this same bypass repair to jumper from U7 to PS-ON with 1K resistor to fix a Vizio SV420M 42" TV. I spent several hours trying to diagnose what was wrong with the main board without identifying the culprit. Everything checked good from capacitors to voltage regulators to diodes etc. I was getting pretty frustrated until I saw this thread. This solution got me up and running in a matter of minutes! It cost me $1.69 for the resistor, so I've decided against replacing or repairing the main board. Thank you Badcaps from a TV repair novice!

[102mm]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

This TV is crazy.. are we sure it's the main board.. I have the same issue, I checked my power supply and the 12V is only outputting 1.9V at the connector but the 12V is just fine coming out of the FET. SOmeone help please.