Vizio Vizio VT420M Good Backlight no sound no picture

[a_eclipse_guy]

Ok, I have spent a few days reading posts about this TV.
It seems as if they are junk..
Long story short here is the prob.

Turn power on at the switch (no remote) The "Vizio" logo on the frame turns a faint amber color and fades out. The backlight come on and then off for a sec and back on and stays on. There isn't any display at all.

Not sure what the board is called that sends signals to the screen was swapped out with no change.

I have checked the power supply everything seems to check out. Voltages going in and out of it (all caps look good) etc..

I did check voltages at the reg (U702) Counted pins with the tab up and counted left to right.

Pin 1 0.00 volts
Pin 2 3.297
Pin 3 5.12

Are these correct voltages?

Before I spend any cash on this tv I would like to know how to check to see if the screen is ok before I replace boards etc etc etc..


Thanks
Kenneth

[budm]

Re: Vizio Vizio VT420M Good Backlight no sound no picture

That is correct, it is 3.3V regulator. I expect the board to have more than one regulator.
Do you get either 5 or 12v at the T-CON fuse?

[a_eclipse_guy]

Re: Vizio Vizio VT420M Good Backlight no sound no picture

Yes, I do have 12V at the T-CON fuse.
The power will also drop to 0.0 and back to 12 with the on/off thing the backlight does...

There is one other reg that I found on the board (u701)it is missing pin#2 on it.
Pin#1 11.28
Pin#2 Stub 0.00
Pin#3 9.07

Only 2 regs that I see on that board.
If it matters this board is different than any of the other ones I have seen on any site so far.
I was thinking it might be the board. However, I read somewhere where someone said to disconnect the cables from the T-con board and watch the screen for changes. Tried and the screen doesn't change at all.

[budm]

Re: Vizio Vizio VT420M Good Backlight no sound no picture

That may be 9V regulator. Do you have the number as printed on it. At this point you will need the new main board.

[a_eclipse_guy]

Re: Vizio Vizio VT420M Good Backlight no sound no picture

It has 17809 printed on it.

[budm]

Re: Vizio Vizio VT420M Good Backlight no sound no picture

OK, that is the same as LM7809, positive 9V regulator.

[a_eclipse_guy]

Re: Vizio Vizio VT420M Good Backlight no sound no picture

So I guess I am looking at a board......
What are the odds that it could be a prob with the screen its self?
I don't really want to drop 200.00 for a new one.
Would it be more cost effective to have it repaired?

[retiredcaps]

Re: Vizio Vizio VT420M Good Backlight no sound no picture

Only 2 regs that I see on that board.

Sometimes, the main board has components on the backside.

[a_eclipse_guy]

Re: Vizio Vizio VT420M Good Backlight no sound no picture

I didn't find anymore on the board. Does anyone know of a way to test the panel(screen) to find out if it is good or not?

[JonathanAnon]

Re: Vizio Vizio VT420M Good Backlight no sound no picture

Turn power on at the switch (no remote) The "Vizio" logo on the frame turns a faint amber color and fades out. The backlight come on and then off for a sec and back on and stays on. There isn't any display at all.

Maybe a video or pictures of this would be helpful..

[a_eclipse_guy]

Re: Vizio Vizio VT420M Good Backlight no sound no picture

I did find one more reg on the back of the board.
Pin1 .008
Pin2 Stub 5.00
Pin3 9.03
I guess it is working correctly.

[Cosmo66]

Re: Vizio Vizio VT420M Good Backlight no sound no picture

I'm dealing with this same model, exact same issue. It seems to be a common problem with this model, as I've noticed on other threads

Backlights come on, power supply voltages are all good. Already changed T-CON. No signal, audio or video. Sometimes it stays on. Sometimes shuts off.

I'm thinking this is an eeprom issue.

The strange thing is that I've removed and reinstalled the main board a few times to resolder joints. Everytime I do this the TV will work afterwards, I'll think I fixed it until later when I go back and turn it on, the problem returns.

To get it working again, I have to unplug all connectors on the main board, wait a while, and will work for a while again. I've tried to just play with the connectors, thinking one of them is bad or loose, but this never changes anything. I have to actually remove the connectors for a while. I know this sounds ridiculous to anyone with any actual electronics knowledge

I'm thinking maaaaybe one of the caps on the psu is holding some voltage to the main board, possibly keeping the jacked-up eeprom in some weird state......??/?

I don't know I guess the only way to find out is replace the eeprom. I'll report back to this thread after I change it.

[a_eclipse_guy]

Re: Vizio Vizio VT420M Good Backlight no sound no picture

So I have been bored and started playing around with this TV again..

I unplugged the LDVS cable from one side and that side of the screen turns white. Same with the other side. So would I be looking at the Tcon or a mainboard.

One thing I did was hookup audio to the set and switched the menu button to scroll through inputs. Didn't work...

[philliesfan30m]

Re: Vizio Vizio VT420M Good Backlight no sound no picture

as budm stated earlier in the post that you would need a new main board i would say he is right because he is right more often than not about what to replace on tv's. and if you already changed the t-con to no avail then that is the only other board to replace that could possibly fix the problem you are having.