Dead Vizio VL 420M

[CapLeaker]

Re: Dead Vizio VL 420M

So you got a main board issue.

[budm]

Re: Dead Vizio VL 420M

One thing I do not know on this unit is the ACD signal (AC Detect), I do not know if it is normally HIGH or normally LOW.

[Tayninh55]

Re: Dead Vizio VL 420M

Thanks to all of you for your instructions! Now, where do I go from here? I wonder why the set came on temporarily the way it did, and with a perfect picture (No Signal) on the screen? I turned it on and off several times, and it remained perfect each time, until it went off for the last time. Also, the yellow logo to white logo (when on button is pressed) still seems to be working, which it wasn't before at all, even though the screen doesn't lite up. This all happened instantly when I had the black lead on chassis ground, and then touched the red lead to (my number 5 pin on the smaller connector) the ON_OFF INVERTER. I did nothing else, and as the set is resting on the top of my pool table, nothing could have even moved as I was doing this. Another question, since all of this happened at the same time, why did the logo light not stop working again as it was in the beginning? Really appreciate your help!

[Tayninh55]

Re: Dead Vizio VL 420M

Budm & Capleaker,,,,,,,,Since I have received no more replies to my thread, I guess I certainly was wrong when the picture came on and I thought I was getting lucky! Do you think I will be able to change a component on this board and fix it? Do you think I will have to get a replacement DPS-260JP A main power board to take care of the problem? Do you think the replacement board will solve my problem? Thanks!

[CapLeaker]

Re: Dead Vizio VL 420M

On a second thought: look at the backside of the power supply and look for cold solder joints, also look at the pin connectors. Once you got squared away, leave the main board disconnected and force the power supply and the backlight on.

[Tayninh55]

Re: Dead Vizio VL 420M

Cap,,,,,I know how to look for cold solder joints, but how do I "force the backlight on? What you mean is to disconnect the 6 pin and 12 pin connectors going to the 2nd board, and then turn the power on? The logo light shouldn't come on then because the on/off switch will be disconnected? Once I plug the 120V back on,,,,,how do I force the back light on? Guess I'm really a big dummy!

[CapLeaker]

Re: Dead Vizio VL 420M

Well... sounds like something is intermittent. But what? Anyway... here we go:
Unplug the ribbon cables going from the power supply to the main board. The only thing on the power supply that stays plugged in are the back lights. Now take a 1k ohm resistor from PSon to 5V Standby and another 1k ohm resistor from BLon (I think it is inverter on in your case) to 5V Standby. Plug the baby in and all the voltage rails should be up on the power supply and the backlight should be on as well. Now you can test nicely the output rails, let her rip and give her a few cycles as you wish. Hopefully the power supply never misses a beat. We are totally isolating PS and mainboard, "forcing" the PS manually on. As usual: Really watch what you are doing around the primary.

[Tayninh55]

Re: Dead Vizio VL 420M

I guess it doesn't matter which of the three standby pins I use? Ok,,,,,I'll give it a try and see what happens! Might be awhile before I get back to you on this, and thanks again!

[Tayninh55]

Re: Dead Vizio VL 420M

I guess it doesn't matter which of the three standby pins I use? Ok,,,,,I'll give it a try and see what happens! Might be awhile before I get back to you on this, and thanks again!

[Tayninh55]

Re: Dead Vizio VL 420M

I'm getting ready to solder in the resisters, but before I do, I have another question. Probably doesn't have anything to do with my problem, but do these look like they've been "hot", or do most just look like this?

[budm]

Re: Dead Vizio VL 420M

I cannot tell from the picture if the inverter transformers were over heated or not.
What you can do for now is to force on the power supply first, no need for BL-ON force on yet, to see if the PFC Voltage is working or not first.
The Voltage on the main filter cap should go up to >360VDC, if it does, then you can do force the bl-on to see if the backlights will come on.

[Tayninh55]

Re: Dead Vizio VL 420M

Cap, it didn't "blow up"! budm,,,,,too late, I already did the BL-ON force! The BL came on,,,,,,,should I still check the main cap for voltage, while the resisters are in place? What should I do next?

[CapLeaker]

Re: Dead Vizio VL 420M

Did you check all the voltages? Try this setup a few times. No need to check the filter cap. PFC is working, otherwise you wouldn't have back light.

[Tayninh55]

Re: Dead Vizio VL 420M

Well, I've left it on steady for about an hour and a half and the back lights are still going strong!

[Tayninh55]

Re: Dead Vizio VL 420M

Cap, Do you mean "check all the pins again", while the resistors are hooked up?

[Tayninh55]

Re: Dead Vizio VL 420M

Ok, I presumed you did want me to check voltages on the pins so here is what I got. I really couldn't get a reading on any of them. On the twenty vdc range, with blk lead on chassis gnd, and red lead on the pin, none would hold a steady voltage, they all jumped from .01, .02, .03, .04, and then back to zero, then started over again. The only one that was any different was the DIM pin. When I touched this pin with the red lead,,,,,,,,,,,,,the back lights would blink off.

[CapLeaker]

Re: Dead Vizio VL 420M

Like post 18. Lets see that all voltages that are there are good. Let her run some more, turn it off and on as you please. Anyway... I still think the problem is the main board.

[Tayninh55]

Re: Dead Vizio VL 420M

When you say "Main Board", you are talking about "this board" aren't you, the one where the power cord plugs into? OK, I'll type it out for you!

[CapLeaker]

Re: Dead Vizio VL 420M

no. that is the power supply. the main board is the other one with the HDMI, RCA jacks etc. (post #3). I just want to make sure that the power supply is good.

[newtothis]

Re: Dead Vizio VL 420M

Main is one with inputs like RF and HDMI etc

EDIT ***Got there before me Cap ***