Vizio V042L Completely dead!

[XmouseX]

Hello all! I am real stuck on this one. I have Vizio V042L that will not Power and has no voltage what so ever coming out of the PS board. Not even standby voltage. I have checked all fuses. I know it isn't the main board, because the voltage is not even making it that far. I have replaced the rectifier(even though it tested good.) I have replaced the Q801 (part#15N60C3) even though it tested good. I am lost at this point. I cannot see any physical failures either. Please help. Thanks!

[XmouseX]

Re: Vizio V042L Completely dead!

Also noticed that I am getting voltage throughout the primary side of the board and nothing on the secondary...

[budm]

Re: Vizio V042L Completely dead!

Do you get 160vdc right at the two legs of that large filter cap?
Straight shot pictures of both top and bottom side of the board, also in 1/4 section or smaller pictures of top and bottom so I can see the traces and component on the board.
Make and model of this power supply?

[XmouseX]

Re: Vizio V042L Completely dead!

I will get those for you for sure. Thanks Budm

[XmouseX]

Re: Vizio V042L Completely dead!

Ok so I hope I took these pictures right. Here is the crazy thing. I do not have DcV on the capacitor legs. I do Have 62.5 AcV though....

[XmouseX]

Re: Vizio V042L Completely dead!

Vizio 0500-0507-0520 Power Supply --- sorry forgot that

[budm]

Re: Vizio V042L Completely dead!

"62.5 AcV though" That reading is wrong because you are using the Chassis safety ground as the Ground ref point. For the incoming AC measurement, you will read the AC voltage at the Line(Black or Brown) and the Neutral wire (White or Blue) which should read 120VAC. When you work in the primary side DC voltage checking, the Negative leg of that large filter cap will be the primary side circuit ground ref. point for the voltage measurement.
Since you do not have the DC at the main filter cap, I will need to trace out the connection from the AC input to the Bridge rectifier to the filter cap. The main fuse is good for sure, right?
I will download the pictures and make some test points for you to test, it will be awhile.
By the way, did any body else work on this TV before it went out and did it go out all the suddenly?

[XmouseX]

Re: Vizio V042L Completely dead!

Yes the Main fuse is reading 115 Vac on both sides. So I can measure voltage on the large cap with negative probe on negative leg and positive on the positive leg?

[budm]

Re: Vizio V042L Completely dead!

Yes.

[XmouseX]

Re: Vizio V042L Completely dead!

Ok so on the large cap i measured 0.9Vdc but it was steadily climbing about .01V every second.

[XmouseX]

Re: Vizio V042L Completely dead!

This TV has never been worked on. It just turned off by itself and stopped working. No power at all.

[XmouseX]

Re: Vizio V042L Completely dead!

Ok so I decided to check out those little blue caps around the board and I found 2 that tested bad. They all tested 1.325nF except for the 2 circled. They seemed like they would start to charge, then fluctuate and drop a bunch.

[XmouseX]

Re: Vizio V042L Completely dead!

Ok so this is weird. I replaced those Caps with good ones from another vizio board. NOW I have 157 Vdc on the large cap! Same problem though

[budm]

Re: Vizio V042L Completely dead!

That is just a coincident since those blue caps (x/y safety caps with very low value) are for noise filter, they can all be removed and the power supply will still functioning without them in place. Since now you do have the 160DVC on the cap, try flexing the board to see if the 160V will go away.
The 1.325nF is = .001uF (the 0.325 may be just the meter error) which is about right for the cap between the Line and the chassis ground, the value should be low since we do not too much AC current flowing into the safety ground.

[XmouseX]

Re: Vizio V042L Completely dead!

Ok I get voltage at the large cap no matter what I do. Still no voltage on the secondary.

[budm]

Re: Vizio V042L Completely dead!

Ok, I will have to trace out the standby power supply section next. I did not really have the chance to look at all the pictures yet to see if they are usable or not, it will be sometime tomorrow before I can dig deep into board layout, it is getting late here for me right now, will continue tomorrow, Tom from England may come on line soon, he may be able to look at the pictures also. G.night for now.

[XmouseX]

Re: Vizio V042L Completely dead!

Good night! Thanks budm

[XmouseX]

Re: Vizio V042L Completely dead!

Update.! Looked around a bit more and found this. C909 blew out its bottom. Also the Mosfet right next to it Q905 was very black on the lower corner. There was big black burn mark on the heatsink. I replaced C909 and retested with same problem. I am thinking Q905 may have failed, but not quite sure how to test it.

[budm]

Re: Vizio V042L Completely dead!

C909 looks to be part of the snubber circuit, you can check the MOSFET if it has Source to Drain shorted out or not, that cap is also high voltage rating cap.

[XmouseX]

Re: Vizio V042L Completely dead!

There is no short from Source to Drain. Seems to work correctly.... Still lost