Dead Vizio VL 420M

[nomoresonys]

Re: Dead Vizio VL 420M

maybe touch up any joints that look suspicious.

[CapLeaker]

Re: Dead Vizio VL 420M

Force it on again with the main board disconnected

[budm]

Re: Dead Vizio VL 420M

Thanks Bud & Cap,,,,,,,,,,,,,,,,,,but I haven't been able to get the dang thing back on!

Well, is the PS_ON still present? 5VSTB present? that is why I ask you to check the signals when it is not working, this is getting tired.

[Tayninh55]

Re: Dead Vizio VL 420M

Budm,,,,,,I know this is getting awful tiring,,,,it is for me too. I am not an electronics expert, just trying to fix this tv for relative to save him money. I know from the past that you must be very good at this, perhaps you were trained to do this, since you give “lots of people” “lots of help. I am 68 yrs old, a Vietnam Vet. I was a machine operator in a glass plant and worked there for over 20 years making bottles as small as blood specimen bottles to gallon jugs. After the glass plant closed down (as they did all over the country) I went to work in a paper mill making paper. I could make a pretty good bottle, how good are you at making glass bottles. I have been retired now for a while and had been enjoying fooling with this stuff. I don't want to “piss you off” and have you ban me from your board,,,,,,but you surely know how it makes me feel when you make sarcastic remarks about me, when I'm trying to do something that I'm not very familiar with, and doing the best I can. I'm sorry for making so many posts, and I'm sorry that I don't always understand what you mean when you ask me a question,,,,but I'm trying, and I do appreciate all your help! Again, sorry for the long post.

Capleaker and Budm,,,,,,,,,I tried everything I could think of to emulate what I did when the “tv came on for me” before. I wiggled the wires, and wiggled the power board,,,,,,but nothing would make the back lights come back on! Cap, I just read your post a few minutes ago about trying to “force the back lights on” again. I had already done that about an hour ago,,,,,,,,and they came on but that was all, so I just left it that way. I came in here and read your post about disconnecting the main board and forcing it again. I thought “Oh no, I screwed up again, because I forgot to disconnect the main board and didn't know what effect it would have on it. I went back down,,,,,,,,,and the picture had “come on” again while the resiters were still in place. I removed the resisters, since I had gone into the plastic connector from the top this time, and only needed to pull out the wires. When I removed them, everything stayed the same, and I now have a picture again.

Budm, since yesterday, you mentioned that I should have taken voltage measurements while the tv was working, I did so today. Below are the voltage readings with the tv working and a picture on the screen;
12_Pin_ Connector
Pin…. 1………+5vsb………….5.18
Pin….2……….+5vsb………….5.18
Pin….3……….+5vsb………….5.18
Pin….4……….SGND…………..0
Pin….5……….SGND……………0
Pin….6……….SGND……………0
Pin….7………..SGND…………..0
Pin….8………..SGND…………..0
Pin….9………..12V………………12.36
Pin….10………12V….…………..12.36
Pin…..11……..12V……………….12.36
Pin……12…PS_ON………………...0.59


6_Pin_Connector
Pin……1…….ACD……………………..…….0.06
Pin……2…….Lamp_Status………………0.06
Pin……3…….DCR……………………..……..0
Pin……4…….VBRA……………………..……0
Pin……5…….ON_OFF_INVERTER……2.20
Pin……6…….DIM……………………………2.81

What do you think I should do now??????

[Tayninh55]

Re: Dead Vizio VL 420M

Well,,,,,after typing out that post and submitting it, I went back down to check on the TV,,,,,,,,,,,,,the screen is black again, and no back lights. It still has the white logo. Nobody touched it and it is sitting on top of a pool table on a basement cement floor.

What could have happened for it to go out like that?

[CapLeaker]

Re: Dead Vizio VL 420M

Umm something isn't right. With the PSon sitting on 0.59v, the power supply should be off, and only the 5 STBY a should be running (it's on all the time).

[CapLeaker]

Re: Dead Vizio VL 420M

At least you know know how to quit and start it again

[budm]

Re: Dead Vizio VL 420M

"Pin……12…PS_ON………………...0.59" if that reading is VALID, then I would check that pin on the board, the wire attached to the terminal which inserted into the connector, the PS_ON pin on the main board side.

[Tayninh55]

Re: Dead Vizio VL 420M

Well then, thanks Cap & Budm. I wasn't sure how exactly you wanted the Pin #12 (PS_ON) checked out so I did a bunch of stuff, see if any of it is useful.

***I'd noticed this before, but hadn't mentioned it, but the aluminum shield over the capacitors right behind the ribbon connectors, shows .05V when checked to ground with the yellow logo on, and still there when the white logo is on. I checked all the other shields, and none show voltage. Don't know if this is something that could make a difference or not.

With Power Off (unplugged) and no back lights
I checked the continuity of the ribbon cable for Pin 12 from end to end (not connected), and it was ok.
I checked the continuity of the wire running from pin 12, from it's connection at the main board to ground, and it showed to be ok.
I checked the #12 pin (disconnected from ribbon) to the chassis ground,,,,and it showed BAD. I supposed that it should show continuity to ground at the power board, the same as it did at the main board?

With Power ON (yellow logo) and no back lights
#12 Pin with power on and ribbon cable disconnected shows no voltage.
#12 Pin with power AND ribbon cable connected shows .50V
Wire from #12 Pin at the connection on the main board shows .50V also

With Power On (white logo) and no back lights
#12 Pin at the main board connection shows .52V
Couldn't get the back lights to come on again until I forced it. I left both cables connected to the main board (Is there any problem with doing this?) again when I forced it, and the sound and picture also came on. I left the resisters in place, and the tv has been looking normal ever since. I have not tried turning it on and off,,,or removing the resisters yet.

This is the voltage with the RESISTERS still in place, and picture and sound 12 Pin Connector
+5vsb…………………………………………5.13
+5vsb…………………………………………5.13
+5vsb…………………………………………5.13
SGND…………………………………….……0.02
SGND………………………………………….0
SGND…………………………………………0
SGND…………………………………………0
SGND…………………………………………0
12V…………………………………………..12.31
12V……………………………………………12.31
12V……………………………………………12.31
PS_ON……………………………………….1.65

Voltage on 6 Pin Connector with RESISTERS still in place
ACD…………………………………………….0
Lamp_Status……………………………….0
DCR……………………………………………..0.02
VBRA……………………………………………0
ON_OFF_INVERTER………………………2.94
DIM………………………………………………1.65

[budm]

Re: Dead Vizio VL 420M

No power applied to the TV/Board, pin 12 (PS_ON) should shows resistance in >1000 Ohms.
You said BAD, but without supplying us the numbers then it does not help.

"With Power On (white logo) and no back lights
#12 Pin at the main board connection shows .52V
Couldn’t get the back lights to come on again until I forced it. I left both cables connected to the main board (Is there any problem with doing this?) again when I forced it, and the sound and picture also came on. I left the resisters in place, and the tv has been looking normal ever since. I have not tried turning it on and off,,,or removing the resisters yet." It is not good to force on with the cables (PS_ON, BL_ON) still connected to the main board, it can force too much current through the switched transistors on the main board.
So at this point we know for sure that it is the PS_ON signal is bad because you can force on the TV and it stays working.
So you will need to locate that switched transistor that provides the PS-ON signal on the main board, this transistor gets the ON/OFF control signal from the processor.

[Tayninh55]

Re: Dead Vizio VL 420M

No power applied to the TV/Board, pin 12 (PS_ON) should shows resistance in >1000 Ohms.
You said BAD, but without supplying us the numbers then it does not help.

Maybe it's not bad then, it measures 101 on the 2000K resistance scale.

[budm]

Re: Dead Vizio VL 420M

No it is not bad, it is VERY IMPORTANT to report the readings with more details otherwise it is meaningless.
So start tracing out the circuits on the main board to see where the PS-ON pin is connected to and draw out the diagram.

[Tayninh55]

Re: Dead Vizio VL 420M

budm,,,,,,,On the switching transistor, I think you've got me there. I see a lot of tiny transistors on the main board, but I don't know if they are switching transistors or not,,,,,,and not sure where the one should be located that I'm supposed to be looking for Can see a lot of them near where the ribbon cable connects to the board.

[budm]

Re: Dead Vizio VL 420M

You just have to trace out that copper trace that is connected to the PS-ON post and see where it goes too, that is why it takes years of experience to do this kind of troubleshooting, not for the beginner, you also need to look up the spec sheet of the transistors, ICs to get the pin out, etc.
For example of what I have to do when I do not have the diagram or the board in front of me, this is a simple board. the main board is a lot more complex.
https://www.badcaps.net/forum/showpo...9&postcount=12
So if you are going to pursue this, then expect to spend days or weeks, or months tracing out the circuits.

[CapLeaker]

Re: Dead Vizio VL 420M

We are finally getting somewhere! It is the PSON pin after all. Had a busy day today, just checking quickly up.

[Tayninh55]

Re: Dead Vizio VL 420M

Thanks budm,,,,,I think? MAYBE we'll get somewhere Cap!

[CapLeaker]

Re: Dead Vizio VL 420M

Finding that switching transistor on the main board, may be a real pain. Specifically if you have to trace it out. Good luck with that!

[Tayninh55]

Re: Dead Vizio VL 420M

Trying to get two pics of the board to up load. They are both .jpg's. One is 7,664KB and it will up load. The one I really want to show you is only 2,107KB, it shows it as trying to upload to Badcaps,,,,then the whole box just goes blank.

[CapLeaker]

Re: Dead Vizio VL 420M

Dunno.... There is a limit on the size. It sez so on the upload window somewhere.

[Tayninh55]

Re: Dead Vizio VL 420M

I took a couple pics of the top and bottom of the board, and then enlarged them, been working on them since trying to get them sized right. I circled the PS ON pin on the connector on the top and bottom of the board. budm and Cap,,,,,,,I'm asking, "not telling", but do you think the transistor I circled on the bottom of the board, is the "switching transistor" for the PS ON? I thought it might be, but as you know, I could be wrong!