Dead Vizio VL 420M

[Tayninh55]

Re: Dead Vizio VL 420M

When I submitted post 36, it was after my first voltage test. You asked me to retype it, which I did, and here it is for what it's worth;
12 Pin Connector
Pin Number ON
1….+5vsb………………………Reading fluctuates from .00 to .04, over & over………………………
2….+5vsb……………………… Reading fluctuates from .00 to .04, over & over……………………..
3.…+5vsb……………………… Reading fluctuates from .00 to .04, over & over……………………..
4….SGND……………………… Reading fluctuates from .00 to .04, over & over……………………..
5….SGND……………………… Reading fluctuates from .00 to .04, over & over……………………..
6….SGND……………………… Reading fluctuates from .00 to .04, over & over……………………..
7….SGND……………………… Reading fluctuates from .00 to .04, over & over……………………..
8….SGND……………………… Reading fluctuates from .00 to .04, over & over……………………..
9….12V…………………….…… Reading fluctuates from .00 to .04, over & over……………………..
10..12V……………………….… Reading fluctuates from .00 to .04, over & over……………………..
11..12V……………….………… Reading fluctuates from .00 to .04, over & over……………………..
12..PS_ON…………………….. Reading fluctuates from .00 to .04, over & over……………………..

6 Pin Connector
Pin Number ON
1….ACD……………………….… Reading fluctuates from .00 to .04, over & over……………………..
2….Lamp-Status…………….. Reading fluctuates from .00 to .04, over & over……………………..
3….DCR……………………….… Reading fluctuates from .00 to .04, over & over……………………..
4….VBRA……………………….. Reading fluctuates from .00 to .04, over & over……………………..
5….ON_OFF_INVERTER.… Reading fluctuates from .00 to .04, over & over……………………..
6….DIM……………………….… Reading fluctuates from .00 to .04, over & over……………………..

When I was checking the DIM, as I would touch the red probe to it, it would make the back lights go “dim”,,,,,,,,,,,,,,,,,,but after dimming them several times,,,,,,,,,,,it would then “turn them off”. I would have to unplug the cord, then plug it back in before they would come back on.

I think whatever is intermittent was/is in the "power board" but maybe I've screwed that board up more. Seems like something was stopping all the voltage from going to the connector pins after I had forced the backlights on.

After thinking about the voltage readings, I thought they had to be wrong, or something wrong with my meter. I began rechecking them over and over and after about 50 times, all at once I started seeing good readings like:
the three +5vsb ranged between 4.7V and 5.4V, after I saw this, I jumped down to the three 12V pins and they ranged between 11.7V and 12.4V. Before I could check the 6 pin connector, the voltages had reverted back to fluctuating, like I told you before (that's why I think its in the power board, because I actually witnessed the voltage change on my meter). Now to the bad news,,,,,I continued checking, hoping I'd see the voltage change again. This time, after checking the DIM pin, the backlights went out, and wouldn't come back on. I don't know if I touched the solder joint on the ON_OFF INVERTER Pin and the DIM Pin at the same time or what,,,,,but I'm afraid I shorted something. I tried reconnecting the power cord, but it still wouldn't lite back up. I checked the fuse and it's alright, so I'll quit now and check it in the morning. But of all the different times I checked the voltage on the pins,,,,,,,,,only that one time did it look right, and then for just a few seconds.

[CapLeaker]

Re: Dead Vizio VL 420M

Those measurements on top can't be. The power supply can't be on and running and giving these measurements while on. Either the PS was unplugged, you meter is FUBAR, or you had it on a wrong measurement setting, or the battery is dead.

Well I guess something happened since the lights are out. However, you can unplug the inverter board, plug the power supply back in to AC and read the pins again.
I would look for a different meter, borrow or buy one if you have to. Some of the readings that meter is giving is just nonsense and I am starting not to trust it.

[newtothis]

Re: Dead Vizio VL 420M

Those measurements on top can't be. The power supply can't be on and running and giving these measurements while on. Either the PS was unplugged, you meter is FUBAR, or you had it on a wrong measurement setting, or the battery is dead.

Well I guess something happened since the lights are out. However, you can unplug the inverter board, plug the power supply back in to AC and read the pins again.
I would look for a different meter, borrow or buy one if you have to. Some of the readings that meter is giving is just nonsense and I am starting not to trust it.

I agree, I think with a new meter/battery you will see those steady voltages you saw

[budm]

Re: Dead Vizio VL 420M

The Bottom line right now, we have already established that you do have bad main board as the Voltage readings you provided in Post 18, and my post 20.
Now you said the backligts did come on when you were probing the pins, so it is either bad connection on the terminal where the the wires are connected to or on the male post on the board.
Your power supply/invereter board is OK at this point.

[nomoresonys]

Re: Dead Vizio VL 420M

could be bad battery in meter, try testing a aaa or 9 volt battery with it.

[Tayninh55]

Re: Dead Vizio VL 420M

Well, you guys were right, my battery was "pretty well" dead! I evidently didn't short anything out because when I plugged it back in this afternoon, the backlights lit up again! Here are the new readings for the pin connectors on the power board:


12 Pin Connector Backlights
Pin Number ON OFF
1….+5vsb……..5.12V………..0
2….+5vsb……..5.15V……5.25V
3.…+5vsb……..5.15V……5.25V
4….SGND………..0………………0
5….SGND………..0………………0
6….SGND………..0………………0
7….SGND………..0………………0
8….SGND………..0 ……………..0
9….12V……….11.75V……12.05V
10..12V………11.75V…….12.05V
11..12V………11.72V…….12.05V
12..PS_ON….2.70V………2.82V

6 Pin Connector Backlights
Pin Number ON OFF
1….ACD……………………….……….0………………………………..0
2….Lamp-Status……………………0………………………………3.01V
3….DCR……………………….………1.38V……………………………0
4….VBRA………………………………..0………………………………..0
5….ON_OFF_INVERTER.……….2.77V…………………………2.85V
6….DIM……………………….………..2.95V………………………...2.65V

Do these readings make sense to you guys,,,,,,I checked and rechecked about three times. If these readings are ok,,,,,what should I do next. I'm going to remove the 1K resisters and screw the power board back in place since budm said there was nothing wrong with this board. Cap, you and budm both said you're pretty sure it's an issue with the main board, what should I try next? Thanks!

[CapLeaker]

Re: Dead Vizio VL 420M

Well, there isn't too much left to do. There is no short on the 5V STBY line on the main board, so something is either open and no power is going there where it should or the main chip is fried. You could trace it maybe and see how far you get. Check all the little fuses. I can't help you much further right now, the main board pic is too fuzzy to see anything small. A schematic of the main board would come in handy now. Other than that, unless someone else has a better idea and after the fuses don't yield anything, I'd be starting to look and check how expensive a new main board is and way my options.

[newtothis]

Re: Dead Vizio VL 420M

I agree after seeing the voltages off the PSU, Backlights work etc etc

[Tayninh55]

Re: Dead Vizio VL 420M

Well, I just went down, unsoldered the resisters, turned the board over and screwed it in place. I then plugged in both connectors and plugged the power cord in. Turned on the tv,,,,,,,,,,(white logo), but nothing else (no backlights). Wiggled all the connectors on both boards,,,,,,,,,and nothing. So I decided to recheck the voltages without the resistors and see how they looked. I unscrewed the power board and turned it over, plugged the power back on, hit the on button, and still the same, white logo, no backlights. I started checking the voltage on the 12 pin connector first. I got down to where the 12V pins were and stopped. Came upstairs to print out the page I had just posted on here to write down the voltages. When I went back downstairs, I could see the backlights were ON,,,,,,,,,and I had the picture (no signal) back on the screen. Then only thing I had done was insert the meter between ground and the connector pins. This is driving me crazy!

[Tayninh55]

Re: Dead Vizio VL 420M

I've got it FIGURED OUT! I know you won't believe me when I tell you! It was the POWER BOARD!!!!!!!!!!!!

[CapLeaker]

Re: Dead Vizio VL 420M

Cold solder joint? Iam curious now

[nomoresonys]

Re: Dead Vizio VL 420M

I've got it FIGURED OUT! I know you won't believe me when I tell you! It was the POWER BOARD!!!!!!!!!!!!

what exactly fixed it? a different power board? or did you have a bad/dirty connection or something?

[budm]

Re: Dead Vizio VL 420M

Well, according to your post 46, the main board is sending the correct signals to the power supply board AFTER you replaced the bad batteries (after 45 posts) in your meter to get valid readings, so was it bad solder joints on the connectors, traces, etc? We have 52 posts so we would like to know exactly what you found bad on the power supply board.

[Tayninh55]

Re: Dead Vizio VL 420M

Well,,,,,,,,,after 45 posts,,,,,maybe I spoke too soon. This is what I did. After the back lights came on, I decided to turn the power board over and fasten it down. As soon as I did that, I lost the backlights again. I went through the whole routine again, moving things, wiggling the wires and connections, pulling and pushing on the wires going down into the connectors,,,,,,,,,nothing worked. I had already taken all the screws except two out of the power board mounting, leaving one in each corner, when for some reason, I put my finger on the edge of the board (where the arrow is), and lifted slightly (maybe a sixteenth or eighth of an inch) on the board. Every time I would raise the board, the backlights would come on let it go back on the mounting spot and they would go out,,,,,I did this about a dozen times with the same results. I thought the board was grounding out where it attaches. So I put a piece of plexiglass between the board and the metal, and the backlights stayed on. I put the base on the tv so I could “stand it up” and everything was still working fine. I had it on for about four hours last night, going down to the basement about a dozen times, and turning it on and off with the switch. Worked perfect EVERY time. I turned it off, but didn't unplug it, when I went to bed last night. This morning I went down and turned it on (white logo) but no backlights. I took the piece of plexiglass out and moved the board up and down like I did yesterday but again,,,,,,,,,,,,,no backlights. Sorry!

[nomoresonys]

Re: Dead Vizio VL 420M

thanks for the details, this is a tough one. seems like a pesky short or something.

[Tayninh55]

Re: Dead Vizio VL 420M

Is there a way to get the wires to come out of plastic connectors without destroying them,,,,the 6 pin connector to be precise?

[CapLeaker]

Re: Dead Vizio VL 420M

I don't think there is a short. I think there is an intermittent open. So either a cracked solder joint, a broken trace or something along that line. Something doesn't make good connection, if you could make the TV work and quit by simply lifting or pressing on the power supply board.

[Tayninh55]

Re: Dead Vizio VL 420M

Since I could "make it work" by moving the Power Board, do you still think it's a "main board" problem or doesn't that fact make any difference? I know I'm probably asking the "impossible". Thanks

[budm]

Re: Dead Vizio VL 420M

You need to check and see which signals, mainly the PS-ON and BL-ON) are present when it works and when it does not work.
it may be bad solder joints, bad wire crimping on the terminals.

[Tayninh55]

Re: Dead Vizio VL 420M

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