VIZIO VA26LHDTV10T has white vizio logo before pressing power on. no backlight.

[triplefour]

i picked up this VIZIO VA26LHDTV10T today from the recycling center for 10$ as soon as i plug it in, the vizio logo turns white. i think its supposed to be amber first, in standby until i press power but it just turns on as white, i never see the amber. pressing the power button does nothing. it doesnt turn it off or on. its just "on" immediately as soon as i plug in the power.
the backlight does not come on, its just a blank unlit screen.
i took it apart and tested some voltages which i will post.
i dont see any bad caps or any fried components.

i thought that ceramic capacitors are non polarized, so why am i getting a zero voltage reading on one side like its a ground? or is that a sign that the capacitor has failed?

i took all these measurements with the negative lead of the main filter cap as the ground. except the connector measurements which i used chassis screw as ground.

i can see clearly im not getting the right voltages to the mainboard. if the white light is on it should mean the 12v power is flowing but it isnt..im only getting .09
so what may be going on here?

[triplefour]

Re: VIZIO VA26LHDTV10T has white vizio logo before pressing power on. no backlight.

the "primary" and "secondary" markings on this board are pretty ambiguous...

[triplefour]

Re: VIZIO VA26LHDTV10T has white vizio logo before pressing power on. no backlight.

getting some weird measurements on IC902 which is labeled A6069H SK981

for one thing the 6th pin seems to be missing.

and pins 7 and 8 make my voltmeter make some crazy feedback noise and the current alternates between 12v and 1 and then eventually just stays at 1.. or something like that. its weird.

could it be this chip is bad?

[philliesfan30m]

Re: VIZIO VA26LHDTV10T has white vizio logo before pressing power on. no backlight.

vizio's are known for having bad voltage regulators on the mainboard. i would check u150-u154 and see what voltage readings you are getting my guess is probably 1 of them is bad. some might be fixed or adjustable. you will have to check the numbers on the regulators to find out what they are. i can't tell from the pics. i don't think that chip is bad or you probably wouldn't have any standby voltage.

[triplefour]

Re: VIZIO VA26LHDTV10T has white vizio logo before pressing power on. no backlight.

ok yeah that logic makes sense.
its seeming more like a mainboard issue.
i guess i could jump the power board to really test that...
so on the voltage regulators all look fine to me but maybe im wrong so heres the measurements i got:
u150
L302
1: 0
2: 3.3
3: 5

U151
L1117-33
1: 0
2: 3.3
3: 5

U152
L302
1: 0
2: 3.3
3: 5

U153
L1117
1: 1.25
2: 2.5
3: 4.2

U154
L1117
1: 0
2: 1.25
3: 2.5

[Dgtech]

Re: VIZIO VA26LHDTV10T has white vizio logo before pressing power on. no backlight.

Did you already check the capacitor's with a meter?

[Ltank]

Re: VIZIO VA26LHDTV10T has white vizio logo before pressing power on. no backlight.

Is 498 resistor open looks like a burn spot next to jumper. These very low ohm resistors are wire wound either show short when good or open when bad. Its a 47 mili-ohm value 2 Watt
Resistor

[budm]

Re: VIZIO VA26LHDTV10T has white vizio logo before pressing power on. no backlight.

getting some weird measurements on IC902 which is labeled A6069H SK981

for one thing the 6th pin seems to be missing.

and pins 7 and 8 make my voltmeter make some crazy feedback noise and the current alternates between 12v and 1 and then eventually just stays at 1.. or something like that. its weird.

could it be this chip is bad?

This section is the standby power supply, it is working otherwise you will not have WHITE VIZIO LOGO. I hope you did not damage the meter, that pin 7-8 are the Drain pin which will have high voltage spike on them.

[budm]

Re: VIZIO VA26LHDTV10T has white vizio logo before pressing power on. no backlight.

BTW, right now PS_ON is less than a Volt but enough to turn on the PFC Voltage booster to give you 370VDC on the two legs of the MAIN filter cap, no ON/OFF signal to turn on the backlights, no 12V, 24V either. I hope that voltage readings you are showing in the primary side are done using the correct Ground ref point. What did you use for Ground ref point?

[budm]

Re: VIZIO VA26LHDTV10T has white vizio logo before pressing power on. no backlight.

the "primary" and "secondary" markings on this board are pretty ambiguous...

You can see thick black line for the separation between Primary and the Secondary.

[budm]

Re: VIZIO VA26LHDTV10T has white vizio logo before pressing power on. no backlight.

Power supply board block diagram.

[triplefour]

Re: VIZIO VA26LHDTV10T has white vizio logo before pressing power on. no backlight.

yes i used the negative leg of the main filter cap as the ground reference for all those measurements except the ones on the connectors. i used the chassis screw for those. thanks for the block diagram, that is very educational.
i dont think i damaged my meter...it still reads everything else correctly....
my meter can measure up to 600v so it would have to be really high voltage to break that, right? sure dont want to break my meter!
i havent checked any of the capacitors, because i would need to desolder them to do so, (and they all look fine) and id rather poke around a bit more before i just start guessing... is there some way i can test a capacitor (even a really crude test just to see if its totally broken) before taking it out? ill check resistor 498 for open and post back in a minute.

[triplefour]

Re: VIZIO VA26LHDTV10T has white vizio logo before pressing power on. no backlight.

ok resister R498 read at .8 ohms so thats not it...

[triplefour]

Re: VIZIO VA26LHDTV10T has white vizio logo before pressing power on. no backlight.

guess i may as well test all the other resistors for open...

[triplefour]

Re: VIZIO VA26LHDTV10T has white vizio logo before pressing power on. no backlight.

wait it was R948 not R498... either way i tested all resistors and diodes i could see and none of them were open. all had some resistance.

[triplefour]

Re: VIZIO VA26LHDTV10T has white vizio logo before pressing power on. no backlight.

i noticed that diode D935 allows current to pass in both directions. that cant be right, can it?

[budm]

Re: VIZIO VA26LHDTV10T has white vizio logo before pressing power on. no backlight.

As I indicated in post 8, again, that section of the standby power supply is working otherwise you will not get the white VIZIO Logo. You have problem with the 12V24v POWER SUPPLY SECTION, not in the section as shown in post 3.

[triplefour]

Re: VIZIO VA26LHDTV10T has white vizio logo before pressing power on. no backlight.

ok but a diode that can pass current both ways is defying the normal concept of what a diode is, isnt it?

[triplefour]

Re: VIZIO VA26LHDTV10T has white vizio logo before pressing power on. no backlight.

i guess it doesnt matter since as you say thats in the 5v standby section and i do have that. what im wondering then is why the logo is white, when it should be amber. also what can i test in the 12v24v section?

[triplefour]

Re: VIZIO VA26LHDTV10T has white vizio logo before pressing power on. no backlight.

i really would like to know an explanation for how a diode can pass both ways though...kinda messing with me