Vizio VW26LHDTV10F, No Sound, Backlight and Standby Light

[Grannyrogers]

No sound, No backlight, No standby light..

When the power button is pressed, nothing happens.

Tests that I have done:

Power Supply:

Legs of large capacitor registers 402v consistently

With logic and inverter board unplugged, I registered 5v only on connector pins labeled "5v"

With logic and Inverter plugged in, I registered 24.5v to the inverter and 14.45v and 5v to the logic board.

Logic Board

regulators:

u3
AC 7A1L
17-33L
PIN1=0
PIN2=.78
PIN3=1.68

U5
AC 7A1L
17-33L
PIN1=0
PIN2=.82
PIN3=1.69

U6
AZ1084S
-ADJE1
713J71
PIN1=.50
PIN2=.81
PIN3=1.69

U8
A1084S
-ADJE1
713J71
PIN1=.42
PIN2=.80
PIN3=1.69

U9
AC 713L
1117L
PIN1=0
PIN2=.09
PIN3=.81

U10
AC 7A1L
17-33L
PIN1=0
PIN2=3.30
PIN3=5.03

U11
AC713L
1117L
PIN1=.01
PIN2=.04
PIN3=.81

U28
J201
78M12
PIN1=14.45
PIN2=.01
PIN3=11.93

U31
UTC
78D05AL
05UKCG
PIN1=11.93
PIN2=.01
PIN3=4.99

U33
AC 7A1L
17-33L
PIN1=0
PIN2=.72
PIN3=1.69

Any Help is appreciated. Thanks

[Grannyrogers]

Re: Vizio VW26LHDTV10F, No Sound, Backlight and Standby Light

Here are some Pictures:

[budm]

Re: Vizio VW26LHDTV10F, No Sound, Backlight and Standby Light

You need to retest the input voltage to pin 3 of U3, U5, U6, U8, U9, U11, U33: they are way too low.

[Grannyrogers]

Re: Vizio VW26LHDTV10F, No Sound, Backlight and Standby Light

Thanks for replying so quick Budm.

I rechecked all of them with the MM black wire to chassis, and I am still getting the same values.

I forgot to mention that I replaced two bulging capacitors on the powersupply. they were 2200 uf 10v each.

Do you think the main board is no good?

[budm]

Re: Vizio VW26LHDTV10F, No Sound, Backlight and Standby Light

The problem is on the main board right now due to very low DC input voltages feeding those regulators, need to find out why you are getting only 1.69V,and 0.81V to those input pins.
One things that does not make sense is that you are able to get the 24V isnce with that low voltages on the main board, it will not function to send out the PS_ON signal to turn on the 24V power supply.

[Grannyrogers]

Re: Vizio VW26LHDTV10F, No Sound, Backlight and Standby Light

Is there anything else I can test?

[Grannyrogers]

Re: Vizio VW26LHDTV10F, No Sound, Backlight and Standby Light

The problem is on the main board right now due to very low DC input voltages feeding those regulators, need to find out why you are getting only 1.69V,and 0.81V to those input pins.
One things that does not make sense is that you are able to get the 24V isnce with that low voltages on the main board, it will not function to send out the PS_ON signal to turn on the 24V power supply.

I did some reading, and it seems the 24v is active because the PS-ON signal coming from the mainboard is low. Normally, when the TV on/off swtch is pressed, the voltage to the PS_ON drops which tells the power supplies to initiate the 24v

[budm]

Re: Vizio VW26LHDTV10F, No Sound, Backlight and Standby Light

Hmm, most Vizio uses active high, but may be this one is active low. What is voltage at PS_ON when TV is in standby mode? The main key right now is to find out why we are having really low voltage feeding the regulator ICs. You may have trace out to see if all those input pins are tied together on the one with 1.69VDC reading, then trace out where it goes after that.

[Grannyrogers]

Re: Vizio VW26LHDTV10F, No Sound, Backlight and Standby Light

I cant tell if TV is in standby mode or not because the standby light is off. However, the voltage at PS_ON is 1.205v.

[budm]

Re: Vizio VW26LHDTV10F, No Sound, Backlight and Standby Light

It should toggle when the power switch is turned on and off, if it does not change state, then that control line is also not working.

[Grannyrogers]

Re: Vizio VW26LHDTV10F, No Sound, Backlight and Standby Light

Nothing happens when I toggle the on and off switch. The voltage does not fluctuate, so that control line appears to be dead as you stated. Mystery deepens.

I get .02v at on/off and .80 at IVT_DIM

[budm]

Re: Vizio VW26LHDTV10F, No Sound, Backlight and Standby Light

Nothing is going to work right until we get the correct voltages from those regulators.

[Grannyrogers]

Re: Vizio VW26LHDTV10F, No Sound, Backlight and Standby Light

I tested this 8 legged thing and it has the correct 5 volts on one side and the 1.69v that we see going to the regulators on the other side. Oh and that 1.69v is now 1.65v. It is decreasing. I am going to upload a pic of it. I think it is called variable capitance diode.

Could this be problem?

[Grannyrogers]

Re: Vizio VW26LHDTV10F, No Sound, Backlight and Standby Light

Hey budm,

So I ordered a mainboard off ebay for $38 and I just installed it; however, when I press the power button all I got was the standby light and backlight. I tested the voltages and I got normal voltages. 5.03v, 15.06v and 24v. However, shortly after, I smelt something burning and when I tried turning tv off, nothing would happen. I unpplugged the tv then replugged it back into the outlet and now it is as before, just a black screen with no standby light. I retested the voltages and they are, once again, just as on the old board. All low voltages going to several regulators except one. Do you think a bad Tcon board could cause this or is it a bad power supply?

[Grannyrogers]

Re: Vizio VW26LHDTV10F, No Sound, Backlight and Standby Light

Oh. On the new board, an 8 prong mosfet is burnt. It is located beside the connector from the PS. The volts coming from it matches the volts going to the regulators.

[tom66]

Re: Vizio VW26LHDTV10F, No Sound, Backlight and Standby Light

Can we see a picture of this burnt MOSFET? The seller probably didn't test the board, they rarely do.

[Grannyrogers]

Re: Vizio VW26LHDTV10F, No Sound, Backlight and Standby Light

Can we see a picture of this burnt MOSFET? The seller probably didn't test the board, they rarely do.

Hi tomm66, thanks for assisting.

The board I bought was good when I got it. The original one had no standby light, no sound, no backlight, but when I installed the new one, I saw standby light and I got a white backlight then I smelt something burning.

Upon closer inspection of the original board i notice that the same MOSFET was burnt as well. I have uploaded pictures of both.

What do you think is causing the mosfet to burn up?

[budm]

Re: Vizio VW26LHDTV10F, No Sound, Backlight and Standby Light

It looks like it is being used as a switch.