Vizio VW42L HDTV10A - no sound, picture or back light

[SimBen]

Hello everyone. I've been reading the postings and have found them very informative. My brothers Vizio VW42L HDTV10A turns on with the power button, the light changes from amber to white but the back light doesn't come on and there is no sound or video that I know of. This set reminds me what a pain it is to troubleshoot without good prints of the circuit boards and their interconnections. I found and replaced one bulging cap (MC2) on the Master Inverter. This is what else I know so far.

Measurements

Power supply
CN2-1,2,3,4,5 24.5V
CN3-1,2,3,4,5 24.5V
CN5-1 3.12V
CN5-2,3,4 11.9V
CN5-10,11,12 5.2V
CN5-9 .247V
CN5-10 .011V

Main Board
J1-1 3.12V
J1-2,3,4,5 11.9V
J1-9,10,11 5.18V
J1-13 .011V
U8-1 5V
U8-2 3.3V
U1-5,6,7,8 5.14V
U1-1,3 5V
U1-2,4 0V
R20 (OPWRSB) 0V
U2-2 2.3V
U4 no component
U33-2 3.3V
U6-2 10.28V
U5-2 4.53V

I would appreciate any help I can get.

Thanks

[tom66]

Re: Vizio VW42L HDTV10A - no sound, picture or back light

These Vizios have common problems with the U33 regulator on the main input board causing the symptoms you mention. It's a three+tab legged device. The output should be 3.3V but when failed it outputs around 2V.

[selldoor]

Re: Vizio VW42L HDTV10A - no sound, picture or back light

Welcome to the forum
Pics are not too bad pic 4 is good
1 and 3 poor - please try and retake 1.
You are clearly getting some voltages so mains fuse must be ok. Have you tested the other fuses?

Pic 1 just under the connector at the top with all white and one black wire there are two white fuses with gold ends.
Pic 2 similar sort of fuse just above the connector
Pic 3 slightly different fuse above the left hand end of the big connector at the bottom.
To test Power off (for 5 mins)- meter set on ohms 20
Touch probes on each side of fuse - post result - should be same as touching the probes together.

What make/series cap did you use for replacement?

[SimBen]

Re: Vizio VW42L HDTV10A - no sound, picture or back light

I took the pictures with my cell. I will try to locate my camera and get some better ones. The fuses are good. U33 output is 3.3V but U2's output is 2.3 Volts. I replaced the cap with one with the same values from Radio Shack. I have a Cap tester. The old cap measured around 100Ufd when it should have been 470Ufd. The new cap measurements were good.

[SimBen]

Re: Vizio VW42L HDTV10A - no sound, picture or back light

This problem seems a little different than the others posted on this model in that I have NO back light, NO picture and NO sound. I have found post with two of these symptoms but not all three.

[selldoor]

Re: Vizio VW42L HDTV10A - no sound, picture or back light

I have been looking at your voltage tests and
Voltages at U2 Pin 2 2.3v is low? should be 3.3v

Voltages at U6 Pin 2 10.28 is high? should be 1.8v

Voltages at U5 Pin 2 4.53 is high? should be 1.2v

U10 pin 2?

U3 pin 1?

U3 pin 2?
Can you test/retest all these.

Are any of the pins on the connectors labelled PSON what is the voltage on that when
it is in standby and when it is on - can you measure it as you switch on.

Can you switch off with the switch.

[tom66]

Re: Vizio VW42L HDTV10A - no sound, picture or back light

Where is the black probe of your meter attached?

[shorteddiode]

Re: Vizio VW42L HDTV10A - no sound, picture or back light

I have the same TV and had the same trouble. I had to replace two voltage regulators on the main board. I'll look in the AM an see if I can fin my notes and tell you the numbers

[SimBen]

Re: Vizio VW42L HDTV10A - no sound, picture or back light

I have verifyed the voltages and they are the values that I previously stated. In addtion U10-2 is 2.6V , U3-1 is 12V and U3-2 is 5V. PSON measures .01V when I first plug in the power cord and goes to 3.1V when I push the ON button. Once the light goes from amber to white I can't turn it back off without unplugging the AC input. The 5VSB is always at 5V. I noticed that one of the flow charts decision blocks indicates that J1-13 should be at 5V for the backlight to be ON but it’s at 0V. Is there an interlock that kills everything if the backlight is not functioning?