VW46L FHDTV20A - backlight no image or sound

[xxNoxiouSxx]

I am new member, first time posting.

My sons VW46L went out, I have the typical no image on screen with flashlight test etc. The backlights are working as I see the white light through the holes on the back of the tv when the power is on and vizio logo goes white.

I have been reading this thread

https://www.badcaps.net/forum/showth...ighlight=VW46L

I have followed it all the way to testing F1 and F2 on the mainboard and believe that not to be my issue in this case as those fuses test continuity ok.

• F1 is 4.97v and F2 is 12.22v when unit is powered on

with the unit powered on I can confirm I am not receiving 12v at the F1 fuse on the T-con board circled in green on the T-con photo.

I have tested continuity to FB11 circled in green on the mainboard picture and this hopeful eliminates the cable as the culprit.

I have unfortunately gone as far as my level of expertise can allow me. I am comfortable testing any items that need verification via a DMM and I am hoping someone with more experience would be able to assist me in a deeper diagnoses to accomplish the following.

• confirm the main board is the problem and possibly identify the faulty part

Thank you in advance for any help you may be able to provide.

[budm]

Re: VW46L FHDTV20A - backlight no image or sound

Since you are not getting the 12V at the fuse of the T-CON then the main board is the problem for not sending out that switched Voltage to run the T-CON. How about the Voltages of all the regulator ICs on the main board, did you verify them all to be OK?

[xxNoxiouSxx]

Re: VW46L FHDTV20A - backlight no image or sound

please disregard, I see the tut in your sig. reading up on it now

[xxNoxiouSxx]

Re: VW46L FHDTV20A - backlight no image or sound

Since you are not getting the 12V at the fuse of the T-CON then the main board is the problem for not sending out that switched Voltage to run the T-CON. How about the Voltages of all the regulator ICs on the main board, did you verify them all to be OK?

I just tested the two main big ones U11 and U9

there are some others that are much smaller u2, u4, u7 and u8 those are IC's too correct? again I apologize for my ignorance here as I still have a lot to learn.

these 2 were tested with the unit powered up

U11
7805CT
RPH809 G
pin 1 = 12.22v
pin 2 = 000.2 mv
pin 3 = 5.03v

U9
1084
0845CL
pin 1 = 1.252v
pin 2 = 2.5v
pin 3 = 4.89v

[xxNoxiouSxx]

Re: VW46L FHDTV20A - backlight no image or sound

here are the following. hopefully i got them all, don't know if I missed any.

U2
AMC1117
F0826J
pin 1 = 2.069v
pin 2 = 3.328v
pin 3 = 4.89v

U4
AMC1117
F0826J
pin 1 = 2.063v
pin 2 = 3.317v
pin 3 = 4.97v

U7
AMC1117
F0826J
pin 1 = 2.065v
pin 2 = 3.320v
pin 3 = 4.90v

U8
AMC1117
F0826J
pin 1 = 000.6mv
pin 2 = 1.258v
pin 3 = 2.5v

[budm]

Re: VW46L FHDTV20A - backlight no image or sound

They look OK.
So more in-depth traoubleshooting and tracing is required.
The next step is to trace out the connections close to the LVDS connector on the main board to locate the switched MOSFET to see if it is getting the 12V input to the MOSFET or not and if it is getting the control Voltage to turn on the MOSFET or not.

[xxNoxiouSxx]

Re: VW46L FHDTV20A - backlight no image or sound

They look OK.
So more in-depth traoubleshooting and tracing is required.
The next step is to trace out the connections close to the LVDS connector on the main board to locate the switched MOSFET to see if it is getting the 12V input to the MOSFET or not and if it is getting the control Voltage to turn on the MOSFET or not.

so I am assuming that is U21?

U21
4953GM
840014
pin 1 = 12.22v
pin 2 = 11.80v
pin 3 = 12.22v
pin 4 = 11.80v
pin 5 = 004.2mv
pin 6 = 004.2mv
pin 7 = 004.2mv
pin 8 = 004.2mv

[budm]

Re: VW46L FHDTV20A - backlight no image or sound

You need to get the spec sheet of that U21 to find out what it is and its pin out. If it is the one we think it is used for supplying the 12V to the T-CON board fuse then one of the leg of U21 should show low resistance to the fuse's leg.

[xxNoxiouSxx]

Re: VW46L FHDTV20A - backlight no image or sound

You need to get the spec sheet of that U21 to find out what it is and its pin out. If it is the one we think it is used for supplying the 12V to the T-CON board fuse then one of the leg of U21 should show low resistance to the fuse's leg.

this unfortunately is where I start to go beyond my comfort zone with components. All this stuff in the data sheet is Greek to me. (attached what I believe to be the data sheet)

When I test for continuity from the T-com fuse all 4 pins (both D1 and D2 pins) on this mosfet 5-8 beep. the pins that have 004.2mv.

I am confident enough in my soldering ability to swap this component out if its the culprit. But I don't know enough about datasheets and MOSFETS to know.

even your last statement is a little above my head. I measured the resistance from the t-com fuse to each of these 4 pins and all 4 start at about 000.8 ohms fluctuate and eventually all settled around 000.3 ohms

[xxNoxiouSxx]

Re: VW46L FHDTV20A - backlight no image or sound

I jumpered that mosfet and now getting 12v power to the t-con and a beautiful no signal message on screen and a menu!

Thank you for your help!

I am going to order a replacement. seems a bad mosfet at U21 is my issue.

[budm]

Re: VW46L FHDTV20A - backlight no image or sound

Check the DC Voltage with ref. to the chassis GND and Pin 2 (Gate1), chassis GND and Pin 4 (Gate 2) so we can see if the MOSFET's are being turned on or not.

[xxNoxiouSxx]

Re: VW46L FHDTV20A - backlight no image or sound

Check the DC Voltage with ref. to the chassis GND and Pin 2 (Gate1), chassis GND and Pin 4 (Gate 2) so we can see if the MOSFET's are being turned on or not.

These were the values on the mosfet pins using chassis GND. Pins 2 and 4 were 11.80V

U21
4953GM
840014
pin 1 = 12.22v
pin 2 = 11.80v
pin 3 = 12.22v
pin 4 = 11.80v
pin 5 = 004.2mv
pin 6 = 004.2mv
pin 7 = 004.2mv
pin 8 = 004.2mv

[budm]

Re: VW46L FHDTV20A - backlight no image or sound

OK, it is not the U21 problem, it is not being turned on, the GATE Voltage has to be about 3V less than Source pins (pin 1, 3) Voltage for it to be on.
So if you connect a 470~1000 Ohms resistors between Pin 1 and GND, pin 3 and GDN it should then turn on the U21.

[xxNoxiouSxx]

Re: VW46L FHDTV20A - backlight no image or sound

OK, it is not the U21 problem, it is not being turned on, the GATE Voltage has to be about 3V less than Source pins (pin 1, 3) Voltage for it to be on.
So if you connect a 470~1000 Ohms resistors between Pin 1 and GND, pin 3 and GDN it should then turn on the U21.

I had to use pins 2 and 4 to ground as they are the gates; thank you so much for your help! this work perfectly and restored my sons tv to working order.

Nox

[budm]

Re: VW46L FHDTV20A - backlight no image or sound

'So if you connect a 470~1000 Ohms resistors between Pin 1 and GND, pin 3 and GDN it should then turn on the U21.' They are typo, it should be GATE pin 2, and pin 4.
So it means the micro controller on the main board is not sending the ON command to turn on the MOSFET. You can leave the resistors in place for now and use it until the main board dies.