Vizio VX37L backlight not coming on

[aaronwt6]

Picked this one up today for $25 and came home and took the back right off. Vizio light turns from Amber to White when I power it up with the remote or button the side. Started by testing the standby and as expected, its putting out 5V. When I power it up, the PSON shows 5V as well so I figure the control board is working. Moving on to the 24V outputs, they start out at 14V and quickly drop to 1-2V. I've pretty much decided it needs some work on the supply but thought I'd post for knowledge and reference in case someone else needs it. Opinions welcomed on where I could start with testing the supply for repair or if there could be another problem causing this.

Thanks as always,

Aaron

PS, seems that these broken Vizio TVs are a dime a dozen. Bad trend.

[aaronwt6]

Re: Vizio VX37L backlight not coming on

Well, I found this thread so I'm doing some reading now.

https://www.badcaps.net/forum/showth...ht=vizio+vx37l

[johnboy1313]

Re: Vizio VX37L backlight not coming on

Check U7 and U33 on the main board per this thread.

https://www.badcaps.net/forum/showth...tage+regulator

[aaronwt6]

Re: Vizio VX37L backlight not coming on

Will do. I got put on kid patrol but I'll start there next.

[budm]

Re: Vizio VX37L backlight not coming on

I would check all the regulators just to be sure, but the common failure ones are the U7 and U33 as indicated by Johnboy.
Does the PS_ON drop out when the 24V drops down? How about the BL_ON (it is one of the A, or B pin)?

[aaronwt6]

Re: Vizio VX37L backlight not coming on

Haven't had a chance to look at U7 and U33. PSON holds steady at 4.98V when I hit the power button. 5VSBY holds steady at 5.03V all the time. All three pins labeled 'B' show 0V all the time. All three pins labeled 'A' show 0.2V with the power off and 2.96V with it on. I'm assuming that 3V must be the BL-ON trigger but I guess maybe it should also be around 5V.

Oh, and there is absolutely no reading at all on the 12V pins regardless of power state. I can also unplug the control wires completely and jump from 5V STDBY to PSON and get the same effect. 14V on the 24V pins that quickly drops to around 1-2V and stays there.

Probably have to check U7 and U33 tomorrow due to time constraint but it seems I have the same effect without the control board.

[Pentium4]

Re: Vizio VX37L backlight not coming on

Doesn't hurt to test that inverter transformer too (T1)

[budm]

Re: Vizio VX37L backlight not coming on

OK, so it looks like we need to work on the power supply first to get the 12v/24v working first.
So lets see if the PFC Voltage booster circle is working or not fist, when TV is plugged in but not turn you should have about 160~170VDC on that main 450VDC filter cap, then it should go up to about 380~390V when PS_ON is present.
Be careful since you will be working in the hot side of the circuits so do not touch anything with your hands, measure the voltage directly at the two legs of the cap, make sure not to slip the probes!

[aaronwt6]

Re: Vizio VX37L backlight not coming on

Thanks budm. I'll check this out as soon as I get home from work this evening and report back. Would certainly be nice to repair the power supply instead of replace.

[aaronwt6]

Re: Vizio VX37L backlight not coming on

U7

0V
1.82V
3.02V

U33 appears to be an IC

Main cap I have 172.2V with tv in standby and 407V with it on.

[tom66]

Re: Vizio VX37L backlight not coming on

Are there not more regulators than U7?

[aaronwt6]

Re: Vizio VX37L backlight not coming on

Tons.

U5, U10, and U9 all have those same readings

U8, U4, and U6

0V
3.33V
5.11V

I'm looking at others now

U16

0V
2.52V
5.01V

DU2

0V
3.3V
5.01V

[tom66]

Re: Vizio VX37L backlight not coming on

U8, U4, U6 and U16 are suspect. What are the part #s on them?

[aaronwt6]

Re: Vizio VX37L backlight not coming on

Now this seems strange. DU1 in the upper left of the board that seems like a higher current regulator has only 0.544V in and nothing out.

[aaronwt6]

Re: Vizio VX37L backlight not coming on

I rechecked readings on those. Wrote them down wrong. See above

U8 and U4

Part number
6I2L
17-33L

U16
Part Number
6H3L
17-25L

[aaronwt6]

Re: Vizio VX37L backlight not coming on

Think Ive checked every one I see

[tom66]

Re: Vizio VX37L backlight not coming on

Can you verify your multimeter reading by testing a fresh 1.5V AA battery?

[aaronwt6]

Re: Vizio VX37L backlight not coming on

Yes sir. 1.51V on an AAA

Was still leaning toward the power supply on this one with the lack of 12V and the fact that the 24V drops out. Sounds like you are taking a different direction?

[tom66]

Re: Vizio VX37L backlight not coming on

Well multiple regulators are all reading low which is really strange.
So I'm going to suggest you replace all of U4, U6 and U8... Did you update U16 I swear it said 2.22V before?

[aaronwt6]

Re: Vizio VX37L backlight not coming on

U16 is 2.52V. You think the supply could cause all that?