Vizio M470NV will not turn on

[dick_barton]

Re: Vizio M470NV will not turn on

Hello bjhunnicutt, could you also post a clear picture of the circuit board shown within the white box.
Thanks

[dick_barton]

Re: Vizio M470NV will not turn on

Looking through previous posts it looks like VLED to chassis = 145V

https://www.badcaps.net/forum/showpo...21&postcount=7

[dick_barton]

Re: Vizio M470NV will not turn on

BL_On appears to be the 3rd pin down. Sharper picture would help since it's quite blurry.
Put your 1K resistor from 5VSTB to Power_On (4th pin down) and place another 1K from +5V to BL_ON with mainboard disconnected and then measure VLED

Basically follow same advice as in post #10

[CapLeaker]

Re: Vizio M470NV will not turn on

Okay, So I was able to jumper a 5v to the power_on pin (fourth on from the top) and got 12v on all 3 of the 12v pins. When I jumpered a 5v volt to BL_on I got nothing from the backlight. Just to confirm is BL_on 2nd from the top or third? (see most recently attached picture) The first is hidden by the plastic retainer and the Power_on label takes up two pins. Also, originally the Vizio logo (stby light) would glow orange when plugged in, but no longer does. I still get the feeling I am missing something.

Thanks all

You got something wrong with the pins. PSon is only ONE pin (#4 counted from right to left) BLon is #3, no connection on #2, PWM for #1.

Force the PSU on (like in my post #10 earlier) with just the backlights hooked up... Check all the voltage rails and measure each LED string. I am not sure how much juice is on the LED string exactly but it should be around 100VDC or so.

[bjhunnicutt]

Re: Vizio M470NV will not turn on

Here are some higher resolution photos of my boards.

[bjhunnicutt]

Re: Vizio M470NV will not turn on

Daughter Board

[bjhunnicutt]

Re: Vizio M470NV will not turn on

Post 12 has a clear close up of the 5v/12v/Pwr on section of the power board

Post 18 has a clear close up of the LED connectors

Thanks

[bjhunnicutt]

Re: Vizio M470NV will not turn on

Thanks for the clarification on the pins, I will reattempt this afternoon. And post the vled voltages

[budm]

Re: Vizio M470NV will not turn on

OK, so you are able to force on the power supply board using the resistor, we need to find out if the PFC Voltage booster is working or not by check the DCV between the two legs of the main filter caps (two 450VDC caps laying on their side) to see if it has close to 400VDC or not since the LED backlights circuit requires that boosted Voltage to work.

[bjhunnicutt]

Re: Vizio M470NV will not turn on

BudM, forgive this basic question, but where do I put the tester probe to check that? (I do know which ones are the 450v caps and I see the two legs)

[budm]

Re: Vizio M470NV will not turn on

You can check either one of the two caps since they are connected in parallel, red probe on the plus leg, black probe on the negative leg.

[bjhunnicutt]

Re: Vizio M470NV will not turn on

Here are the voltages I got:
All the 5v = 5v
All the 12v = 11-12 volts
The 4 VLEDs = 105-115
The 450 Cap = 340-360

With the LED connectors plugged in. But no Backlight.

Does this mean the backlight array is dead? Or are the voltages to low? Is it common for the entire array to die?

[CapLeaker]

Re: Vizio M470NV will not turn on

The backlights are like X-Mas lights. One fails, all go out in that string. The 4 VLED's voltages are at 105 to 115 V DC but no backlight?

[bjhunnicutt]

Re: Vizio M470NV will not turn on

Correct, no backlight with the voltages stated. Also, no sound if it matters

[CapLeaker]

Re: Vizio M470NV will not turn on

weird. there must be an open somewhere on the LED strings. Are you measuring with the probes from VLED - to VLED +?

[budm]

Re: Vizio M470NV will not turn on

You have 12 strings of LEDs (1-1, 1-2, 1-3, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 4-1, 4-2, 4-3: These pins are the Cathode returns of each LED string) driven by 12 LED drivers.
VLED pins are the outputs of the boost converter circuits and connected to the Anode of all the LED strings.
So for sure if you look at the panel in the darkened room you did not see the backlights flash on for seconds? I doubt that all 12 strings of LED will be bad.

[bjhunnicutt]

Re: Vizio M470NV will not turn on

I agree it doesn't make sense which makes me think I am doing something wrong.

I checked the voltage with the hot probe on the vled pin (all four, one at a time) and the ground probe on a point on the frame.

I have done this in a dark room, no light at all from the unit.

Is there a fuse or something downstream of the vleds and prior to the led strings?

[CapLeaker]

Re: Vizio M470NV will not turn on

No. you have to measure each LED string like budm mentioned in his last post.

[bjhunnicutt]

Re: Vizio M470NV will not turn on

So probe each of the 1-1, 1-2 etc pins individually?

[bjhunnicutt]

Re: Vizio M470NV will not turn on

When I turn the power on with the PWR_ON and BL_ON jumpered the screen does flicker initially and then returns to black (or at least imperceptibly dim) I missed it before because I wasn't looking straight at the screen at power up due to the set up of my work space. What does this change?

Also, how do I measure the individual LED strings? Currently I get 110 on all the vleds (far left and far right of each plug) and 0 on the 12 (1-1....4-3) cathode returns