Vizio M470NV will not turn on

[CapLeaker]

Re: Vizio M470NV will not turn on

VLED to 1-1... VLED to 1-2 etc...

[bjhunnicutt]

Re: Vizio M470NV will not turn on

Sorry, CapLeaker but could you elaborate.

[CapLeaker]

Re: Vizio M470NV will not turn on

Put the meter to measure DC. Put one probe to the VLED pin then the other to 1-1, 1-2, 1-3, etc pin. Go through them on both connectors. Take note of the voltages measured and report back. One probe is always on the VLED pin, while the other probe goes to each numbered one (1-1 up to 1-3, then 2-1 -> 2-3, on the other connector same thing.

[bjhunnicutt]

Re: Vizio M470NV will not turn on

They will each show 105-110 volts for about 3-5 seconds after the power is turned on then go to zero. This corresponds to the screen flashing on for a few seconds when the power is turned on and then going dim.

[bjhunnicutt]

Re: Vizio M470NV will not turn on

PS- Thanks for the detailed instructions, I am learning quite a bit

[CapLeaker]

Re: Vizio M470NV will not turn on

The backlight actually does come on for a second or two... that is better and what we expected compared to nothing at all. Isn't one VLED rail that shows a big difference compared to the others? Since the PSU actually does put out, you have to disassemble the panel and see if all LED's come on.

[bjhunnicutt]

Re: Vizio M470NV will not turn on

I didn't notice a big difference between the VLED rails.

Any speculation on what causes the shutoff after a few seconds?

[budm]

Re: Vizio M470NV will not turn on

Do the same test again but this time put the black probe on the chassis and the red probe on 1-1, 1-2, and so on.

[bjhunnicutt]

Re: Vizio M470NV will not turn on

With black probe on the chassis and red probe on 1-1 etc. I get 0v on all 12, not even the temporary 105v I get when doing 1-1 etc to VLED as earlier posted. The screen still flashes for a 2 or 3 count when power is first applied. It looks to be the entire screen, no obvious gaps.

[bjhunnicutt]

Re: Vizio M470NV will not turn on

Because the thread has become a bit lengthy (I appreciate all of the assistance) I thought I would recap where I am with this TV.

While watching tv there was an audible pop and the unit died and wouldn't turn on. After a bit of trial and error I have the following voltages coming off the power supply board.

With PWR_ON and BL_ON jumpered:
5V out of all the 5V
11-12V out of all the 12V
340-360V out of the 450V caps
105-115V out of the VLEDs when tested with the hot probe on the VLED and the gnd on the chassis
105-115V out of the VLEDs for about 3 secs when tested with the hot probe on VLED and gnd on 1-1....4-3. Then drops to 0.
0V out of 1-1....4-3 with the hot probe on 1-1...4-3 and gnd probe on the chassis.

Also, when power is applied with PWR_on and BL_on jumpered, the screen does flash white for about 3 sec.

The orange VIZIO logo standby light doesn't light up when power is applied.

Thanks for all the help. I am preparing to take it apart further to look at the LED strings per post 46

[CapLeaker]

Re: Vizio M470NV will not turn on

I didn't notice a big difference between the VLED rails.

Any speculation on what causes the shutoff after a few seconds?

a bad led string (backlights), making the PSU shut down.

[bjhunnicutt]

Re: Vizio M470NV will not turn on

When I get the panel disassembled will that bad string be visually obvious (not lighting up or blackened looking etc) or will I need to do some more testing?

[budm]

Re: Vizio M470NV will not turn on

I still need to do some more thinking since all the Cathode returns (1-1,1-2,.. ) of ALL the strings with Ref to the Chassis to GND readings ALL show 0V, I cannot see that all the strings will have open circuits, unless the VLED Voltage has to be higher than 115V.
Need to find out how many LEDs there are in each string, I sure hate to open up the panel and taking a chance of damaging the LCD Glass panel.
We need to see if we can find the pictures of the LED strings on the web.

[budm]

Re: Vizio M470NV will not turn on

BTW, to make sure I get this correctly, you DO SEE the backligts do come on for seconds?

[bjhunnicutt]

Re: Vizio M470NV will not turn on

Yes the screen flashes white (a uniform flash covering the entire screen) for about 3 sec then goes black. This did correspond to the VLED to 1-1...4-3 probe test where the voltage goes from 105ish to 0 after about 3 secs. FYI, I am using an analog multimeter.

Also I won't be tinkering with it this weekend, so you will have time to think about it further.

I appreciate everybody's time and input.

[bjhunnicutt]

Re: Vizio M470NV will not turn on

I found these. It is unclear if the associate picture is a generic LED or the specific one

http://vizpartsdirect.com/productDet...temInfoId=1763

[budm]

Re: Vizio M470NV will not turn on

Ahh, analog meter! I which we know that at the beginning or may be it was mention some where in the thread.
OK, you are using the analog meter which is not going to be fast enough to catch the Voltage readings between GND and 1-1, 1-2, ... before it goes into protection mode.

[bjhunnicutt]

Re: Vizio M470NV will not turn on

I don't believe I mentioned it earlier, my mistake.

Can you explain how the protection mode works?

How does that change the diagnosis?

And should I go by a digital one?

[budm]

Re: Vizio M470NV will not turn on

If one string of the LED has open circuit the VLED will go up above the Over Voltage trip point, it also has detection for over current draw if one or more of the LEDs are shorted out.
See PDF of the typical LED driver function.

[bjhunnicutt]

Re: Vizio M470NV will not turn on

Ok, so it doesn't really change the diagnosis and I will still need to take a look at the LED strings.

Also, I found this picture and description -

http://www.vizpartsdirect.com/produc...temInfoId=1763