vizio m420nv,no backlight

[flamike]

Brother brought me nonworking vizio said it would work sometimes , I never seen it light up yet, can get periodic flash during on-off cycle,checked voltages somewhat nothing obvious,no bulging caps,can see dim image and logo turns yellow to white fairly new set any ideas?

[Glitcher]

Re: vizio m420nv,no backlight

Check all the voltage regulators on the main board.

[tom66]

Re: vizio m420nv,no backlight

Check BL ON/OFF signal from main board to power supply.

[budm]

Re: vizio m420nv,no backlight

There are at least 3 white fuses, check them also.
Check the BL_ON pin on the power supply for this LED backlights TV to see what you get.

[flamike]

Re: vizio m420nv,no backlight

Im getting 3.24 volts at bl on,shoudnt that turn them on?

[budm]

Re: vizio m420nv,no backlight

That means you the problem is more likely to be in the backlights power supply.
On that power supply board, there are voltage labels for the connector, it should also have the voltage rating for the LED power supply. Can you tell us what it said?

[flamike]

Re: vizio m420nv,no backlight

on my power board it has the two plugs with letters,vled nc fb7 fb8 fb9 nc nc nc fb10 fb11 fb12 nc vled, duplicate on other side no ledger for voltages

[budm]

Re: vizio m420nv,no backlight

Try to locate the VLED voltage spec, they usually have it printed some where on the board.
Also what are the other labels on the board. Check the DC voltages on those brown caps.
It may have shorted out LED wiring also. Do you see the backlights even flash for seconds?

[flamike]

Re: vizio m420nv,no backlight

not seeing any voltage label,and yes the backlight flash sometimes on shutdown,checking caps

[flamike]

Re: vizio m420nv,no backlight



no volts on brown caps,label pics

[flamike]

Re: vizio m420nv,no backlight

thanks for all the help,Im figuring that if I get power supply everything be ok,thxs again

[flamike]

Re: vizio m420nv,no backlight

no joy,either got bad power supply or it wasnt the problem to start with

[manstoblame]

Re: vizio m420nv,no backlight

Dude I don't know much but I had been given a Westinghouse 32 inch lcd tv that wouldn't power on only had the power indicator light change from red to blue. Had only 3.5 volts when checking all voltages at the 12 the 24 or 5 I checked the voltage regulator mosfets on the power supply (the ones attached to heat sinks) DMM checked on ohms setting with the - probe attached to the center leg of device and + probe to leg on the right when the mosfets facing you. You should get a high reading that starts slowly dropping on your meter. I find that if your meter reading starts low or just reads low its bad. I replaced by ordering parts online and all my voltages appeared and tv works not saying this is your fix but checking those things can help. Just be careful checking voltages make sure you put either a clip on probe in your negative DMM slot and clip it on to the grounded screws that hold the power board down or some where on the light cabinet BE CAREFUL!!! don't get dead!!! Replace any or all Caps, and consider the possibility that the LED's could've burned out causing an automatic shut down protection? Not sure about how LED tv works hope this helps still got some kinks to work out on this set though but figured I would pass on my experience Oh because my set wont power on unless I first plug it in and as soon as power indicator stops flashing I power it on works perfect but can't turn it off and back on unless unplugged first in my case must be a power draw somewhere anyway again hope some of this helps *get service diagrams helps greatly for where to check for specific models good luck!!!