I had my Vizio VO42L fixed last year because the power wasn't working. No backlight... it wont turn on at all. This time it turn and has sound but no picture. What part(s) do i need to replace?

Sounds like it might be a solder joint. use the meter and check the ohms on each side of the solder joints on the board where the serial cables connect to the boards. it would be a good idea to check as many joints as you have time to. If it is a LED TV check Led control board for bad joints. if it uses Flourocarbon tubes check the transisters on each lighting control board. you may only have one board working causing partial back lighting.

is there any sound? Did you order the exact main board part # as your original board?

May or may not be worth fixing depending age and cost of set when new--if backlights on could be power supply (NEED TO CHECK all voltages out of power board) or even a main board etc---

Hi ,
Power on the unit in the dark room then aim a bright flashlight directly to the screen, you will barely see the images. This is because your backlight is not functioning. The following reason is the caused.
1. Power supply - missing B+(supply voltage) coming from this board feeding the inverter board. This is caused by faulty transistor, dried/leaky electrolytic capacitor, open fusible resistor.
2. Inverter board - even the B+ is good from the power supply, if the fuse, driver transistor, driver transformer is faulty no output to the backlight resulting to black picture.
3. Busted backlight - even inverter board is good but if this is busted resulting to black picture also.
Diagnosing the fault is technical and if you don't have necessary tools and test instrument and can't fix it yourself, I would advice you to look for an experienced technician to isolate the problem.
Hope I helped you.
Have a nice day!
Thanks for using Fixya.

i have the same tv same problem and its a backlight inverter. i am trying to get the back off myself to replace, as we speak

inverter board is probably bad. use a flash light to shine on the screen...if you can see a faint picture then the backlight board is bad.

No,try unplug,replug an hour later that ur reset.If same thing, ur video backlight board it dead.need it replaced.

If there is no backlight (check it in a dark room - if there's a backlight the display will be emitting light, albiet still all dark) then you're looking to replace backlight inverter (or two of them, if it's master/slave) OR the power board. To know which of the two, measure the voltage on the cable that comes from the power supply to the LCD backlight inverter board - it has lots of cables but most of them are split in 2 groups - ground and positive usually 24V. It's fairly easy to see which are which, especially on the power board.
So if there's 24V there then it's the inverter(s) and if there's nothing then it's likely the power board; it's a little tricky, though, because the main board may turn off the backlight power - so make sure you check the voltage when turning the TV on from off and watching the read.

If there *is* backlight then you;re looking at replacing the tcon board or, less likely, the main board or, least likely, the cable between them.

Please rate my response if it helps.

It's likely not a backlight, but a mainboard. If you are feeling frisky, take the back off and get the model number off the mainboard and check eBay.