I have dark horizontal band across the top of my Vizio M4470NV how can I check the back light led's

SOURCE: dark/light horizontal bands...

I've examined this same problem, and found it's due to worn out electrolyte condensers (the little metal cylinder you can see on the main board). Maybe few of them are at fault, but since the problem is connencted to aging of components, it's convenient to replace them all. Servicing is not simple, because you need identical replacement parts, suitable tools and a certain skill. Best luck.

SOURCE: Toshiba 52WM48 - Dark line across top of screen about 4 inches

replace the vertical ic, LA 7833 and four capacitors near it, i encountered this last two days.change the parts and it ok now.
cost of this parts is about $20.00

SOURCE: Dark horizontal band at top of Sony KDF - 46E 2000 TV

rca ps2720lv blue is very dim any suggestions

SOURCE: Vizio VW46L10 TV has a 6 inch dark band across the top of the picture.

Change input device to some other like a DVD player.
Switch off TV, switch off power, remove plug and wait for 48 hours and retry. If problem persists, call in a qualified service technician.

SOURCE: Vizio E480i-b2 LED TV loosing picture and sometimes shutting off

I don't think you had backlight issues like you thought you did as the set should have shut down the backlights totally as soon as it sensed over voltage or over current, I'd try a new main board and see if that fixes things up for you