duff screen detection.

Just possible if you have a source of polarized light and/or polarized glasses. Any defects in the screen *MIGHT* show up as irregularities when viewed with polarized light or through polarized glasses. Back in the day, I used a helium-gas (polarized) light source and a super-flat lens to detect defects in flat surfaces.

Just a thought.

Peter Wieck Melrose Park, PA

Depends. Some TVs with back lighting failures shut down, but others continue to run. If you have sound (check every input), the TV is not shutting down and a *bright* flashlight shown on the screen at several angles may show a dim picture. If you can get that far, look for a screen with no cracks and no lines or bands in the image. Look OK?, pull the screen.

If the TV doesn't shut down and has more than one "channel" of LED lighting, *disconnect* the LED harness and use an LED tester to light up any remaining working part of the LED array. With the LEDs partially running, turn on the TV and observe the pic. It will be dim and uneven, but you can access the overall condition of the display.

If it shuts down, go over the screen with that *bright* light and look for cracks. There are ways of fooling the TV into not shutting down with a back light error but it's usually easier to just use a bright light.

I've done several thousand at least back lighting repairs, and sometimes I discover a crack only when the screen is removed. I hold the screens up to my shop lights as if I was making an offering to the TV gods. A crack will be visible when holding it up to a bright light from behind.

Sometimes, you can repair the back lighting and you might discover an electrical failure of the display or a debonding of the ribbons either at the address boards or at the glass itself once you put it back together. Nothing you can do about that - it happens.

That all said, I can tell you that pulling screens on TVs is delicate and most amateurs break nearly all the screens they attempt to fix (no offense). Many screens are taped in the frame and must be heated carefully and a thin membrane used to separate the screen from the frame. They crack so easily you won't even know it until you put it together. If the screen isn't sitting back down flush in the frame when the mask is reinstalled you will crack the screen. If the address boards are not handled like newborn chicks, you will damage one or more of the ribbon bonds to the screen.

I normally disconnect the screen by lifting off the back assy - just leaving the display layers flat. No thought of moving it around, unsupported. That's asking for trouble.

Having tested and found dead leds or led strips, it was dissapointing to see obvious impact damage on the semiconductor screen layer, after the backlight was repaired.

No outward sign of mech trauma.

Leds were only $7.50, but took a month to swim here. I assume screen layer replacements don't make sense $-wise.

RL