820-00165 No Image - Fixed!

[tlough75]

This post is about an 820-00165 that came in with no backlight or image. I checked some power rails as was poking around and saw that L8304 looked a little dark. Well I did some measurements and compared with some other working boards of the same model and this inductor was measuring short. I decided to replace it because it looked dark, there are no signs of corrosion on the board what so ever. Well needless to say I have found that image and backlight have been restored. What I would like to ask is: Is there another component that could cause the coil to burn out? or would it burn out on its own? I'm just wondering since I want the fix to last. The downside to this is the LCD is dead. It is running on my "test" screen.

 

[2informaticos]

You mean L8304 was open, not short I suppose.
Bad video cable, or LCD panel can burn L8304.
After such fail, always need to check diode mode to ground on LCD connector, BEFORE applying power on the board.
Compare readings w/ and w/o LCD assembly connected and you can see if still there is a problem.

 

[tlough75]

According to SEM lab, an inductor can fail open or short. Usually open due to corrosion, short due to electrical overstress. I'm guessing since it measured 14k ohms vs the 0.2 that I measured on 5 inductors pulled from donors I would say you are correct that the LCD might have failed causing the inductor to fail. To your other point: I did check diode mode to ground as well as resistance both before removing the offending inductor and after, as well as after installing the replacement. Thank you for your insight as always.

 

[tlough75]

Seems like a 1 out of a few hundred scenario.