Chosen Solution
I replaced the LCD for a customer and a couple of weeks later he reported the left side of the display to be dim. Note that the battery was unplugged during the repair and there were no signs of liquid or physical damage inside of the phone nor on the LCD prior to the initial repair or when he brought it back in. I replaced that screen under warranty assuming that it was a defective LCD. The newest replacement LCD worked fine at first. But, a couple of hours later he reported the BL went out on the right side of the second LCD replacement. I’m pretty sure I didn’t have two defective LCD’s both with BL issues. I tested the first replacement LCD on a tester phone and the BL was still out on it. It seems then that in both cases, I put a good LCD on the phone and that the phone somehow eventually damaged the backlights on each LCD. I’ve not experienced this particular issue before. Has anyone? I have only seen BL circuit blown out from people not unplugging the battery during a repair in which case you see the backlight issue as soon as you connect a new screen. Or when the solder joints make contact with the back shield. Neither was the case in this situation.
There are two possible scenarios that I can see: You possibly have a bad batch of LCD’s. You’ll want to look at this carefully in terms of batch/vendor etc.If this is a logic board issue, then I would look at the backlight filter. This is a Ferrite Bead and the purpose of using a FB is not to act as a fuse but to filter out high frequency noise. A FB will let DC pass but filter out high frequency noise. When there is too much noise on the line it becomes resistive (whatever the spec says, i.e. 33R). Perhaps this phone has been repaired in the past and someone just jumpered the filter instead of replacing it meaning that high frequency noise is getting to the actual backlight.Otherwise, if the screens are good then you may want to wipe the entire BL circuit and rebuild.
