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The larger of Apple's MacBook Air laptops featuring dual microphones and 802.11ac Wi-Fi connectivity.

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dim backlight after liquid damage

i have a macbook air 820-3437 which was liquid damaged, doa. corrosion was around smc and u7700, reballed smc and it turned on however dim backlight. is u7700 the issue or is there anything else i can check

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@tcrs_circuit i replaced the backlight fuse as i wasnt getting the same voltage on both sides, however now it wont turn on at all, no green light on charger and no fan spin, i tried injecting voltage into pin to but it wont go past 0.05 amp on 8.5v

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Sounds like something got messed up... Please tell me you didnt do this with power plugged in

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do what test the fuse ?

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2 Answers

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I'd definitely replace u7700, no wonder it might be the cause of the dim backlight. If you have corrosion in the area maybe there's some filth stuck under it. If you don't have a replacement try at least a reheat with quite a bit of no clean flux..touch it a little to confirm solder melting point, if it's just residues it might get cleaned and kick back in properly.

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replaced u7700 today with a new ic, still the same outcome. however checked the backlight fuse and even tho people say it never blows it looks discolored and im getting 8.5v at 1 side and 0.65 at the other so hopefully the replacement fuse arrives tomorrow to see if it fixes this issue

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@tech_ni Are you sure the fuse didn't blow after driver replacement ? With such voltage in you shouldn't have any backlight at all, driver shouldn't be working. I don't second the view the fuse never blows, actually that's always first thing I check when there's no backlight.

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i checked the fuse before replacing the driver aswell

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@arbaman its not turning on now, im getting pp3v42_g3h, pp3v42g3h_sw, pp1v2_s5_smc_vddc. not getting ppbus_g3h

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I see from your other comment you've replaced the fuse, right ? If that's the case you might have something shorted after the fuse that brings down ppbus. Remove the fuse to confirm and in case ppbus gets back to normal without fuse look for the short along the backlight circuit, not so many candidates luckily..

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This could be several things that are wrong. Probably the simplest solution would be checking the make sure all connections to the backlight and keyboard have the rust or calcium build up and if there is clean it using a cleaning brush, but be careful not to damage any connections.

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yea nick, smc and u7700 had corrosion, keyboard was fine. reballed smc to get power working again. think its the backlight fuse

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