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Old 11-06-2018, 10:09 AM   #1
reverendalc
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Default 2012 A1278 macbook pro 820-3115 no display

hello all;

i've been working on this mid2012 MacBook pro 13" A1278, board model 820-3115

symptoms: no lcd or backlight. external display works fine.

what i've tried: connecting another known good LCD. swapping MLB into another working chassis. SMC/NVRAM ad infinitum.

testing:
pp3v3_lcdvdd_sw shows 0V at all points
lcd_ig_pwr_en shows 0v
u9000 has 3v3 on S5 inputs
small damage to plastic at J6955, but no shorts/pins ok
SMC_LID reads 3.15V open and closed. should be <1V open and 3.42V closed?
pp3v3_s0_lcd reads 3.3V across L9008, C9010, and into #4 at LVDS connector
L9008 shows 4.9K with LVDS connected and around 10K disconnected.. schematic suggests 90ohm... i'm confused. i tested L9008 on working board and got 0.5ohm... confusion again.
microscope inspection of LVDS cable and and connector shows no issue

other *interesting* behavior: MacBook powers on immediately when MagSafe is connected. this is normal behavior when no battery is present, but battery is present. it's also normal behavior for closed-clamshell mode, which would make sense if the MacBook isn't getting 3V42 at SMC_LID, but if it's truly in CC mode, then the Tpad and KB shouldn't work... which they do. the lack of keyboard backlight led me to believe CC mode was possible, however when i put known good MLB in, it didn't show KB backlight either... but it didn't look like i was able to insert the ribbon cable into the ZIF fully with the known good, so that's still another variable.

i have moderate skill, passable equipment, and a boardview/schematic, but i don't know what to do with it all.

thanks in advance
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Last edited by reverendalc; 11-06-2018 at 10:13 AM..
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Old 11-06-2018, 10:19 AM   #2
reverendalc
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Default Re: 2012 A1278 macbook pro 820-3115 no display

here are photos of the LVDS cable end, connector, and battery status connector.

the plastic is damaged between pins 8/10, SMC_BIL_BUTTON and GND. i cannot test a short though, and the metals look fine.
Attached Images
File Type: png Screen Shot 2018-11-04 at 8.02.13 PM.png (315.4 KB, 16 views)
File Type: jpeg KNXbWLUyBXgcWaMC.standard.jpeg (38.4 KB, 15 views)
File Type: jpeg AJJDr2uZYcuKxpDk.standard.jpeg (37.3 KB, 17 views)
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Old 11-06-2018, 01:32 PM   #3
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Default Re: 2012 A1278 macbook pro 820-3115 no display

L9008 should measure close to 0 ohm on the multimeter so check resistance across it again. If it's high, replace it.
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Old 11-07-2018, 09:23 AM   #4
reverendalc
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Default Re: 2012 A1278 macbook pro 820-3115 no display

ok i'll swap L9008 tonight. why does the schematic identify 90ohm?
the known good test board agrees with your statement, but disagrees with apple.
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Old 11-07-2018, 10:47 AM   #5
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Default Re: 2012 A1278 macbook pro 820-3115 no display

Schematic says 120ohms on L9008, that's the impedence not the actual resistance you will mesure with a standard multimeter.
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Old 01-22-2019, 09:32 AM   #6
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Default Re: 2012 A1278 macbook pro 820-3115 no display

hey can someone send me a pic of the LCD connector capacitor location someone worked on this board and I'm trying to fix need the photo of the front of the lcd connector EMC 2554
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