[solved]820-3209-A no backlight

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maazkamani

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i have a 820-3209 macbook air logic board. liquid damaged... no backlight. did ultrasonic cleaning and measured fuse. fuse is ok. damage was main on LED driver. i was wondering what would be the diagnostic steps to know where the issue might be .

thanks in advance
 
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maazkamani

New member
bkl_en measured on r9715 2.7v

bkl_pwm on r9704 - 3v

from a5 probe to c9796 there is continuity
 
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aprendiz

Moderator
Do you have PPBUS_SW_LCDBKLT_PWR? If no Check LCD_BKLT_EN and BKLT_PLT_RST_L......
 
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aprendiz

Moderator
ok missing LCD_BKLT_EN = LVDS_IG_BKL_ON this signal cames from PCH, measure on diode mode red probe to ground pin 5 from Q9707, this could be a bad PCH....
 

aprendiz

Moderator
diode mode red probe to ground black probe to pin 5 from Q9707 should give you a value about 0.400 or something like that..... are you sure it is just 1 ??
 

maazkamani

New member
r9741 is showing 5 ohms. i was wondering if that has relation to the no backlight or does that relate to something else

also i saw some corrosion on q9707... very minor but now pin 5 is getting 3.3v
PPBUS_SW_LCDBKLT_PWR=8.36v now. dont know what happen but these voltages are coming through. but still no backlight
 
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larossmann

Administrator
Staff member
Do you have PPBUS_SW_LCDBKLT_PWR? If no Check LCD_BKLT_EN and BKLT_PLT_RST_L......


Let's stop a second. If he has 7.74v on PPVOUT_SW_LCDBKLT, that means Q9706/Q9707 are doing their job. I am guessing 7.74v means his multimeter batteries are dying more than anything else. A bad LED driver is the most likely case here.
 

larossmann

Administrator
Staff member
duke beat me to it. I went to get my food, I eat, I finish my post and he beat me. that dude is fast!!
 

aprendiz

Moderator
Sorry for that, my mistake, this happen when you answer the phone, repair motherboard and answer on forum, all at the same time, even I asked the voltage on D9701 twice.... Anyway, sorry...
 
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