Dears, this is my first post here and first try to fix my own laptop Apple MacBook Pro Retina 15-inch Mid 2015.
I have some general electronics troubleshooting experience and still as my hoppy but this is my first laptop trying to fix.
History: my laptop backlight stopped working without any reason.
Symptoms:
I have image on screen using my flashlight.
I have fully working laptop with the help of my external SAMSUNG LED tv via HDMI cable.
Keyboard backlight still working and can be adjusted normally.
Since two days I tried to follow all similar issues here this forum and still in the same place.
Tried to test with another "used" 820-00138 logicboard brought from ebay but still no backlight. Could be the same issue (faulty U7701)??
From first visual inspection there is no any sign of liquid damage nor corrosion nor any sign of component failure.
I followed the schematics carefully and there was nothing wrong with all measurements in LCD Backlight driver circuit.
Here are the volt readings as I still remember on U7701 :
1,2=0v
21=0v
5,18=5v
9,10,11=12v
17=3.3v
PPVOUT_S0_LCDBKLT=0v
PPBUS_S0_LCDBKLT_PWR_SW=0v
PPBUS_S0_LCDBKLT_FUSED=12v
PBUS_SW_LCDBKLT_PWR=12v
I followed all measurements on LVDS connector (J8300) and was fine I guess except this pin #8 (LCD_BKLT_PWM_R) which I think not normal:
When I power on the laptop there is another chip pulls down this pin to 52Ohms, but it is open circuit in power off mode. I checked with / without LVDS cable and the same behavior.
From my own primitive experience, I think (U7701) still needs some information from another chip (i2c I guess) to start boosting.
FYI, main LCD is normally detected by OS and tried SMC and PRMA reset but nothing changed.
Could anybody help in this case ?
I have some general electronics troubleshooting experience and still as my hoppy but this is my first laptop trying to fix.
History: my laptop backlight stopped working without any reason.
Symptoms:
I have image on screen using my flashlight.
I have fully working laptop with the help of my external SAMSUNG LED tv via HDMI cable.
Keyboard backlight still working and can be adjusted normally.
Since two days I tried to follow all similar issues here this forum and still in the same place.
Tried to test with another "used" 820-00138 logicboard brought from ebay but still no backlight. Could be the same issue (faulty U7701)??
From first visual inspection there is no any sign of liquid damage nor corrosion nor any sign of component failure.
I followed the schematics carefully and there was nothing wrong with all measurements in LCD Backlight driver circuit.
Here are the volt readings as I still remember on U7701 :
1,2=0v
21=0v
5,18=5v
9,10,11=12v
17=3.3v
PPVOUT_S0_LCDBKLT=0v
PPBUS_S0_LCDBKLT_PWR_SW=0v
PPBUS_S0_LCDBKLT_FUSED=12v
PBUS_SW_LCDBKLT_PWR=12v
I followed all measurements on LVDS connector (J8300) and was fine I guess except this pin #8 (LCD_BKLT_PWM_R) which I think not normal:
When I power on the laptop there is another chip pulls down this pin to 52Ohms, but it is open circuit in power off mode. I checked with / without LVDS cable and the same behavior.
From my own primitive experience, I think (U7701) still needs some information from another chip (i2c I guess) to start boosting.
FYI, main LCD is normally detected by OS and tried SMC and PRMA reset but nothing changed.
Could anybody help in this case ?
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