820-4924 no backlight

arnonabuurs

New member
Hi guys, this one has got me going crazy..... So i have an 820-4924 with no backlight, usually my favourite repairs. Sometimes it works for a day and then its off again. Board looks superclean. Changed the display cable as these are not good in many cases, same issue. Changed the display for a know working one, same issue. 38-49v on the connector, so it has voltage. So I assumed it was inside the connector, which i eplaced, still the same issue. Is there any othe voltage/dataline i need to get backlight besides PPVOUT?
 

2informaticos

Administrator
Staff member
39V is the correct voltage.
49V means open line to LED strips on the screen.

Do you always get image, only missing backlight?
Check I2C_BKLT_SCL/SDA and EDP_BKLT_PWM lines.
You should get o-scope activity when pressing backlight adjust keys.
 

arnonabuurs

New member
39v is with the original display installed. 49v i got with my testing display, that is actually cracked. Yes its always missing backlight, not a black display. When i turn it on display shows. I close the lid, open it again and the backlight is off. With a flashlight I can see the login screen. When i press the backlight adjustment keys the screen actually seems to blink. Will check these 2 lines now, what diode mode reading should these have?
 

arnonabuurs

New member
I have 3.3v on BKLT_EN_R
on pin 3 & 4 5v on both with no display
On pin 3 -> 5v and pin 4 -> 3.1v with original display connected
Does that say something?

o-scope I have to do monday not at hand.
 

2informaticos

Administrator
Staff member
Wait, do you get normal image (with backlight) at first start?
Original Apple Magsafe 2 85W charger tried?
Do NOT use 1-->2 adapter for this machine!
Also try disconnecting internal SSD; use USB OSX.
 

JohnB8812

New member
Your test screen is the wrong screen so only use the broken one. At 39 volts it should work..measure SMC_LID when it doesn?t work
 
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