820-3787: No image on display

Have this board, no liquid damage or corrosion. Came in for no image on display, but when i first power it on, it worked just fine until I changed the energy saving setting to always use the AMD GPU and not the Intel. As soon as I made the change, and it switch to black screen.
i was going to replace U9600 but decided to replace U9300 first which didn't fix it.

My question, can i use a U9600 chip from a 820-3332 or 820-00426 board or as an alternative, i can purchase this chip from DigiKey.com?
On the schematic, apple part numbers 341S3565 and 337S4313 match on both the 3332 and 3787. Plus the spec info from BOM page matches DigiKey.com.
 

2informaticos

Administrator
Staff member
U9600 has firmware, but I don't know untill which point is board dependant.
New chip probably will not serve...
 
So replaced U9600 with one from the same board. Same outcome. I did noticed that LCD_PWR_EN is 0V, while PPVOUT_S0_LCDBKLT is about 50v. Any suggestion?
 

2informaticos

Administrator
Staff member
50V on backlight output means open LED strips.
Bad LCD connecotr, video cable, or display.
If you get that voltage, image should be there too.
Did you check external video?
 
No video on external display or on another known good display.
Also fan ramps up to max. Ive tested with another frame to confirm issue isn't with keyboard or trackpad.
 
So before pulling U9600, since i still had the original one, i installed it into the donor board (which didn't originally have video issue) and the chip works. So now i'm lost again as to where to go from here
 

2informaticos

Administrator
Staff member
If problem appeared after set GPU as default, should be GPU issue.
USB activity also confirms board booting and only video is bad.
Good luck to find a good GPU...
 
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