820-2915 graphics problem

No-Clean

Member
Board had the GPU replaced about 2 years ago and worked fine till now, when it came in and it had the typical GPU issues so I replaced the GPU with the same
216-0810084, this time the computer booted up but some areas of the image show lines and weird colors, I then put a new-other GPU and same issue, I also replaced C9560 but I am stil getting 1.3v on
PP1V5_GPU_REG, any pointers will be appreciated.
 

2informaticos

Administrator
Staff member
C9560 is not a problem in this board.
And 1.35V is correct voltage for vRAM.

Same issue on external monitor?
Could be now bad solders/traces under vRAM chips.

Is almost impossible to get real "NEW" chip for these; better to disable GPU...
 
Last edited:

No-Clean

Member
I just got about 4 of this Macs from people who don't have money to buy new computers and they want me to fix them even by disabling the GPU, so far I am successful doing this with 820-2915-B by following this steps:
  • Doing this will disable external image to a monitor
  • Adjusting brightness can only be done via software with an App called QuickShade and a version compatible with 10.13 or below, the current one in the App store wont work.
  1. Set LCD_BKLT_PWM (R9704) to 3v with jumper from PP3V3_S0 (R5650), this solves problem when opening lid shows no image.
  2. Remove R8911 to remove power to GPU
  3. Load modified BIOS to disable GPU
  4. Select a startup disk
  5. Add a firmware password “GPU” so an SMC reset won’t disable this "hack"

Now on boards 820-2915-A those same steps wont work, any pointers will be greatly appreciated.
 

No-Clean

Member
I know that there is the Tiresias (the GPUkiller) that makes this easier, but I am trying to see if I can get away by doing it just with changing hardware configuration and changing BIOS.
 

2informaticos

Administrator
Staff member
I never looked at A/B board version.
I did maybe 10 in this way.
Few months ago I started to do it reflashing GMUX.
 
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