MacBook Pro 2012 Non Retina no Video output

[Roman78]

Hello there....

i got a MBP 2012 from a friend of mine with some Video problems. It just don't show anything internal nor external. The MacBook self is working and can be reached from the Network using Screen Sharing.

So here is what i discovered till now and i hope someone can help me a little bit. I am not that experienced in repairing such small hardware. So i got my self the schematic and the boardview of this model. It is the 820-3330A by the way and i watched some Rossmann Videos.

I measured the GPU Voltages and i discovered that PPGPUFB_S0 is a little bit to low....well it has to be 1.5 and it is 0.025V

These is what i measured:
PP3V3_S0GPU_FET 3.3V = 3.334V
PP3V3_S0GPU 3.3V = 3.331V
PP1V8_S0GPU 1.8V = 1.790V
PPGPUFB_S0 1.5V = 0.025V
PP1V05_S0GPU 1.05V = 1.048V
PPVCORE_GPU 1.0V = 0.902V

In the screen dump from the circuit board these are all PPGPUFB_S0 points purple. So the Memory just don't get any power. The other Picture, somehow is smaller than i tried to upload, is the are of the board.

[piernov]

Re: MacBook Pro 2012 Non Retina no Video output

What has been done to the board?

[Roman78]

Re: MacBook Pro 2012 Non Retina no Video output

Oh, according to my friend it went to two different companies to fix the problem. One at least changed the GPU (old gpu came in package), and i also think they changed the VRAM. At least it looks a little bit like that on the board. And i see a lots of small scratches on the picture, so they also measured the voltage there.

Now he send it to me, because i do some hobby based repair and he just bought another one.

[piernov]

Re: MacBook Pro 2012 Non Retina no Video output

This probably had unrepairable graphics issues originally, and now may have secondary issues due to GPU and VRAM having been messed with, hence the missing VRAM power rail. The work on the VRAM area doesn't look very clean, I guess they only tried to reflow it (but edge bonding hasn't even been cleaned properly).

Was this liquid damaged though?

Only thing I can think of to save this board would be to bypass GMUX, working with Intel iGPU only. No external display support and no brightness adjustment though. You can at least try to set the gpu-power-prefs EFI NVRAM variable if you have remote access and SIP is disabled.

[Roman78]

Re: MacBook Pro 2012 Non Retina no Video output

hmmm can i use the exact same gpu-power-prefs like from the 2011 model? I modded a lot of those. And i think i also have to remove a resistor to power down the gmux.

I used this mod on the 2011 models: https://realmacmods.com/macbook-2011...n-gpu-disable/

and made a German DIY of it: http://www.die-oswalds.de/blog/2019/...m-und-loesung/

My friend did not tell me anything about a liquid damage. So i think there was none.

[piernov]

Re: MacBook Pro 2012 Non Retina no Video output

The same EFI NVRAM variable tweak should work the same. Note that this is not a permanent fix as a PRAM will clear it and an upgrade could clear it too, so that's not a good solution for a board "out in the wild". (setting an EFI password can help preventing "accidental" PRAM reset but that's it)
The resistor is typically removed to disable the GPU VCore buck converter, as it's useless to supply power to a unused GPU.
The bridge for the backlight PWM line is used for High Sierra and up, where otherwise there is no backlight after sleep and other related issues. I don't know if it's the same for 2012 model though.

[Roman78]

Re: MacBook Pro 2012 Non Retina no Video output

So finally i had some time, but no success.

I booted the machine using a USB GPU and that worked fine. I tried to edit the NVram values, but the internal screen stays blank. Also i noticed the white standby LED flashes some times before the chime.

I still could try to remove the resistor to cut down the power. But at this moment i don't now which one.

/edit: I just experiment a little and figured out when removing resistor R8900 the dedicated GPU will disappear from the Hardware System information. But still no internal screen.

[Roman78]

Re: MacBook Pro 2012 Non Retina no Video output

Its working...

Had to add one more nvram entry to get it working.