MacBook Pro A1398 820-3787-A - Permanently Disable Discrete GPU

[dezmiz]

Hello!

I'm trying to permanently disable the dGPU (NVidia GT 750M) in my late-2013 MacBook Pro Retina (A1398 820-3787-A). I can get the system to boot up using the nvram variable "fa4ce28d-b62f-4c99-9cc3-6815686e30f9:gpu-power-prefs=%01%00%00%00", and can prevent the OS from switching to the dGPU via a handful of different methods (e.g. via OpenCore + WhatEverGreen or spoofing the device properties), but the discrete chip seems to stay powered up and cause the machine to overheat. I'm hoping to accomplish something similar to this hardware modification for a 2011 MBP: https://realmacmods.com/macbook-2011...n-gpu-disable/

In that mod, the removal of one resistor (R8911) prevents the dGPU from powering up. I am curious if there's such a resistor on my own logic board that I might be able to remove for the same effect. I'm a relative layperson when it comes to such board modifications, but from looking at the boardview and schematic for 820-3787-A I think that R9301 might be what I'm after... ? Other candidates I've considered are R9300, R9210, R9211, R9623, and R8701.

Can anyone take a look at the boardview/schematic and tell me if I'm on the right track or if such a thing is even possible with this board? Any help is much appreciated. I've attached a zip of the boardview and schematic - my apologies if that is not allowed in this forum.

[karmele]

Re: MacBook Pro A1398 820-3787-A - Permanently Disable Discrete GPU

Hi, I´ve compared with my PDF and BRD board and I would say that in your case is the R9301.
It is the one that makes sense because it is the R that goes to de PVCC.
Regards

[violaboy13]

This was my solution to disabling dGPU on a A1398 820-3787-A board.
1. Jumper from LCD_MUX_SEL via to C1099 pin 2 (Pulls to ground)
2. Jumper from pin 1 R9626, pin1 R9627 to pin 1 C9700. (Provides voltage)
3. Jumper pin 11 U9700 to pin 2 C9700 (Pulls to ground)
4. Remove R9623 (Remove pull down resistor)
5. Jumper pin 1 R5335 to pin 1 R7780 (Turn backlight on after sleep)
6. Remove inductors L9330, L9360 to entirely disable the dGPU so that MacOS doesn't see it and the dGPU won't show up in system information.

My only issue after this workaround was that I was no longer able to control brightness for the display. Backlight was at max all the time.

[mon2]

Varying with the backlight design, you can build a very low cost and tiny circuit to output a PWM and/or SMBUS commands to dial the backlight to your liking.

For example, review the very low cost ($0.10 USD in small qty) RISC-V microcontrollers by WCH. Full toolchain is available with excellent starting project examples for such topics.

Post back if you are interested to build such a tool. The development kits to get you started are < $ 10 USD on Aliexpress - includes a working board & JTAG tool (is actually a SWD - single wire debug).