Janky Intel Mainboard mod to enable iGPU on a board without iGPU power rail

[blissed]

So the goal is to supply vccgt on a mainboard that doesn't have a vccgt rail.

Board: Fujitsu D3373-A11

Why: I want to use software features that rely on the iGPU, and for that the iGPU needs voltage - Intel spec is 1.05V

Why not use another board?:
I'm in Germany and idle power is of crucial importance and fujitsu boards are very efficient do to good bios support for c-states and 12v only PSU.
Check out this idle power ranking from hardwarelux:
https://goo.gl/z8nt3A
Also the board is very cheap and the bios can be modded to support up to Intel core 9th Gen.

Anyway the board does not have an iGPU rail but its  got everything else I want...

The Plan:
This is the pinout for socket
https://en.wikichip.org/wiki/File:skylake_pin_diagram.png
The grey lower left is vccgt, which is the iGPU rail


The main issue is that there is only one place I can connect to, to supply the voltage and that are vias on the backside of the socket



So as you can see the vccgt vias are surrounded by vcore infill.

Issue 1:
So the plan would be to xacto knife cut the vcore infill surrounding the vias of from the vcore power plane. Scrape of the solder mask and use the cut off vcore infill (now it would be not connected to anything) and use it as vccGT powerplane.

Issue 2:
Now I'd have a exposed vccgt plane to solder to, but there is still no vccgt rail... So the plan is to use Vmem from the ddr4 vrm 1.2v its closest to the 1.05v Intel spec and powerful enough



So I'd double or triple the filtering cap on the memory vrm and connect a wire to the 'new vccgt plane'


Also I'd preferably drop the voltage 100mv, I thought maybe a schottky diode but I like some advice. Max amperage should be 20A. typical 1A - 10A

Issue 3:
I'd like filtering mlc's at the new vccgt plane but the only ground anyware close is at the through hole caps from the vcore vrm. So I'd run a copper foil from the ground pin at the vcore caps to right beside the new vccgt plane and than add same mlc's across.

Issues 4:
Power sequencing - I don't really have an answer to this issue I can't find a Intel skylake power sequence diagram. Maybe someone knows something about it...

So if you people can advice me if the plan is sound or if I missed something.

Thanks for helping

[amyk]

1.05 and 1.2 may seem close but so are the tolerances on these modern CPUs.

The memory normally uses far less power, so I'm not sure how the VRM for it will be able to supply the GPU load.

There's also the question of whether it needs any other circuitry to enable the GPU beyond just supplying power, and then you have the software side to deal with too.

I think what you're trying to do is more hardcore than 99% of everyone else here, so good luck.

[blissed]

Thank you for your response

I feel like this mod is pretty straight forward and not that hardcore, I'd say the nintendo wii wft trim is a hardcore mod.

Anyway intel's spec for vccGT absolut maximum is 1.5V so there is some headroom, but yes i'd like to drop the voltage 100mv, but i haven't found a good way to do that, yet

The memory vrm uses a 0902nsi low side fet from Infineon
https://www.infineon.com/dgdl/Infineon-BSC0902NSI-DataSheet-v02_04-EN.pdf?fileId=db3a30433072cd8f01308ea027703424



and since the buck converter drops 12 to 1.2 the low side does most of the work anyway I feel pretty good about the current handling even with the igpu

Intel specs the igpu in absolut maximum current at 45A depending on model.

My xeon is 45Watt Tdp so i'd say its a fair guess that it wouldnt pull 45A rather maybe 25A at worst and ddr4 with 4 dimms will not exceed 15A - so I add a headsink to the high and low side fet's to be on the safe side.

the software side is a considferation but i'm optimistic, the bios has a vbios file

[blissed]

So I started removing the solder mask and found some ground vias in between the vccgt vias
So I have to drill out some vias, but it solves my ground plane for mlcc



White is ground, yellow is vccgt an purple marks vias that have to be drilled out

[blissed]

For anyone wondering it worked

[dmendesf]

Congratulations!
Btw I googled "nintendo wii wft trim" and my jaw dropped. WTF?