Janky Intel Mainboard mod to enable iGPU on a board without iGPU power rail  - Page 1
Forum section: electronics / projects

author: blissed
author_rank: Newbie
timestamp: October 18, 2023, 03:07:01 pm
content: So the goal is to supply vccgt on a mainboard that doesn't have a vccgt rail.Board: Fujitsu D3373-A11Why: I want to use software features that rely on the iGPU, and for that the iGPU needs voltage - Intel spec is 1.05VWhy 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/z8nt3AAlso 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 sockethttps://en.wikichip.org/wiki/File:skylake_pin_diagram.pngThe grey lower left is vccgt, which is the iGPU railThe 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 socketSo 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 enoughSo 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 - 10AIssue 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

author: amyk
author_rank: Super Contributor
timestamp: October 20, 2023, 04:08:15 am
content: 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.

author: blissed
author_rank: Newbie
timestamp: October 20, 2023, 03:42:04 pm
content: Thank you for your responseI 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, yetThe memory vrm uses a 0902nsi low side fet from Infineonhttps://www.infineon.com/dgdl/Infineon-BSC0902NSI-DataSheet-v02_04-EN.pdf?fileId=db3a30433072cd8f01308ea027703424and 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 igpuIntel 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

author: blissed
author_rank: Newbie
timestamp: October 20, 2023, 04:00:21 pm
content: So I started removing the solder mask and found some ground vias in between the vccgt viasSo I have to drill out some vias, but it solves my ground plane for mlccWhite is ground, yellow is vccgt an purple marks vias that have to be drilled out

author: blissed
author_rank: Newbie
timestamp: October 26, 2023, 08:36:10 pm
content: For anyone wondering it worked

author: dmendesf
author_rank: Frequent Contributor
timestamp: October 27, 2023, 12:27:42 am
content: Congratulations!Btw I googled "nintendo wii wft trim" and my jaw dropped. WTF?