One GPU One Cpu Cooling - P375SM

Hello, long story short - I have p375sm (specs below) mainly used for designing so I only need one gpu installed.

(p375sm) specs:

• Intel® Core™ i7-4930MX Processor Extreme Edition
  
  
• 8GB NVidia GeForce GTX 980M DDR5
  
  
• 2x Kingston Technology HyperX Impact 16GB Kit 1600MHz DDR3L CL9
  
  
• 2x Samsung 850 EVO - 1TB - mSATA Internal SSD in raid0
  
  
• 2x Samsung 850 PRO - 2TB - 2.5-Inch SATA III Internal SSD

I was wondering if I can utilize the other gpu fan (which is just setting there) to cool the cpu by using p370em cpu heat sink that comes with three pipes, if yes how can i do that? and how can I run the 2nd gpu fan for the cpu.




If anyone has an idea or tried this before please chime in,,, Thanks.

 

It will all physically fit (the EM used a plastic spacer for the single GPU models to help support the arm in front of the 3rd fan so you are aware).

The EC on yours wont expect to use the third fan without the 2nd GPU is my only concern. You could grab the fan and plug it in and see if it spins during load. If it does you are good to go.

 

Thank you Meaker for your response, the fan for the 2nd gpu is already installed and hooked since day one by default. but never spin I assume it requires the 2nd gpu card to start, so in order to make it start,it needs to be connected somewhere else. the question is WHERE?

 

The EC should prompt the fan to spin according to the second GPU's temperature reading, therefore that third fan probably won't spin unless you install said GPU.

I don't think there's another header for that fan, nor a way to force it to spin without another card for it to cool. You could try connecting it and using FN and 1; those hotkeys toggle max fans on and off.

 

Yes, it needs a signal for gpu temp and, perhaps, also one for 'MXM2-present'.

You could fake that by duplicating the signal of the primary gpu. It isn't as clean as using the cpu's thermal signal, but at least it is doable, whereas with the cpu the signal is embedded in a single, multiple-use pin (see Platform Environment Control Interface). So ... solder wires between both MXM sockets' pins #32, #34 and optionally pin #2 as well. These three should be sufficient to get the 2nd gpu fan to start and then run in sync with the primary gpu fan:

Spoiler: MXM thermal and present pins

These things use very little power, so it should be no problem at all to divide them. Try only #32 and #34 (SMB_DAT and SMB_CLK) at first; they seem to be hooked directly and the EC may simply be written to only take into account temperature, rpm and fan voltage, without any checks as to whether there actually is a cpu or gpu present (you don't really need to, so why bother complicating the software?).

Granted, the pins are a bit small, so ... an alternative is tapping into the voltage wire of the cpu fan and make it run both fans at once:

Spoiler: Clevo P37xxM - dual fan mod

The picture is for the combination gpu-1+gpu-2, but it might be better to make that cpu+gpu-2, that way it will run when the cpu could use the additional cooling. That will also be the benefit over the mxm mod, but the disadvantage is that you may loose a bit of oomph at the higher end due to current draw limitation, although the voltage-control chip itself should be able to handle it (more-or-less). At the lower rpm range it wouldn't make any difference as it'd simply draw more current in order to set the voltage requested by the ec (it'd be like trying to power a single, very sluggish fan).

 

If I may also add, a dying/not-working GPU even disabled in windows will trigger the second fan as well. All three fans spin with my dead 780M in the second slot, so if you cannot or are unwilling to do that mod, a cheap mostly-dead GPU off ebay may be up your alley (though I'd get the slave GPU heatsink just in case; even with little power in it and SLI disabled system-wide and the card disabled in device manager it could possibly still overheat and cause damage).

 

Technically its a straight forward application and that's the easy way to go with less troubleshooting hassle, but takes some workshop to do

 

Thanks a lot for this great and generous effort, that's the kind of approach I was thinking of and looking for,,, connecting cpu+gpu-2 is the way to go now I only need a vacation to start such a project, because i need this baby for work these coming days.

 

Could you cut the wires and splice into the normal CPU fan? the PWM signal to control CPU fan speed shouldn't be affected by the extra load of the extra fan if I understand how it works correctly?

 

These are 3-pin fans, so there's no pwm wire at all. There's voltage, ground and 'sense', which is hooked to the fan's tachometer (for rpm reporting). If there's no signal on that wire then it triggers the 20-beep-warning-then-shutdown in the ec; check by holding back the fan while the system is running.

Anyway, since there's only voltage control there's a limitation on the supplier's side. But for a 4-pin/pwm-fan it'd be the same bottleneck; the pwm wire tells the fan how to run (010101 or 001001 ... for instance), so it'd draw power from the voltage wire intermittently. With these fans you'd have to split off the pwm wire as well, otherwise the 2nd fan would run 100% all the time. Downside is that you'd be stacking the draw since both fans will run-and-stop in sync.