My Auxiliary Power Supply for my GPU's failed. Here's my fix.

Dr. Stealth

macrumors 6502a
Original poster
Sep 14, 2004
812
713
SoCal-Surf City USA
My 450W Aux PSU mounted in my Optical bay started flacking out a few weeks ago. It worked fine for about 4 years driving my dual 680's. But I upgraded to dual 1080 TI's a while back and it brought that little PSU to it's knees. Under low loads all was fine but stack a bunch of (CUDA) renders in the queue and when those TI's were singing their sweet song at 99% load it started shutting my cMP down from GPU crashes.

I bought a backup 450W PSU (CD-Rom Bay Type) a couple months ago but since my first one had failed with the 1080 TI's and there are no more PSU's of that type available I really didn't want to replace the failed PSU with another cheap Chineese PSU that was nearly identicle.

What to do, what to do. I looked at my optical bay and all I had in there at this point was a failed 450W PSU and a Blu-Ray rom drive that had failed a couple years ago and I haven't missed it a bit.

I needed a new solution that would end the problem for good. I was looking for a "Bulletproof" solution.

Close the side panel and I still look bone stock. Nice !

My Solution:

I took some measurements of the optical bay and found a very nice standard ATX PSU that would fit. I bought an EVGA SuperNOVA 750W G2, 80+ GOLD PSU. I tied it's 120v input into my Macs PSU so everything turns on when I hit the power button. It may be over-kill but I'm back to work and those 1080 TI's are humming along under full load with no issues. This was actually a very nice Saturday afternoon project.

2s.jpg


1s.jpg


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DearthnVader

macrumors 6502a
Dec 17, 2015
889
4,857
Red Springs, NC
Sweet, as they say, necessity is the mother of invention, or doppers are inventive, whichever you prefer.:D

Don't see your PSU lead for the power bong, so that narrows it down.
 

shuto

macrumors member
Oct 5, 2016
63
32
amazingly neat setup. No extra power cable needed for external power supply, and just one on button for the whole system. nice!

Would be great if you could go into more detail with more photographs about how you connect the two PSU together. It sound like it was pretty straight forward for you to do, but it would amazing if you could explain it step by step.


(this is my solution for two internally powered 980ti in a MacPro...
https://forums.macrumors.com/threads/internal-powered-two-gtx-980-ti-in-mac-pro-5-1-for-octane-rendering.2057082/
but guess this wouldn't work with your monster cards)
 
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Tokaji_909

macrumors member
Nov 29, 2017
30
20
Zürich
Pretty cool mod :) Had that in mind too...
Only thing is: I'm not sure where you took the power for the external PSU from to make it switch on with the MAC.
Can you explain it a bit more detailed please?
 

TheStork

macrumors 6502
Dec 28, 2008
275
159
I, too, find this interesting enough to ask for more details.

I have several older, but good PSUs in my inventory that I can use for this purpose. I just need the wiring diagram to ensure a proper installation.

Did you have to jump several of the PSU's 20/24 pins motherboard plug to be always on (PC motherboard start-up/shutdown signal pins)?
 

Dr. Stealth

macrumors 6502a
Original poster
Sep 14, 2004
812
713
SoCal-Surf City USA
This is not a complicated mod at all. Simply jumping the two 120V wires of the Mac PSU to the Auxiliary PSU. We're talking two wires here. I am always reluctant to describe the mod in detail on this forum because if you can't figure out how to do this very simple mod then you probably shouldn't be doing it. No offense intended at all.
 
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JulianBoolean

macrumors regular
Aug 14, 2010
132
4
This is not a complicated mod at all. Simply jumping the two 120V wires of the Mac PSU to the Auxiliary PSU. We're talking two wires here. I am always reluctant to describe the mod in detail on this forum because if you can't figure out how to do this very simple mod then you probably shouldn't be doing it. No offense intended at all.
Well said. I know my limitations, and wouldn't attempt it. I wish there were some way to find techs who can do mods like this. Can't imagine I could take two 1080Ti's and an Aux power supply and drop it off at the genius bar in the Apple store. Even here in a large city like Chicago, I can't find somebody local to do mods like this.
 
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mattspace

macrumors 65816
Jun 5, 2013
1,221
942
Australia
I'm also interested, but wouldn't attempt the modification myself. Taking both power supplies to an electrician, would it be obvious to them what needs to be wired to what?
 

Tokaji_909

macrumors member
Nov 29, 2017
30
20
Zürich
I found out the pins and soldered it to the Main PSU. But I can fully test it, when I received my new GPU and have time to build it in...
 

Flint Ironstag

macrumors 6502a
Dec 1, 2013
963
520
Houston, TX USA
Well said. I know my limitations, and wouldn't attempt it. I wish there were some way to find techs who can do mods like this. Can't imagine I could take two 1080Ti's and an Aux power supply and drop it off at the genius bar in the Apple store. Even here in a large city like Chicago, I can't find somebody local to do mods like this.
Would be handy to have a nationwide network of techs who can handle stuff like this. Still, you're in Chicago. Check for some vintage stereo / amplifier repair shops. Or maybe there's a maker / hack space nearby you could pay somebody $50 and some beer.
 

William Payne

macrumors 6502a
Jan 10, 2017
927
353
Wanganui, New Zealand.
Would be handy to have a nationwide network of techs who can handle stuff like this. Still, you're in Chicago. Check for some vintage stereo / amplifier repair shops. Or maybe there's a maker / hack space nearby you could pay somebody $50 and some beer.
I would imagine it would be within the capabilities of people who repair electronics, like as you say steer and amplifiers.
 

Cuzzupino

macrumors newbie
Jun 20, 2018
24
2
This is not a complicated mod at all. Simply jumping the two 120V wires of the Mac PSU to the Auxiliary PSU. We're talking two wires here. I am always reluctant to describe the mod in detail on this forum because if you can't figure out how to do this very simple mod then you probably shouldn't be doing it. No offense intended at all.
I don’t understand. I don’t think that you knew how to jump cables before someone tell you how to do or somewhere where to study it. however, thanks for info, if U can tell more infos to do this job, thanks. If no, I want to learn and I will make some research or find someone that is able to explain very simple things...
 

crjackson2134

macrumors 601
Mar 6, 2013
4,486
1,618
Charlotte, NC
I don’t understand. I don’t think that you knew how to jump cables before someone tell you how to do or somewhere where to study it. however, thanks for info, if U can tell more infos to do this job, thanks. If no, I want to learn and I will make some research or find someone that is able to explain very simple things...
I think he explained it very well. Open both PSU’s, make a jumper connection between the 2 PSU’s AC input solder points, close up PSU’s, install back into case, plug in all connections, power on & use.

It really doesn’t take any further instructions.

Also I’m quite sure he knew how to do this without someone telling him. I would have. And if it didn’t power on at this point, I would then jumper the 2 pins on the ATX connector that some might use to force a signal to the PSU for power on. Obviously it wasn’t needed, so no extra explanation was needed. Anyone who has assembled computers for their own upgrades would or should already have this knowledge.
[doublepost=1529775953][/doublepost]
My 450W Aux PSU mounted in my Optical bay started flacking out a few weeks ago.
Nicely done. If I had the need, and no use for my opticle drives, this is the route I’d go too. It completely takes the strain off of th cMP. I actually bought a 850w Corsair PSU for this purpose, but never ended up needing it.
 
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tu2thepoo

macrumors member
Nov 14, 2017
70
58
I don’t understand. I don’t think that you knew how to jump cables before someone tell you how to do or somewhere where to study it. however, thanks for info, if U can tell more infos to do this job, thanks. If no, I want to learn and I will make some research or find someone that is able to explain very simple things...
I used to do this kind of soldering/modding when I had time to mess around with my computer, so I want to add some context to what Dr. Stealth is saying. The soldering itself is relatively simple, but that's only part of it - the other part is having enough experience to know that you have to avoid touching the capacitors, being relatively familiar with ATX pinouts so you don't somehow bridge the 5v DC connection with the 120VAC, that sort of thing.

People have injured themselves - shocks, burns, even cardiac arrest - messing around with things that have large capacitors. There's no real way to tell whether the people reading this thread are the type to read up on all of that beforehand, or are more likely to just jam a screwdriver inside and wing it.

Like crjackson2134 wrote, if you've done any wire modding/soldering for a computer project, you don't need much more guidance than what's already written. If you need more detailed instructions then you should probably start at the most basic level (e.g. soldering your own USB cables) then work up.
 
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Cuzzupino

macrumors newbie
Jun 20, 2018
24
2
I used to do this kind of soldering/modding when I had time to mess around with my computer, so I want to add some context to what Dr. Stealth is saying. The soldering itself is relatively simple, but that's only part of it - the other part is having enough experience to know that you have to avoid touching the capacitors, being relatively familiar with ATX pinouts so you don't somehow bridge the 5v DC connection with the 120VAC, that sort of thing.

People have injured themselves - shocks, burns, even cardiac arrest - messing around with things that have large capacitors. There's no real way to tell whether the people reading this thread are the type to read up on all of that beforehand, or are more likely to just jam a screwdriver inside and wing it.

Like crjackson2134 wrote, if you've done any wire modding/soldering for a computer project, you don't need much more guidance than what's already written. If you need more detailed instructions then you should probably start at the most basic level (e.g. soldering your own USB cables) then work up.
... is simple or no? If someone tell that is so simple I immagine that is simple also to explain... obiviosly this is not so simple... then I will go to write to some elettrical forum to find somehone that can explain me how to create a jumper.
Then I will try with some inexspensive hardware.. Thanks for the infos and sorry for my bad english... it is simple too but I know my limits... :)

First result in google “how to jump two PSU” : https://www.bit-tech.net/guides/modding/how-to-jump-a-psu/1/

Can You tell me if the guide above is good to follow for learn this mod?
 

Cuzzupino

macrumors newbie
Jun 20, 2018
24
2
I think he explained it very well. Open both PSU’s, make a jumper connection between the 2 PSU’s AC input solder points, close up PSU’s, install back into case, plug in all connections, power on & use.

It really doesn’t take any further instructions.

Also I’m quite sure he knew how to do this without someone telling him. I would have. And if it didn’t power on at this point, I would then jumper the 2 pins on the ATX connector that some might use to force a signal to the PSU for power on. Obviously it wasn’t needed, so no extra explanation was needed. Anyone who has assembled computers for their own upgrades would or should already have this knowledge.
[doublepost=1529775953][/doublepost]

Nicely done. If I had the need, and no use for my opticle drives, this is the route I’d go too. It completely takes the strain off of th cMP. I actually bought a 850w Corsair PSU for this purpose, but never ended up needing it.
It is nice that some people born with knowledge how to jump cables... It is so simple... I hope to reborn again with more knowledge... ... if not I can’t learn a so simple thing...
[doublepost=1529847340][/doublepost]Can this help?

http://www.add2psu.com/store/
 

Cuzzupino

macrumors newbie
Jun 20, 2018
24
2
Education + Experience = Knowledge. Good luck being born with it.
... unfortunally I’m not born with experience or education... what a strange case! I can only study and ask to right people to reach the knowledge..

In all this post I learn that to jump two psu we need to open and jump two psu over 120 volt... that is the only thing to know from people that already know what to do... so strange.. what a closed circle. The rest to do must be in my dna.. nobody respond to one of my question in exaustive way. Keep your secrets matured in you car garage.. I will go alone. I assembled computers for years with no use of soldering... I think that I will go to my car mechanics. Thanks.
 

h9826790

macrumors G5
Apr 3, 2014
12,766
5,577
Hong Kong
... unfortunally I’m not born with experience or education... what a strange case! I can only study and ask to right people to reach the knowledge..

In all this post I learn that to jump two psu we need to open and jump two psu over 120 volt... that is the only thing to know from people that already know what to do... so strange.. what a closed circle. The rest to do must be in my dna.. nobody respond to one of my question in exaustive way. Keep your secrets matured in you car garage.. I will go alone. I assembled computers for years with no use of soldering... I think that I will go to my car mechanics. Thanks.
TBH, unless you need to power more than two 1080Ti (500W in total). I really can't see why you want to go for this extra PSU mod, but not the pixlas mod.

The cMP PSU is rated 980W, more than enough to power any single GPU card.

If you want to do any solder job, why not just solder a cable to get direct power from the PSU? but make it so complicated to jump another PSU?

In fact, the Pixlas mod doesn't even need to solder anything, that's so much easier (and safer) than connecting two PSU together (at least true on the cMP).

And this is a very nice and easy to follow guide about how to apply the Pixlas mod.

http://thehouseofmoth.com/mac-pro-pixlas-mod/
 

Cuzzupino

macrumors newbie
Jun 20, 2018
24
2
I want to know for my personal growth.
However thanks for info.
I know very well that mac psu can handle 900+ watt. And ear about pixla mod. I will see also this guide. The day I will go two psu jumped. I will try to make a guide also.. at the moment only the pixla guide as got some nice person that write it, his must be miscredent eretic that offend the natural knowledge of all us at first day of life... but still fit to me... I hope in future I will be able to find a guide (like pixla) also for the mod with two psu jumped.

Atm I will go with one dual mini 6 pin to 8 pin and an 8 pin female to dual 8 pin male (16 awg cable) that seems to me the best compromise in term of safety, power distribuition and to let free slot for other internal device, How I learn in this site from an user that I don’t remember name. My way instead is the one that i described above in first post but too much cables...