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MP 1,1-5,1 Mac Pro Mojave GPU power leads - Hard shut downs

Boomish69

Boomish69

macrumors 6502
Original poster
Sep 13, 2012
402
109
London
I upgraded my Mac Pro 5.1 to Mojave, it kinda went smoothly but once under load the Mac did a few hard shut downs , I noticed the fans were a bit erratic and after a day searching, checking temps, and investigation I've installed Macs Fan Control and reset the SMC a few times..the fans now seem stable but I'm scared to run another power hungry app.

I'm worried about my MSI Twin Frozen iii 7850 drawing too much power and tripping the PSU, it says it draws 130w, now I should get 75 from PCIE and 75 from the single 6 pin connector. But I don't think the PCIE power is guaranteed, so I thought I grab a dual 6 pin to single 6 pin GPU power to combine the two lots of power form the Mac Pro, but I can't find 1 anywhere, is this possible? am I searching for the wrong thing?

Now I'm wondering about giving up and getting a Rx 560 that only draws 75..

Appreciate any help.
 
Your HD 7850 is quite possibly just old and wearing out. The DUAL Mini 6 pin to ONE x 6 pin certainly won't hurt and if you run an EVGa PowerLink it might just fix your problem but really... your 7850 is really old now.

Problem could also be a broken spring rivet on your Northbridge heatsink.

Any red LEDs on your CPU tray after bootup ?

Is ALL of your RAM showing up ?

My MSI RX 580 8gb currently running on a 24" Mitsubishi monitor Display port to DP>HDMI adapter to HDMI on monitor which gives me HDMI Audio without the need for 3rd. party kexts is busy on YouTube videos and appears to be using 21 WATTS according to iStats Menus vers 6.40.

Why get an RX 560 ? For what you get the Sapphire Pulse or MSI Armor RX 580's 8gb are more then worth the extra cost . . .and. . .they are getting cheaper.

As I hardly ever use Windows I don't miss the EFI bootscreen of my flashed Sapphire DUAL-X HD 7970 but it is nice to have it as a backup and it is metal supported. I take very good care of it.

At the very least, the oldest but EFI flashable and Metal supported card is the HD 7950 by Gigabyte best.
 
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Thanks Mike, that makes total sense, the 7850 hasn't been used much, I think it was spare I had from setting up PC's for the kids, I just had forgotten about the 580 it was crazy expensive last I looked..
Thanks for the feedback
 
Boomish69 said:
Thanks Mike, that makes total sense, the 7850 hasn't been used much, I think it was spare I had from setting up PC's for the kids, I just had forgotten about the 580 it was crazy expensive last I looked..
Thanks for the feedback
Click to expand...
Out of interest .. are you on bootrom 144.0.0.0.0 ?
 
That's very good indeed.

Please post after you get your dual Mini 6 pin to 6 pin cable.

Also , try cleaning your GPU's PCI contacts with a clean, soft eraser.
 
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One can use a combined adapter solution.
Dual mini 6 to 8 pin. Then 8 pin to double 6plus2.
I do that for 6 and 8 pin GPUs, but why not for double 6.

In theory it makes no sence as 6 pin is 75 Watt but who knows.

Time for monitoring the real power draw of the connectors.
 
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Macschrauber said:
One can use a combined adapter solution.
Dual mini 6 to 8 pin. Then 8 pin to double 6plus2.
I do that for 6 and 8 pin GPUs, but why not for double 6.

In theory it makes no sence as 6 pin is 75 Watt but who knows.

Time for monitoring the real power draw of the connectors.
Click to expand...
Genius thanksMacshrauber, I still can't find a dial 6pin to single 6 pin anywhere..
 
Boomish69 said:
Genius thanksMacshrauber, I still can't find a dial 6pin to single 6 pin anywhere..
Click to expand...
Yes, I couldn't find a DUAL Mini 6 pin to 6 pin either but in any case that cable would only help if you also bought and connected the cable to an EVGa PowerLink which BALANCES the total power fed into it prior to passing it all to the GPU.

8 pin cables pass more power than 6 pin cables and seeing that the HD 7850 only has one 6 pin socket the ONLY benefit you would get would be " balanced power ".

I think it's time to look elsewhere for the cause of your shutdowns eg: PSU - Northbridge spring rivets - overheating due to accumulated dust & grime - RAM & the RAM contacts etc.

I would recommend removing ALL PCIe cards except your 7850, re-seat your RAM.

Do a THREE consecutive NVRAM reset.

Study up on the cMP's diagnostic LEDS on both the motherboard and the CPU tray.

Remove your PSU ( 4 screws - not hard, just tedious ) blow out all dust.

Get iStats Menus ( it has a trial period ) post a screen grab of ALL your operating temps & power settings here ( Preview has a "Take screenshot" function in it's FILE dropdown menu.

Do you have ANY other AMD GPUs lying around ? Doesn't matter if they are not flashed.

================================================

If I were you . . and wanted to have EFI booting & Metal support & wanted to rule out GPU caused shutdowns
I would buy the following ..

For EFI booting.
Either a Sapphire Dual-X HD 7950 or HD 7970 = more powerful.
The HD 7950 / RX280 or better a HD 7970/RX 280X. ( both have 6 & 8 pin sockets ) plus they can be EFI flashed ( I can help you with that ) and are both Metal supported and if you bought any of these cards at least you could rule out GPU problems.

The above cards are a big step up from your HD 7850.

I have a downvolted EFI flashed Sapphire DUal-X HD 7970 3gb. which performs flawlessly in High Sierra & Mojave since I replaced the two fans. I run it's INPUT power through an EVGa PowerLink =

TO the Powerlink
(1) Dual mini 6 pin to 8 pin https://www.amazon.com/COMeap-Express-Video-Adapter-15-inch/dp/B07J336WY4

(2) Dual SATA to 6 pin ( The Powerlink has two 8 pin input sockets )
https://www.amazon.com/Cable-Matters-2-Pack-SATA-Power/dp/B01DV1Z4X2

From the PowerLink to the GPU
( Note : EVGa includes a spare 6 pin male socket for power OUTPUT )

(1) ONE x female 8 pin to ONE male 8 pin to the GPU 8 pin input socket.

(2) ONE x female 6 pin to ONE x male 6 pin to the GPU 6 pin socket.
=============================================

Later you could for just more speed, much lower TDP and Metal support ..
buy either a Sapphire Pulse RX 580 8gb or the MSI Armor equivalent.
 
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It's very easy to solder up your own dual mini 6-pin to whatever your card uses. I made my own cable. Dual mini 6-pin in, all +12V leads soldered together, all grounds soldered together. That breaks out to a singe 8-pin.

There's nothing magical here. Just + and -.
 
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tpivette89 said:
Also, if you wanted a link to the ebay seller I used for this cable, here you go. He still has them in stock:

https://www.ebay.com/itm/16AWG-Dual...794532?hash=item5b4f242be4:g:djEAAOSw7R9b5PZB

Hope this helps.
Click to expand...

I’m also using the same power cable on a RX570 8gb graphic card and working fine. It was a friend of mine who gave the tip that I need the dual 6-Pin to single 8-Pin cable and luckily did not encounter any issues the first time the RX570 was installed.
 
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Excuse the delay getting back to all the messages, that amazing help thank you all, I've managed to stop the hard shutdowns simply by re-doing the PRAM rest and installing the Mac's Fan Control software, now the Mac Pro seems to be behaving ok, the fans are quiet again, although they rev occasionally under load but it's behaving. I'm still saving up for a RX 580..:)
 
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