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clevurguy

macrumors newbie
Original poster
Feb 7, 2020
1
0
Trying to upgrade Graphics Card. GT120 and system (4,1/5,1 High Sierra) works fine, but when I swap it out for a AMD Radeon HD 7950 (mac addition) it chimes, fans spin but blank screen. (no boot or anything.)
using a Dell Ultrasharp U2718Q monitor through mini port (not sure if that matters.)

I have the 2 cords for extra power plugged into it working.. what am I missing?

thanks in advance! i’m pulling my hair out. ha.
 

MIKX

macrumors 68000
Dec 16, 2004
1,815
689
Japan
This might help.

Shut down, remove ¥the power cord for a couple of minutes and do the 3 Chime NVRAM reset........

NVRAM_PRAM_ResetMac.jpg
 
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Macsonic

macrumors 68000
Sep 6, 2009
1,706
97
Trying to upgrade Graphics Card. GT120 and system (4,1/5,1 High Sierra) works fine, but when I swap it out for a AMD Radeon HD 7950 (mac addition) it chimes, fans spin but blank screen. (no boot or anything.)
using a Dell Ultrasharp U2718Q monitor through mini port (not sure if that matters.)

I have the 2 cords for extra power plugged into it working.. what am I missing?

thanks in advance! i’m pulling my hair out. ha.
Maybe try to remove and reinstall the Sapphire 7950HD card. Double check that the two 6-pin to 6-pin cables are tightly connected and plugged in. Try also using a different connection like the Displayport.

A friend of mine encountered a black screen too after the chime. Upon his double checking, one of the power cable was only halfway plugged in. He adjusted the cable so it’s all the way plugged in and this solved his problem.
 

minifridge1138

macrumors 65816
Jun 26, 2010
1,175
197
+1 to double/triple checking that the 6pin power cables are pushed all the way into the motherboard and the graphics card.

I had the same problem the first time I upgraded from my GT-120 to a 5870. With only 1 power cable connected, the machine boots, chimes, the card fan spins up, but there's no video.

It's also possible the 7950 is defective. If you put the GT-120 back in do you get video?
 

MIKX

macrumors 68000
Dec 16, 2004
1,815
689
Japan
+1 to double/triple checking that the 6pin power cables are pushed all the way into the motherboard and the graphics card.

I had the same problem the first time I upgraded from my GT-120 to a 5870. With only 1 power cable connected, the machine boots, chimes, the card fan spins up, but there's no video.

It's also possible the 7950 is defective. If you put the GT-120 back in do you get video?
The 5870 has TWO 6 pin sockets.
Both MUST be powered by Mini 6 pin to 6 pin cables from the cMP backplane Mini 6 pin sockets.

The 7950 also has TWO 6 pin sockets. Both MUST be powered.

Both MUST be powered by Mini 6 pin to 6 pin cables from the cMP backplane Mini 6 pin sockets.


Running NVIDia & AMD cards together is not a good idea as they don't get on well.
 

minifridge1138

macrumors 65816
Jun 26, 2010
1,175
197
To clarify, I didn’t intentionally only hook up 1 cable on the 5870. I simply didn’t have the 2nd cable pressed in all the way.

With 1 cable it looked like the card was plugged in because the fan came on when I powered on the Mac. But there was no video. Then I noticed one cable wasn’t seated properly.

Some versions of OSX/MacOS don’t mind having a mix of Nvidia and AMD cards. I don’t remember if it works in High Sierra. I ran mine for a long time with a GT120 + 5870 without issue.

Check the power cables at the logic board and the gpu. Make sure they’re fully seated.
 
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