Mini displayport curiosity

jhall1jax

macrumors newbie
Original poster
Sep 2, 2006
22
5
Just traded my 2012 rMPB with my buddy's 2010 5,1 Mac Pro 12x2.66 with the 5870 card. He's used it for years with the old Apple 30" monitor which used a (dual-link) DVI. He's never used the minidisplay ports.

I initially had the Mac Pro hooked up to a cheapo 1920x1080 monitor via DVI for a few days. I have 2 2560x1440 monitor that have displayport connectors. Using two mini displayport to displayport cables, I plugged them in and they work great at the native resolution. I disconnect the DVI monitor and put it away.

Everything was fine until I slept the Mac Pro, then woke it the next day - I hear it click on and the fans spin up, but no video. I rebooted, no boot. I disconnected one monitor, and plugged the other in to the DVI port (instead of the DP port) - still no boot.

The only way I could get it to boot was to get out the first 1920x1080 monitor I used via DVI - then it boots fine. After more testing, it looks like I cannot get it to wake when ANY monitor is plugged into one of the mini DP ports.

I swapped out the motherboard CMOS/NVRAM battery (and thereby reseated the 5870), reset SMC and PRAM. No effect.

Anyone else have this issue? Very weird.

On another note, I heard that the "stock" Apple 5870 uses a single 6-pin power connector. Mine is a double 6-pin, and isn't branded Apple anywhere. I'm assuming this is the Apple-supplied 5870 but I'm not 100% sure.

Jason
 

ActionableMango

macrumors G3
Sep 21, 2010
9,514
6,772
Non-compliant DP and mDP cables are fairly common and can pass through 3.3v on pin 20 which can either damage equipment or prevent a computer from POSTing. This matches your experience perfectly, so I suspect the cables.

The Apple 5870 uses two 6-pin connectors. Maybe you are thinking of the Apple 5770, which uses one.
 
Last edited:

jhall1jax

macrumors newbie
Original poster
Sep 2, 2006
22
5
Interesting and thanks for the reply - the ones I bought appear to be appropriate cables (they are v1.2 cables):

https://www.amazon.com/gp/product/B00C7RJQPY/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

Same behavior when using the DVI connection to one monitor, along with a good-quality active miniDP-to-HDMI converter feeding an HDMI connector to another monitor. The computer just doesn't seem to like anything plugged into a miniDP port when booting or waking. I've been building PCs and using Macs since the early 90's; haven't quite run across this issue before.

Edit: spelling
 

ActionableMango

macrumors G3
Sep 21, 2010
9,514
6,772
Interesting and thanks for the reply - the ones I bought appear to be appropriate cables (they are v1.2 cables):

https://www.amazon.com/gp/product/B00C7RJQPY/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1
There are two reviewers who specifically say that it passes through power on pin 20, which is exactly the problem I was concerned about. If you want to read more about this:
https://hardforum.com/threads/displayport-cables-must-not-use-pin-20-warning.1803684/
 

jhall1jax

macrumors newbie
Original poster
Sep 2, 2006
22
5
There are two reviewers who specifically say that it passes through power on pin 20, which is exactly the problem I was concerned about. If you want to read more about this:
https://hardforum.com/threads/displayport-cables-must-not-use-pin-20-warning.1803684/
Wow, great catch! Thank you for checking on that. I'll see if I can return those two cables and get cables (like the below) that are confirmed pin 20 disconnect.

https://www.amazon.com/Accell-B143B...&sr=8-1&keywords=accell+mini+displayport&th=1
 

ActionableMango

macrumors G3
Sep 21, 2010
9,514
6,772
What worries me is that you are seeing the same problem with the MDP-HDMI adapter. So either the out of spec cables are not the problem, or the damage is already done.
 

jhall1jax

macrumors newbie
Original poster
Sep 2, 2006
22
5
What worries me is that you are seeing the same problem with the MDP-HDMI adapter. So either the out of spec cables are not the problem, or the damage is already done.
I'll report back when the "in-compliance" cables arrive tomorrow.
 
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