Two External Displays in Yosemite

[SeberrY]

Hi everybody...

I just got a brand new 21.5" iMac, and I connected two external displays through Mini DVI --> HDMI cables. These two displays are each connected to the two Thunderbolt ports on the iMac.

When I started the computer for the first time and set everything up, all three monitors (including the iMac's internal one) worked fine, but when I upgraded to Yosemite, I can only get it to recognize one external display at a time (whichever was plugged in first).

Anyone have experience with this? I'm making a mountain lion USB as we speak to downgrade... It's a shame!

I've tried restarting, resetting SMC, and resetting the PRAM.

 

[Kyle-K]

Anyone have experience with this? I'm making a mountain lion USB as we speak to downgrade... It's a shame!

You're running a non-released version of "Yosemite" So who knows how did you go reverting? Did everything work again?

Requested a move to the "OS X Yosemite" Section of the board as its most likely better suited in there and I highly doubt it's a hardware issue.

Notice: I wish people would use disk utility to add another partition and install Beta OSs in there.

 

[SeberrY]

Reverting went fine, and yes my two external displays work without a hitch. I realize it's beta software, so I hold no ill-feelings towards Apple... I'm just surprised this hasn't been fixed this late in the development of Yosemite. Now I'm looking forward to the public release.
Cheers.

 

[jmj8778]

Same

Just chiming in saying I've had the exact same experience. My dual monitors worked perfectly on Yosemite for 1.5 months and all of a sudden it's only whichever is plugged in first.

Upgrading to developer preview 7 to see if that fixes things, already ran a number of fixes that are customary for mavericks machines with this issue to no avail.

 

[SeberrY]

I've had the exact same experience.

Does the latest version (the GM Candidate) fix the issue for you?

 

[mmomega]

Hi everybody...

I just got a brand new 21.5" iMac, and I connected two external displays through Mini DVI --> HDMI cables. These two displays are each connected to the two Thunderbolt ports on the iMac.

When I started the computer for the first time and set everything up, all three monitors (including the iMac's internal one) worked fine, but when I upgraded to Yosemite, I can only get it to recognize one external display at a time (whichever was plugged in first).

Anyone have experience with this? I'm making a mountain lion USB as we speak to downgrade... It's a shame!

I've tried restarting, resetting SMC, and resetting the PRAM.

I went from Mavericks to Yosemite DP1 with my iMac with 2 external displays and they have been working flawlessly since I connected them, wish I could help you. I've gone through every DP and never lost either display.

Just on a 27" iMac with dual 27" Monitors connected MiniDisplay to HDMI.

 

[jmj8778]

Does the latest version (the GM Candidate) fix the issue for you?

I ended up reverting due to this issue. I believe the last DP I was on was 7, but it may have been 8, and it was still not working.

You?