mini display port to DVI not working?

Hi, I seem the have the same thing here. I even had the PowerBook 2012 checked out at the Apple Store. Has this happen prior to or after installing El Capitaine? Mine worked fine till I upgraded. Are you using an Apple or other brand? Myself I am or rather was using a Dymex just fine for many months before El Capitaine. Could this be software related? Oh by the way I have 2 Thunderbolt ports they told me and not a mini display port.

My problem was/is with my 2011 MacBook Pro. To answer your question.... this was happening when I was using OS 10.7 something not El Capitan. By chance I found out how to avoid ruining my DVI connector other than disconnecting it when I was not going to use it. It turns out that when I left it connected and the hard drive would power down (computer sleep) based on the energy save settings, then the DVI would never work again. The Apple repair folks could never get it to fail because they never let the computer automatically "sleep'. I consequently set my preferences so that my Mac would never go automatically into "computer sleep" and have not had the problem again. However I just upgraded to El Capitan and have not tried it again for fear of losing another DVI dongle. I suggest you might try the "no sleep" setting in preferences just to see if that works for some strange reason. BTW... so far I am not impressed with El Capitan.... it slowed EVERYTHING down and some operations take minutes to function. Hope Apple fixes it soon.

THanks for the reply, I went to the Applestore and got it checked out. It happens to be the dongle. the wire was crapping out. If I push the wire into the plug it works again until I pull it again. I will eventually buy a new one. I hope you find a solution too.

I am having a different problem with my Mini Display Port. I had no problems getting my DVI to connect to an analog TV. I used to connect successfully and watch on the screen fine with no problems. Just a few weeks ago I connected my MacBook Pro again as I usually have before and it will not work with my TV display as before. When I plug it into the TV with the mini display DVI, it Cycles through multiple screen sizes without stopping. It constantly switches between various scaled screen sizes. It flickers between the color bars and my computer screen.I suspect that my port is going bad. Does anyone out there have a similar problem or know what might be going on? Any advice would help me. Thanks.

Hi there,

May be this will help people.
I had the same trouble with my Mac Mini (late 2014). I tried to plug my "old" screen in DVI with a MiniDisplayPort adapter. The screen "said" NO SIGNAL.

I broke my mind for a couple of hours and I had an illumination. As you can see here there is many different DVI connector. My screen and the DVI Adapter have a DVI-D Dual-Link connector but my screen cable was a DVI-D Single-Link. I just bought a DVI-D Dual-Link and it works well !

Bye !
J

I can confirm that a SINGLE link DVI-D cable did the trick. They say it should be backwards compatible, but appearantly it isn't.