Mid-2012 13" Macbook Pro freezes when attaching an external monitor

Hi everyone, I recently purchased a used, mid-2012 13" Macbook Pro. First thing I did was reformat the drive and re-install Mountain Lion (10.8.2). The machine has all the latest updates (as of today), but I'm running into an odd and very frustrating problem: Whenever I plug my external monitor into my Macbook, it almost always freezes. The external monitor receives no signal from the Macbook, and the Macbook monitor will turn either white, blue, or simply show the normal background image. Sometimes I can still move the mouse cursor, but nothing is clickable.

Usually, I can close the lid, unplug the external monitor, open the lid, and everything will be fine until I try to plug the external monitor into the Macbook again. Sometimes, however, the Macbook completely locks up, and the only way to get it working again is a hard shut-down and reboot. After going through this nauseatingly frustrating process for a few minutes, the display will suddenly start working properly. There seems to be no rhyme or reason as to why it works when it does. Sometimes it takes only two minutes, sometimes it takes ten. It seems to be random.

My external monitor is an HP LE2201w. It is my work monitor, and is VGA-only. I have a VGA-to-Thunderbolt cord/adapter from the monitor to the Thunderbolt port on the Macbook. Looking in my System Log, I see a lot of messages like the following:


Here's a screenshot of part of my System Log from when I was recently trying to get the display to work: https://dl.dropbox.com/u/583606/tech_stuff/display-log-2012-12-28.png

I tried a co-worker's display (using a different cable) and had the same problem. We unplugged and re-plugged the display several times; about half the time, the Macbook froze up until we disconnected the external monitor. The other half of the time, it worked fine. It appears to be completely intermittent.

I also ran an Apple Hardware Test, both simple and thorough, and it did not find any problems with my hardware. Any help deciphering the problem would be greatly appreciated.

I'm going to guess here and say it's the cable(s) you're using. Those messages and the way it's acting appears to be an incompatibility. You should be able to use a Mini Display Port adapter to VGA and then a straight VGA cable to the monitor rather than fool with the Thunderbolt adapter. Give that a try and let us know. (The Thunderbolt port is backwards compatible with MDP.)

Thanks for the reply; I will definitely get my hands on another adapter to see if that's the problem. It's a VGA-to-Thunderbolt cable and adapter in one--it's very simple, yet I agree with you that it could very well be the cable that's causing the problem, as my co-worker has the same type of cable as well. I'll look into it for sure.

hi,
I'm experiencing the same pb, did you try to replace the adapter ? did it solve the pb ?

my adapter is a belkin TB to VGA (mbp mid 2012)