iMac mid-2010/10.10.3 -> Stopped detecting external display

[Tigerman82]

I have a 21.5" mid-2010 iMac with OS X Yosemite 10.10.3. For years now I've had my Sony-TV connected to the iMac via an HDMI-cable and a HDMI-to-Mini Displayport -adaptor. I've had zero problems with this setup. However, last night I wanted to watch a movie from my iMac via the Sony-TV but the screen was all black. I then went to my iMac and discovered that it had stopped detecting the Sony-TV. I did the following procedures:

• Switched all devices off and reconnected all the cables
• Checked that the Sony-TV's HDMI slot was working and that the HDMI-cable was working (connected it to a Windows-PC)
• Ran the Onyx Automation procedure
• Did SMC and PRAM resets
• Booted the iMac from a clone drive (taken when the HDMI-connection between the Sony and the iMac was working)

Alas, nothing helped. I have read that sometimes, after OS X updates, people have trouble with their external displays but this happened well after the 10.10.3 update and since the update I had used the Sony-TV with the iMac without a single problem.

Do you have any suggestions?

 

[oldmac1988]

Not yet? And, shame on you, MacRumors.

Over the years, I have learned never ever install a software update for a month. Then, I search here and do general searches online for reviews for the software update. So far, the latest news I can find suggests to me I should wait a bit longer. I will never ever endure the weeks of pain and suffering of Nov to mid-December of 2014.

And, shame on you, MacRumors. I do rely upon your voices; you are important to me. Today smack dab in the middle of the ads at the top of the page is one for Mackeeper, another nightmare no one else should have to endure. Is it anything for money?

Also, this week I purchased an application at iTunes which I thought was a solid Apple-backed store. NO! First, anyone can offer their application and the store will take a look and decide whether or not to offer it, but it does not mean that it really will be compatible with my computer, even if the ad says it is. Reviews I read must have been written by investors and creators of the application. Ok, though. Of course, iTunes credited my account and I learned something. Deal.

 

[Tigerman82]

I have now found out that the reason my iMac stopped detecting my Sony LCD-TV connected via HDMI was because the 10.10.3 update doesn't fully support (or breaks) Macs (I don't know if this applies only to older Macs, certain models etc.) with ATI video cards. So either Apple screwed up or they don't want to optimize updated to older ATI video cards.

Those in similar situation will have to either go back to 10.10.2 via a backup (which I don't have) or a clean install (Yosemite installer plus 10.10.2 combo update) OR wait for an official or an unofficial fix. For now, I will choose the latter.