I have a iMac (27-inch, Mid 2011) about 9 years old. After upgrading to Sierra, everything seemed to be working well and considerably faster that my older operating system ? and then, my display screen starting going black after a half hour, and then progressively shorter intervals. The computer seems to be working fine ? the screen just goes black. I thought it must be the memory card but when I brought my machine to the Apple Store, where they ran a full diagnostic ? the technician said everything was fine but there was something wrong with the display function on my monitor. Since the machine is more than 5 years old - they will not service it.
I was wondering if hooking up another monitor to it will work. Not sure how to do this. The computer is not worth spending a lot of money on, but I thought this solution was worth a try and was wondering if anyone else encountered the same issues. The SD card reader no longer works, but really the rest of it aside from the display seems to be in perfect working order.
Many thanks
Buy one of these adaptors to use an external monitor.
https://www.amazon.ca/s/?ie=UTF8&keywords=thunderbolt+to+vga+adaptor&tag=googcana-20&index=aps&hvadid=208445126088&hvpos=1t1&hvnetw=g&hvrand=3594744729822014304&hvpone=&hvptwo=&hvqmt=b&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9000666&hvtargid=kwd-304282895410&ref=pd_sl_6qajk1kisv_b