Mini displayport issue on late 2009 imac
I have a late 2009 27" imac. The hard drive died so I replaced it with a SSD and installed MacOS High Sierra. Everything works perfectly.
I have been trying to use the old imac as an extended display for a newer imac (late 2013) using the thunderbolt port on the newer mac connected with an apple thunderbolt cable to the mini Displayport of the older imac in target display mode.
Neither mac can find the other as an extended display. When I run a system report of the older imac I can see the usb and firewire ports listed under hardware but not the mini displayport.
Do I need a driver for the mini displayport? should I try a MDP cable instead of thunderbolt? If anyone has any suggestions I'f be grateful for your assistance.