My 2011 iMac 21 inch died a couple of weeks ago. The hardware is still working but I tried another screen and couldn't get it to work so I'm guessing that the motherboard has gone. I connected it to my 2019 iMac via the appropriate cable and tried target mode but couldn't get a disk image on my new Mac. I've stripped it down and removed the HD and with the 2011 iMac it comes with a pcb, so I can't use a conventional carcass to run it externally. How can I retrieve the data?