Hi David -
Finally returned from travels and trying to set up the printer / scanner with all due patience:
(1) Operating system is (was) MAC 10.7.5 - just to note - it's a bit out of date
(2) I reset the printing system in MAC Systems Pref - and found the Printer, and added it. Unfortunately it adds only as a printer - not recognised as a scanner. So the Sys Pref screen I see when I use my Mac (version 10.12.6) is as follows
Having reset and installed the Office Jet 7740, the screen I see on my wife's Mac is as follows:
As you can see - no scanner option.
I then went to the software and driver downloads page as suggested. I'd actually done this before but deleted all the previous downloads before starting again to ensure I had a clean start. The only driver available on this page for this machine is ReadIris Pro 14 for HP, so I downloaded that again and installed the software.
I launched ReadIris, and clicked on the Scan Icon - and recieved the error message "Unable to Open the Twain data Source"
I also tried HP Scan. This was already installed since the previous printer was an HP ENVY 120. I tried using this, employing the dropmdown menu to "Browse Scanners". Unfortunately it does not see the HP 7740.
I tried scanning from the 7740 to the computer via the control screen on the printer, but it cannot see the computer
I gave up on this trail of solutions and installed Mac OS Sierra (10.12.6)
I then went to Sys Pref, deleted all printers and reset the printing system. That worked. Here's the screen from the second Mac now:
I can now access scanning from Sys Pref and use HP Easy Scan, and Read Iris as well - all functional.
I think maybe HP should just alert folks that some printers / scanners wil not work unless you have the latest OS.
Thanks -
Peter