An update to this thread.
Outcast has kindly forwarded the surplus autostar controllers that he got off spiezzy to me after fixing his hand controller.
There were two different boards inside the controllers, one with a wider ribbon cable to the screen, and two with a narrower ribbon cable. One of the handboxes with the narrow ribbon cable partially works (screen starts off normal brightness but then becomes very bright and needs to be read at an angle.
My broken 497 was of the type that had a broader cable, so all I could do was switch out the broken screen on the one 497 with my screen and vioala, it worked! I had tried cleaning my cable as mentioned on this thread (and other forums) but it appears as though my problem had to do with the board, so I got lucky by having two different problems across the two controllers
Many thanks to spiezzy and outcast, and if anyone needs some controllers to play around with for a repair there are now two in the pile that remain non-working, and one partially working one.