Hi Smokey44:
One of the Sony parts distributors, Encompass Parts, sells two cable assemblies for the EVI-310, and both are under-$20 USD, each:
P/N: J-6082-293-A Descr.: CABLE, VIDEO OUT Price: $10.64 USD
[link: http://www.encompassparts.com/item/2319976/Sony/J-6082-293-A/Cable,_Video_Out ]
P/N: J-6082-291-A Descr.: EXTENSION CABLE,REMOTE CONTROL Price: $17.62 USD
[link: http://www.encompassparts.com/item/1456804/Sony/J-6082-291-A/Extension_Cable,remote_Co ]
Sadly, Encompass' site has no photos of either, to verify connectors, so my gut feeling would be to go with the first one ("J-6082-293-A Cable, Video Out"), unless it's just an internal jumper.
You might check Sony's main ProVideo website for "Parts & Accessories" for the equivalent of a replacement Power/Video Out cable with connector.
I've seen the Service Manual for sale on eBay (search using the EVI-310 model #). That would have the pin-out diagram for power & signals. (You might also get lucky with one of the PDF manuals hosting sites like Retrevo or ManualOwl.)
hope this helps,
--Dennis C.
