I had the exact same issue this week working on an 0D whipplecharged app. I have a couple romulators from xtronics. To check those I read the emulator using my eprom programmer to verify the file. The problem ended up being the moates zif adaptor. Not knocking moates at all as zif adaptors are notorious fail points when using machine pins whereas the soft pins of a chip usually work. Cold solders are always a problem with anything so definately re-silver solder all points, just one note with a zif socket, always slide the connection back and forth while slowly closing the zif socket so it "digs" into the pins for better conductivity.
-Carl