Hi Phil,
What I would do (and have done in your situation) is start with
another working motherboard... a II+ board would be fine. Make sure
it works. Then take 5-10 parts at a time from your II board --
starting with the ROMs -- and transplant those into the working board
-- testing each time with a power on to be sure that the transplanted
parts are working correctly.
If the test board stops working after a transplant, you'll have to
go back and narrow down further to find which parts aren't working.
If you find that all the ICs are working upon transplant, then
you'll be in more trouble. At that point, I would still suspect a
socket problem on the original board. They often are quite oxidized
and it can take many inserts of a dummy chip and some sprays of a
deoxing agent to get them flowing electrons again.
Only after sockets, would I then start testing each passive
component.. for that you'll need a variety of testers.. BUT.. I've
worked on many of these II's and have not yet encountered a passive
component failure.. so though it happens, it's not the most likely
explanation.