If it's got a solid +5V, my next trick is to use a logic probe and touch a RAS pin on one of the RAM modules.
Generally if the system is generating this signal, the basics are working, and chances are the failure is in the first 16KB or so of memory [which is when I write a Supersoft/Landmark Diagnostics ROM and pop that in].

That case certainly got around, similar thing used on Acer 500 [from memory] and my ITT Xtra.