Dead Sega SC3000H

Hi everyone, I've been working on a Sega SC3000H: http://www.old-computers.com/museum/computer.asp?c=206 It seems to have the common problems that afflict these. Firstly, the 7805 regulator was dead. I pulled it and gave the machine 5V from an external supply, and it ran fine - apart from what looked like a horrible RAM fault. I can see it's trying to do something sensible, but the display is corrupt. So, I tried the next test for obvious RAM failure - are any of the RAM ICs getting unusually hot? Seven were barely warm, but one is almost too hot to touch. Now, this is annoying because I don't want to spend a great deal of cash on this machine, but I'd really like to get it going. I have two questions: - Am I jumping to conclusions re the faulty RAM? The ICs aren't socketed, can anyone suggest any worthwhile tests? - Does anyone know of somewhere I can get a MCM4517 P15 or equivalent, nice and cheap? One problem - I'm in New Zealand. I'm a software guy really, but I do enjoy getting stuck into the hardware from time to time! Mike