Data General MV8000/9300

Hi, I need a little with my DG Eclipse. It was completely dead to start with because it had a fried front end power supply. The one that hinges out at the back of the machine not the one in the card cage. Luckily my machine came with an expansion card cage with had an exact duplicate power supply. I don't really need the extra 50 or sixty serial ports in that expansion unit so I completely disconnected it and replaced the fried power supply board with the now spare one. When I turned the power on things came to life. Slowly, the message POWER UP TEST COMPLETE is printed on the console but just as that happens, the machine shuts it self down. I have tried powering up with all cards unplugged with the same results. It seems to be the repaired power supply unit dropping out as I can hear it's relays disengaging. I just don't know why. Initially the power, battery and run LED's are on. Then the power and run LED go off while the battery LED starts flashing slowly. The BBU box is not connected as I think this machine was hooked up to an external UPS in it's previous life. One good thing is that when I press the RST switch while the power is still on, I get an Scp-Cli/jp0 prompt and if I am quick I can run a command or two. So my machine is basically alive but only for 30 seconds at a time. I really want to get it going because it has three drives with AOS and Business Basic on it as well as a huge 9 track tape drive. Any help would be greatly appreciated. Thanks in advance, Mike