DEC Professional 350 Fault

The DEC Pro 350 I got came without a monitor, cable or keyboard. When I power it up the diagnostic LEDs on the back all come on. The docs I have suggest this means a system board error. However, I am not sure if this is because there is no monitor or keyboard attached. Might this behaviour be expected if I don't have anything connected to the video connector? I tried connecting a terminal to the serial port just in case something happened there, but I don't see anything. Does the Pro 350 use the serial port as any kind of console port by any chance? I suspect not. I am trying to identify what cable I need. I think it is a BCC02, but if it is a colour machine it would be a BCC17, but I don't know how to tell if this is a colour machine or not. There also seems to be a BCC03 cable used on Rainbows, anyone know if that would work? Regards Rob