Lisa 2 power supply problems

I have a question. I have been looking for a Lisa for quite some time and I finally found one (Lisa 2 or XL, not quite sure). I brought it home and excitedly plugged it in and ... nothing. No spinning of drives no monitor activity just a small, short hiss that comes from the power supply every time I hit the soft switch. According to sun's pdf repair guide this is perhaps a problem with the power supply (mine is the 1.8 model). Could you perhaps suggest to me (or refer me to source that could) how to check my power supply, or if this is even the right course of action. Have been diddling with this for three days now and have no ideas. I did however take a volt meter to the power supply and noted that while I have black on body of the power supply I only get one five volt reading and nothing else. That comes from the third tooth up and only on one side.