Is it the Power Supply or the unit?? Lexicon DC1

I have a lexicon DC1 ( a high end digital surround sound processor) that wouldn't power up so I opened it up and found the oem power supply a NAN40-7610 was not outputting 5V The supply which is a 100khz switcher would not start and the 5V went to about 2V and collapsed . It worked fine without a load Trying to determine if it was the unit or the PS I "helped" the 5V with a diode isolated external power supply and the unit came up and ran fine. If I let it warm up I could turn off the AC then back on within a few minute and it came back up. If I removed the AC for more than a few minutes it wouldn't start until I jump started it again. I loaded the PS with a 3Amp resistive load (which is its rating) and it comes up fine When I put a scope on the supply I find that the chopper input to the transformer oscillates for a few milliseconds that dies then restarts and collapses over and over. After I "jump start" it the chopper looks fine Not wanting to make a career of fixing this power supply which I can buy for $50 I'd be interested in anyone's opinion as to whether its the PS or some condition on the board that is preventing it from starting and if so what should I look for. Also any likely candidates on the PS would be interesting Unfortunately I don't have a schematic of either the DC1 or the PS Thanks in advance bob