HP2100 help requested

One of my 2100's has developed a problem. It was working fine for some time, but was only powered up occasionally. The problem started when I ran some burn-in diags over several days. The machine started acting funny, and when I powered it off and back on, there's no front panel display at all - no lights. However, all the fans come up, one of the internal boards that has an on-board led is lit, and I checked all the outputs of the power supply and they're just peachy. I moved every single card (including the front panel) from the bad system to another system and it then runs fine so I know it's not any cards. I suspect the power supply, but as I said all the outputs appear good. Gawd I hope nothing happened to that wire-wrap backplane. Can anyone offer some advice? I'm starting to pour over the schematics on the power supply - wondering if something is amis with the poweron or powergood signal perhaps but I don't know much about it. Any tips most appreciated! Jay West