mitchW said:

Reset PRAM and check PRAM battery. Also there might be caps inside the PSU going bad, causing erratic power-on/off behavior, but they were not problematic as, for example G5 iMacs.

Click to expand...

Yep, this was one problem. I had never checked the battery since I bought this about three years ago, because it looked new. But the battery was in *backwards*! I'm lucky it didn't blow up or something. It didn't solve the problem I was posting about, but thanks for getting me to check something which could have caused a worse problem.

Hrududu said:

Congrats, your power supply is failing.  I'm doing some looking at repairing the Samsung one in my dual 1.25 as we speak.  It used to come on using the button on an ADC display, but i transported it and now it won't boot at all anymore.  My dual 1.42 will still work most of the time, but I have to leave it plugged in all the time.

Click to expand...

Failing to do what, exactly? Mine is the opposite of your 1.42 symptom, I can't leave it plugged in. I suppose I should do a more general search about MDD PSU repair. Feel free to link any you care to recommend.