I have an A4000T which has an extreme manifestation of this problem.
I have to keep the power off for up to two minutes in order to prevent the Guru from returning after a bad crash. Needless to say it's quite an inconvenience.
I have tried several different CPU cards. No difference.
Power supply has been checked for both voltage and noise. No problem there. Reset has also been checked. It pulls low cleanly for at least 500ms and returns to a full 5V.
Even more weirdly, I can sometimes cause this problem by adding or removing a Zorro card, and if I do this and turn the machine back on within two minutes I get no boot and a blinking power LED. Wait for more than two minutes and the machine then powers up perfectly!
It even remembers the kind of crash too. If I had a red software failure message, that's what I get again if I power up too soon. Likewise if it's a black screen and blinking LED, or simply no boot at all, even though the power LED changes brightness.
