On Sunday 04 May 2008 23:27, Al wrote:

OK, I'll do the check with the 'scope. And the time of the start of the
tearing does vary with the interval between startups; something must be
temperature sensitive.

That does not rule out capacitor based problems. I've repaired several
mainboards which had leaky capacitors, which worked fine as soon as they were
warm. It's the opposite to what you're experiencing, but it illustrates that
caps are temperature senstive.