Jake Joseph wrote:

Well, you are right about the 5V - it gets its reference off of the 5V
- shoots this through a TL431 regulator.

I'm guessing that either the switcher has gone bad or the optoisolator
xsistor has gone bad...any good way to diagnose?

Diode tester function on a multimeter will help you check the switching
transistor in-circuit. You can do the same with the optoisolator. You
can't find all possible failures in-circuit but you can find some of them.
Worst case you pull it out, test the switching transtor with the Hfe function
on your multimeter and swap out the optoisolator (being sure to put a socket
on the optoisolator because this will happen again someday).

Switching supplies are no fun to fix, because you can't get them running
to do diagnosis. A storage scope can help a lot.

Don't forget the kickstart circuit either, which is a source of failure in
a lot of switching supplies.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."