I have a power supply for an lcd monitor that only works after being
heated. It will work fine so long as the monitor is kept on. After
cooling down, it's difficult to get started again. Occasionally it
will start with being unplugged and replugged, but usually it requires
heating. Eight minutes in the oven at 300F works consistently (wrapped
in a thin towel).

In the past I've had reasonable luck with this kind of failure just by
starting with the largest cap and pulling them until I find one that's
obviously leaking or shorted (testing with an ohm meter). This time,
however, the broken part isn't obvious to me.

I thought that perhaps I could isolate it by heating or cooling parts
until the unit started or stopped working. I tried using a soldering
iron for heating, and canned air for cooling, but neither had a clear
effect. Is there any other technique I might use for heating or
cooling individual parts?