Can anyone help me with diagnosing an electrical problem somewhere in my system?

A couple weeks ago I smelled that odor you associate with electrical fires. After the smell dissipated I turn the power amp on by itself and decided to start there and go upstream. After ten minutes I smelled that odor again so I dropped it off to be fixed and swapped in a spare power amp I have as a backup. Now I smell the same thing and this after playing it for hours without trouble. Does anyone have a routine for identifying the source of such a problem? Thanks in advance for any help you can give.