The problem with my 55fx20b turned out to be a little three terminal voltage regulator in the main switching power supply. This thing looks like a TO-220 case power transistor. The referance number is I904 and it is tied to the B+115volt line that feeds the horizontal output stage. The actual part number is SE115. They can be obtained from your local dealer for less than $10.
Godfrey Leggett, December 2010