RCA 8TS30 Negative Image

[Chris K]

Working on my first KCS 20J-1 chassis. Replaced all electrolytic and wax caps and put a pattern generator on the set. I get a clear, focused, somewhat stable negative image. If I manipulate the focus coil, loosen the wing nuts to move it and fool around with it, occasionally it'll snap into the right B&W configuration for a second but then reverts. Any idea where I should start looking? I have not changed any resistors yet nor have I tested any.