If tweaking what Mod said doesn't work, this can also be caused by having the horizontal pot too far one way and the pot on the PCB (one controls up/down and the other controls left/right IIRC) too far the same way. A double whammy if you will.
You need to find the happy medium between both.
Pulled chassis out and reflowed solder and repaired some traces. Look like a cap
kit was down on it already, they just never checked for cold solder joints.
Looks great now....