[Alex KL-1]

Try to measure the DC voltages of the CRT cathodes. This can indirectly *sometimes* make a clue. If DC reading of the red cathode differs too much from others, something are ocurring. For example, a too low red cat. voltage can make the output stage saturating (on peaks/high luminance). More easy on monitors, since it have less dynamic range than a regular TV since it operates with lower voltages due to larger bandwidth (for not over dissipating).