Grab a desoldering gun, pull the trigger and wave it around the face of the CRT. This will reveal any CRT damage that could have occured, it will also degauss the CRT as well.

Trinitron tubes are VERY vulnerable to physical vibrations and too strong of magnetic fields. and can change the purity of the CRT permanently. I had this issue with older trinitrons before.

So use the soldering gun degauss technique just to rule out the CRT ;-) then maybe attack the degaussing circuitry. Its 1 of 2 things in that case, either the thermistor, or the cut-in relay.