Blue CRT Flashes Off
 

I have a 1988 Magnavox RPTV; PTV 325 chassis.. Approximately 1/2 minute
after turning on, the blue crt(color) turns off for 1 to 3 seconds; this
may repeat 2-3 times, always within the first 1-2 minutes of turning the TV
on. No problems afterwards. Tapping on the neck of the blue crt, the
blue crt board, or any of the other boards did not cause any color change; I
assume this rules out bad connections.

Any ideas/explanations of what I should look at next would be appreciated.

Emilio