Tandberg TV strange problem

Hi all, another strange problem that I have: Tandberg CTV model 7R63. No IF output from tuner, and the tuner is good, (UV1316-philips) tried another one with no help. What seems weird is, the +33V supply which the tuner requires, is actually fluctating quite much, between 18V and 21V depending on which channel is selected. I also made up a constant +33V supply and fed the tuner , but with no improvment. Since this tuner is I2C bus controlled I begin to think the CPU could be bad, not sending anything to the tuner which is confused. OSD and all other functions is good, also when using the external inputs the set operates good. This speaks for the cpu should be good. Any advice is appreciated, Regards Stefan