[tritwi]

Thank you very much for all of those who posted a reply. Two are the problems with the suggested solutions: The set doesn't turn on without the help of a 60 hz square wave generator hooked to a pin of the digital module.
This 60 hz square wave is generated from the power supply and fed to an input of the module that contains all main processors. I think the ccu need this pulse to switch the system on. The second problem is the vertical frequency cannot be adjusted in any way since it is a digital chassis using not the traditional analogic process but d/a converters that send the signal to digital processors all controlled by the central control unit. The digital signals are then re converted to analog signal to drive the conventional stages (horizontal,vertical,piture tube module,audio power stages etc.). Basically this set is very similar to ours and "on the paper" it could be easily adapted changing the frequency of quarz oscillator . I tried several things but with no luck! I have a multistandard vcr I use to watch my favorite tv show (bewitched) on my televisions (bang&olufsen) but when I hooked it to the Heath/Zenith tv it showed a rolling picture again even if in color.
After several attempts to modify it I also damaged the digital board. Any ideas on how I could get a working one? Zenith never exported tvs to Italy so it's difficult to get parts. Many thanks.