STFM LOW MED screen colour picture scrambled

[Chandler]

hi all

 

i have a 520STFM totally standard that works OK in high res black and white mode - good pic with sound BUT

 

in LOW and MEDIUM res on a colour monitor (and TV) i get the below scrambled screen

 

i can hear sound on the monitor but not very good on the TV

 

i have changed the video shifter and small MC 1337 ic chip behind the TV modulator oh and yes the monitor is fine!

 

my STFM test cart says the video shifter, MPF and timing are ok

 

can anyone advise what to look at?

 

thanks