Welcome here!
With RF cable your machine working?
It is a common motherboard failure when the internal 12V circuit broken. It is for the video circuits, and also it is the 12V output on monitor connector for the Scart switch signal.
Then first check 12V are present on the Scart plug?
Connector pinout and the commonly used Scart cable wiring at
bottom of this page.I bought cables from Spain and it is worked for me. I will check which resistors used.
It is a more than 30 years experience: some TVs need to play with the resistors values.