Well the modulator is a little silver box inside the ST, it's connector is like a phono output on a hi-fi, the end of the aerial is the same as a phono lead, so it might be worth trying another cable, you'd really need another 520ST to replace the modulator, although it looks more like a dodgy connection. These solid cables can be easy to break inside, but chopping the end off your existing cable and fitting a new phono jack onto it should not be too difficult.
Also, there's a little screw beside the aerial socket, there's a hole you should be able to get a small flat head screwdriver into, this changes the frequency that the ST's modulator transmits at - try adjusting this. IIRC the ST interfeered with the bandwidth of certain types of video recorder, adjusting the frequency might fix it but you will need to re-tune your TV.
EBay would be a good source for monitors, I've no idea what sort of prices they go for though. Do you know anyone with an old AmstradCPC monitor though? - they can be madified to work on ST's by rewiring then to suit the ST's monitor port.
Van-B
It's c**p being the only coder in the village.
