[julie_m]

Some TV manufacturers cheaped out on the SCART connectors, and relied only on the soldered connections to the motherboard to support the socket, instead of riveting it to the board and/or screwing it to the outer case of the set. It did not help that, by dint of the form of the set not making it easy to turn around, one was often having to work by feel just to insert or remove the SCART plug.

In the event of loss of sound in one speaker, or weird colour problems such as complete loss of blue, the advice was always the same: Re-solder all the pins of the SCART connector. Moving the plug in the socket will not always restore the broken connection. Once I overcame my phobia of TV sets, I fixed a few with this simple method.

The SCART connector is designed to be able to accept a full composite colour video signal with blanking and sync (CVBS), or it can accept an RGB signal and use the CVBS input only for timing. If the earth return for the red signal has become disconnected, that could cause your problem. The BBC Micro's RGB output is suitable for connecting to a SCART input with just a few resistors and two diodes; a TV repairer could fit a suitable DIN socket, but it and the SCART socket should not both be connected at the same time -- permanent damage is very unlikely, but weird visual effects are practically certain!