Loose AV connection on Master System

I have what appears to be a loose AV connection on my MS; it produces a scrambled picture unless I wiggle around the cable at the connection, but wiggling only provides a temporary fix as it soon returns to looking scrambled. I know it is not the cable as it works perfectly with my other MS.

Any quick and simple fixes for this?

The DIN jack just needs to have its solder joints reflowed, that's all. Most SMSes have a cheap PCB without plated holes on the top side, so the DIN jack eventually cracks its solder joints when it's been pushed and pulled on too much.