[GeoffK]

The wavechange switch should be checked to make sure it opens and closes correctly. S1 S2 short out each aerial coil depending on which waveband is selected. Also look at the tuner to make sure the vanes aren't shorted together and trimmers haven't been tampered with. If the IF and oscillator transformers look intact with no signs of being tampered then voltage checks should be carried out on the osc and IF transistors. Getting noise through shows the detector is working, the detector diode is usually reliable.