[Biggles]

Damo, thinking about your other deaf set, and looking at the kind of things handportables are subject to, it may be worth checking the crystal filter as this could have been damaged in a drop. Linking it out may be a quick yes/no check although not ideal. You may have a bad capacitor (tantalum bead? can't remember) somewhere. It may be a bit off frequency too, which wouldn't help, if you have some way of checking this. We used to zero beat the local oscillator by injecting a 10.7MHz low level unmodulated signal into the IF stages and also an on channel carrier from an accurate signal generator (or the transmitter) and tweaking the receiver local oscillator for zero beat i.e. lowest tone heard in speaker. Since the advent of synthesisers this procedure has become obsolete, as you just need to adjust the transmit frequency to the correct value and the receiver is bang on too.
Alan.