Hi again,

Thank you for your useful comments which were all duly
noted. However I have been able to clear the problem after
a deal of head-scratching. It became likely that the leak
was between supply lines and not simply to ground when the
PA cooling fan started-up on receive.

The fault turned out to be a s/c between the tops of two
zero-ohm resistors (links) on the IF board just a little
north-east of the speaker plug. As I was the last person to
plug and unplug that particular lead, I guess that I must
be the guilty party.


Thanks again - Joe