"With our old Seiko tuner we always get the same reading whether we use the Matrix pickup or not but the tuner needs to be replaced because the input connector is dying" - might be worth trying to put a new socket in it or failing that solder in a lead with an inline socket on it. I assume it's a standard 1/4" jack ?

McGrath: It's probably because your tuner has it's pride and refuses to have anything to do with Derek Brown's banjo !