I just picked up a used Tejon and I'm having a little trouble getting a reliable ground balance on it. Is it a slow retune machine in all metal? Seems like I'm having trouble getting the threshold tone to stay sounding after lowering the coil to the ground, even though I'm turning the gb knob. I'm wondering if something isn't loose, because all I have to do is tap the housing to get the threshold to sound when I have the coil up. I sent the unit into Tesoro and they checked it out, but they shipped it back via UPS and I've had bad experiences with UPS banging up equipment.