The easy way to check your wiring is as follows. You have two transmit wires and two receiver wires. With a ohm meter the transmit wires have the lower resistance. The receiver has the higher. Connect transmit to transmit and receiver to receiver on the board. To check if wiring is correct do the following. Turn detector on and in all metal/ pin point you should have a threshold tone. If you have no tone the receiver wires are reversed. With the detector on and in all metal/pinpoint pass an iron object pass the coil, if it nulls the transmit wires are reversed. I have seen two different NEL ATTACK coils. One white with a black cable and a black coil with blue cable. The white coil was listed as water resistant and the black with blue cable labeled water proof. Not sure if there is a difference. If you look very closely to the wires you will find them numbered 1 thru 4. At a glance they appear to be all black but they are faintly numbered.
If the coil responds to the test as listed above it is not a wiring issue. EMI and RFI a loose coil cable, a dirty coil cover ( remove cover and clean ) and water in the coil will give the symptoms you describe. You did not say if the coil is hard wired or you are using some type of water proof connector as the latter could be the issue also. Hope this lengthy response helps before you send the machine off. Another note is people be leave that the sensitivity knob controls the depth of the Excal and this is not always the case. The trick is to make your machine run smooth even if you are running at three o'clock. The depth will still be there. Bury a target and test. Good luck.
