More revelations on coil connectors

A couple of years ago I wrote an article on coil connectors and why is was important to keep then clean. Fine particles of dust can increase the resistance of the metal to metal contacts and this can end up making a noisey detector. This article is based on some new discoveries that came to light when a customers GPX4500 detector that was excessively noisey. The first thing to do was to get the coil connector cleaned up with contact cleaner and some cotton buds, after cleaning the detector was a little better but just touching the coil cable near the plug sent the detector into a high pitched scream that took a few seconds to settle down. I then removed the cool connector end plate on the detector and checked that all the coil connector wires were soldered correctly and they were. I connected the detector up to a load that emulates a coil and tested the input circuitry to observe the noise component in the detectors receiver. I multiplied the receiver signal by ten times so i could get some fine resolution to what i was looking at and recorded the measurements.  I then connected a reference GPX4500 to the equipment and could easily see the noise was much lower. I then used a shorted coil connector to make an electrical short and connected a very precise ohm meter that can measure down to 0.001 of an ohm, the noisey detector was showing five times the resistance on the coil plug to socket than the reference detector. I then used a magnifier and a bright light to observe the pins on the noisey detector and I noticed that all the gold coating was gone, it even looked like the Nickel plating was pitted away and the connection was going onto the steel pins directly.  Could this be causing all the noise?  I replaced the coil connector on the GPX4500 and it is not an easy job as the nut threads have had something like locktite applied to them to stop the nut becoming loose. After fitting the new coil connector the problem totally went away.  It seems that changing coils many times starts to wear away the relatively soft gold coating and this can happen on both the coils and detector connector. I would never thought that this would cause a problem of this magnitude but when you think that the very small nanovolt signal from the coil is amplified hundreds of times the resistance change in the metal to metal contacts is also raised by that amount.

Losses in the metal to metal contact if not perfect can cause signal loss and cost you nuggets. If you feel inclined to change the coil connectors yourself be careful as many aftermarket coil plugs and sockets are not gold plated and also the pins seem to be thinner and will not make good contact. If you really want to do it yourself I have the proper gold plated plugs and sockets available. On further thought about this problem I have come up with a system that greatly reduces the wear on the coil and connector by using a special lubricant that does not pick up dirt or dust and greatly increases the life of the connectors, i will put some kits together and put them up on Do not use Graphite as the 185 volt back emf pulse from the coil could arc out inside the connector and cause damage, do not use oils grease wd40 or anything like that as dirt will stick to it and cause a lot of abrasive wear on the precious gold contacts. Having good connector contact is one very important part of the detector to look after, it is a very overlooked aspect of detector performance.

This is the bad coil connector removed from the front face, note that this is a modified detector.

A new connector on a GPX-4500  Compare the pins on your own detector.