Can a coil go bad?

[Finderskeeper]

I've been a Minelab Excalibur user for many years. I've modified all 4 of mine that I have had and have never have had a problem till now.

I've run the WOT coil on my most recent Excalibur II now since it was new. It has the remote switch, 1600 MAH battery and straight shaft. But I was having edge of water stability problems with the WOT and the coil is kind of a pain when in the deeper water. So I decided to change back to the factory coil. I tested it and it worked fine for about a week and then started having static crash problems. Like an AM radio in a thunderstorm, it was making so loud a noise that it almost becomes impossible to hear the signal. I've checked the connections and all is well.

Now I've done some research and I hear that when a coil goes bad, which I did not know was possible unless it is cracked, it has many symptoms like static,instability and the inability to locate targets.
Well my machine still locates targets fine but it has static crashes that are extreme. This factory coil has never been in the water and has just a week of use. I put the WOT coil back on and all is well.

Is it possible that a coil from the factory can go bad even if it is not cracked? Again, it worked fine for about a week and then all the noise. I am kind of at a loss to figure out what is going on.

I am looking at the 10 x 12 SEF coil for the Sovereign GT as a replacement for the WOT and now the factory coil. Any opinions on the SEF for in the water work? Edge of salt water?

 

[Suncoast Kid]

As you probably know, the SEF 10 x 12 is one of the favorites with Sovereign users. The only remark I can make is that it offers a little more drag in the water than the 8 or 10" Tornado, or Sun Ray S-12, but not that much that it should be a problem. Yes, like everything else, coils do go bad. Cracks can be very small and hard to see, but since you didn't have it in the water, I don't think that is the cause. It could also be the coil wire, or the connector between the wire and the coil, or just something in the coil itself. By putting the WOT back on and having it work as normal proves that it's the coil and not the detector. I have the pre-tornado 10" on mine, and I'm about to replace it with the SR S-12. Wish you the best of luck with your mod.

 

[Critterhunter]

9.99 times out of 10 when a coil is acting up it's due to a short in the cable. Start at the base of the cable right at the coil and wiggle your way up every few inches or so until you run the entire length and get to where it plugs into the detector. Make sure you are away from EMI and have it in Auto so you can tell instability/stability at moments from just random EMI.

Should you not find the problem there, the next bet is going to be the coil connector it's self. Far harder to diagnose. Try wiggling the connector. If nothing happens try unscrewing it all the way so it's only just plugged in and then wiggle it. Should you not notice any difference that still doesn't mean it's not the connector because it's hard to move the internal pin parts of it. You can have connector pins that are not making good contact. Visually inspect them to see if the holes in them that mate with the other plug are not smashed close, and that they also aren't opened too wide. they are designed to squeeze over the pins of the other connector they mate with.

If you don't see a problem there, I've ran into coil connectors where the pin it's self is broke between the mating side and the back side where it is soldered to the cable wire. That one drove me nuts trying to figure out the problem, because when I tested both ends of a pin with an ohm meter I wasn't showing any resistance (or infinite resistance either). Only after I happened to bump the back side of one pin did it just easily fall off and show me it was broken inside.

I started wiggling the backsides of other pins and found several that just broke/fell right out of the back side of the plug. Too much heat when they were soldered to the wires at the factory is my guess, as those pins are pretty thin back there where the wires are soldered on some cheaper plugs. If you don't want to wiggle to the point of seeing if they break off, then get an extra set of hands and one person holds the ohm meter leads to both sides of the pin while the other guy wiggles the back of the pin a little to see if the resistance starts roaming up and down on you.

If none of that stuff pans out, my next guess is that the pre-amp (found almost exclusively on BBS machines to enhance weak signals right at the RX coil) has a component on that little circuit board that has gone bad. The other possibility is that the coil windings have lost a bit of their varnish in one tiny spot and are shorting to nearby windings. Rare for that to happen though with coils where the windings are encased in solid epoxy to keep them from moving out of balance.

Was it very sunny and hot out? If it was, one more possibility. The windings might have been almost out of alignment as the epoxy cured, and with extreme temperture changes the windings are distorting just enough to take it totaly out of tune beyond the ability to stay stable any more. Try using the coil after it's cooled down inside the house. If it works fine for a while and then starts getting eratic in the heat or sun then there's your answer, but it could still possibly be just a cable/connector short that doesn't show it's self until the tempertures are just right to cause the short.

Far as I know a coil filled with epoxy is pretty much impervious to water destruction even if the case has been breached. One friend had an 8" BBS coil on his Excal that was so worn down that the seams on the sides of the coil had split open, yet it still worked fine in the water. I think the bigger risk is water getting down the coil cable wires by wicking action and migrating to the pre-amp, but that would be hard to do because on the few Sovereign/Excal coils I've seen cut apart even the pre-amp is encased in epoxy.

 

[Finderskeeper]

Thanks CritterHunter. I did your test and found that the cable into the coil was the problem. I doubt I can fix it so I will just have to get the 12 x 10 SEF which is kind of what I wanted to do anyways.