I opened a 11' DD coil....

[Giantprawn60]

I have a G2 but when the coil brushes something or hits stubbles, it falses. So I decided to open the box on the DD coil. This was a struggle a bit due to the black plastic sealant but I managed. The PCB there looks like on the picture however it has no resistor like I saw on a T2 PCB picture. it's empty. But the coil worked fine unless it was touched on the specific areas on the sides. So I decided to open the coil (I have a spare Nel so I thought it doesn't matter if I break this one). Oh my god!! It is such a struggle to open! Everything is glued together. No wonder Teknetics never repairs their coils and prefer to just give a new one! Unfortunately while trying to open it, 2 things happened: the 2 thin copper wires of one of the loops broke and the 2 loops were submerged in a hard black "cement".Pretty sure it is carbon paint or epoxy. Don't know what to do with it now though...I tried to reconnect the 2 thin copper wires but there is no signal when something metal is presented. The only time the detector beeps is when those 2 thin wires move/vibrate when I touch the coil. I have put silicone on the area where the copper wires were falsing to keep them still. any ideas welcomed!

 

[lytle78]

Coil building is a black art. Hope you didn't find any Pentagrams or other weird stuff in there!

 

[Giantprawn60]

It is an art indeed! UPDATE I managed to reconnect the 2 thin wires.No wonder I was getting no signals, I forgot that they were protected by a very fine membrane. Once I removed the membrane and "reconnected" them, I had signal. Also out of the 2 falsing locations I had, I fixed one by submerging the area with silicone.the silicone hardened and kept the wires from hitting eachother and creating a false signal. However I cannot do anything with the other falsing area as it is trapped in that black hard epoxy thingy.
Anyway the coil is pretty much shot now but it was good to see how it works and how it is set up.It may come handy one day.
Just a tip though: if you have a similar problem one day just send your coil to Teknetics for replacement. It is almost impossible to fix yourself due to the epoxy, glue and the way it is set up,trust me.

 

[Sven]

The TX coil and RX coil are positioned to an exact null point. If not in the correct position the detector will not function properly.
I believe they use a black spray shielding on the coil shell and one of the ground wires gets connected to it. The circuit board is there to make sure the coil works properly.
If the coil windings are disturbed position wise even just the tiniest bit, the coil goes out of phase. An oscilloscope is needed when building a DD coil. You will find better DD coils are completly
encapsulated in epoxy. Cheap out way of building a DD coil is tape and tack gluing the coil in place on the coil shell base. For mass production units that's fine. Now you know why there are after market coils
which are 100% better constructed with better shielding as well.

 

[eSCANZ]

Thanks for that info Sven - More great stuff to take in - appreciated

 

[Ed in SoDak]

You're a brave soul! I opened a BH 4" coil, since I had three and my wife only uses the stock 8" coil. It's much simpler, but still pretty mysterious. It was filled with expandable foam, which I mostly picked away and dug out using my fingernails and small hand tools. Yeah, I lead a boring life! I Ohmed out the coils and made a crude schematic of it. I wanted to learn how it worked to DIY an even smaller coil, but the "project" didn't get far. I think it still works but I left it open as seen in the pic.

For that remaining glitch, maybe some thin glue that penetrated between windings in the black goo would stop the rattle. If you use superglue, don't try soldering there later! Cyanide fumes and nasty stuff.

I think if you're introduced to coil-building while still in the womb, then you've got a chance! LOL!

-Ed