Anybody ever ever a 70 coil go bad?

[elvis earnhardt]

My X-70 was working fine. It has started chattering alot, I went back to Factory pre-sets. Still chatters. Tried all the tricks I know. When I set it down to dig a target it really raises cain! I put my other coin on and it settles down! I took off the coil cover to make sure there wasn't anything under it also. Any ideals Y'all


Mike

 

[BarnacleBill]

Sounds like interference of some nature. With no radios, cell phones etc on you. Turn sensitivity down to 15, keep coil in a fixed position away from targets or the ground, change channels in your Noise Cancel menu. Notice any change? Change geographic locations by a mile or so into a non-congested area. Same amount of chatter. Also has this coil been underwater recently? And which coil is it?

HH
BarnacleBill

 

[Dan-Pa.]

My unit is at Minelab U.S.A. as it will only pinpoint 1-2 inches but in all other facets works well. I felt it was a bad coil but am sure the Minelab tech's will let me know shortly.

Do remember coils do go out of tune and one bad solder joint at the connector to the box will surely cause the conditions you allude to....

 

[Mark in S.E. IA]

Hey Dan-Pa. Can you please explain to me how a coil can go out of tune and can you retune a ML X-Terra coil?

 

[Dan-Pa.]

Am not into the workings of detectors so certainly a question for the tech's...A good analogy would be I drive a car but sure couldn't rebuild its motor...

 

[BarnacleBill]

The most common detectors used today are referred to as VLF's. The technology used in this type of detector is call "Induction Balance" with Balance being the important word. Remember the phrase in Star Wars "I detect a disturbance in the Force". When a target is detected, the "Balance" of the detector is thrown off and it signals to you the user that we are now in an imbalanced condition. Hold that thought for a moment.

If you look at the typical coil, the outer ring is the transmit winding and the inner ring is the receive winding. If that's all the coil ever consisted of it would never work, because you have the transmit winding right next to the receive winding and the detector would be in constant overload. There is a third "ring" or winding that you don't see, it is another receive winding that acts to cancel out the transmit signal. This winding balances the detector so it remains quiet without a target nearby. The tuning of that winding is critical as is the physical positioning/shape/rigidity of the other windings in relation to it.

Temperature changes, mechanical shock, & flexing can all cause changes in the relationship of the length/spacings of those windings and de-tune the balance. This is a critical failure and will throw off being able to Ground Balance, correctly ID etc. Tuning a coil is like tuning a musical instrument in that the three windings are all interdependent and they should all be tuned in the same key.

Re-tuning an X-Terra coil is next to impossible. First is the coils are in a potting compound which is like an epoxy, even a minor attempt to remove it will damage the coil. Next is the IC chip in the coil, somehow they are unique to each individual coil with parameters stored in them for "that" coil. And when I say that, you can have Qty 10, 6 inch HF DD coils and the parameters for every one is different and stored in each IC chip. The minute you change anything about the coil it will no longer match the parameters in the IC chip. It's the technology in the IC chip that custom tunes each coil and keeps the performance uniform over large production runs. It also keeps the performance consistent from coil to coil.

HH
BarnacleBill

 

[Mark in S.E. IA]

Thanks Bill

 

[Kelley (Texas)]

n/t

 

[Dan-Pa.]

I guess Whites and Tesoro's must be different as on different occasions coils were retuned according to their tech's...I have no technical knowledge rel detectors so just assumed all coils could be retuned...I would imagine on a X-terra they just replace the coil under these circumstances...but again one bad solder joint on the coil connector can cause all kind of havoc and way back when I hipmounted heavy detectors had more than one repaired by my local TV repairman for a few bucks. As in hipmounting easy to jerk the coil wire and cause a problem with the solder connections..Thanks for the excellent input....

 

[Steve in Idaho]

My 10" DD coil windings came loose and would rattle around the coil housing. It damaged the main board in the box, so Mine Lab replaced the coil, the main board and the battery holder. It works great thanks to Mine Lab service.