Tesoro Coil Question

[Qiaozhi]

Here's a couple of simple questions that I'm certain some of you may be able to answer:

I have two Tesoro concentric coils - one from a Bandido that works perfectly, and a second coil from a Laser, which is suspected to be faulty. A diagram showing the connector plug (viewed from the plug end) is attached. This diagram shows the results of some measurements I have made to these two coils using an Atlas LCR meter. As far as I can ascertain, there are at least two inductors in the search head (I am assuming that one of these inductors has the nulling coil in series with it) and a possible third (very low inductance) coil. My suspicion is that the low inductance measured between pins 3 and 5 in both cases is not a real inductor, but is actually a short-circuit within the search head. The LCR meter does display a warning that this is a very low inductance/resistance measurement, so I believe that the green/purple wires are actually shorted to the screen within the search head. As you no doubt know, the Tesoro search heads are virtually impossible to take apart without destroying them, so there is no practical way to find out the answer.

Anyway, my questions are:
1. Can anyone confirm my findings?
2. Which coil is the TX and which is the RX?

I suppose it would be possible to figure out the answer to question 2 using a small coil attached to a scope probe, but this is the lazy way to get the answer. Besides, I know that Tesoro coils are commonly used in DIY projects.
My guess (looking at the wiring configuration) is that pins 1 and 3 are the TX, and pins 4 and 5 are the RX.

By the way, the suspected faulty coil does not work when connected to the Bandido, which is strange because the measurements are exactly the same, except for the presumably phantom inductance measurement between pins 3 and 5. My guess is that there is enough of an inductance variation between these two coils such that the Bandido would need to be retuned.

Any information would be appreciated.

[Qiaozhi]

Answering my own question

OK - I've carried out a few checks myself and here are my findings ->

After removing the plug to allow for easier measurement, the first thing I noticed was that the red wire was in fact orange. A simple Colpitts oscillator was then used to drive the search head via pins 1 and 3 (orange and purple). Scanning the surface of the search head with an RF choke connected to an oscilloscope revealed that pins 1 and 3 were connected to the outer coil. So this must be the TX coil. With a suitable value capacitor connected between pins 4 and 5 (grey and screen) it was then clear that the RX coil was also working ok. Moving various metal targets close to the search head showed that everthing is working as expected. It appears that my "suspected faulty" Tesoro Laser coil is in fact in working order.

Questions answered:
TX coil = (pins 1 and 3) orange and purple.
RX coil = (pins 4 and 5) grey and screen.
Pin 2 is not connected.
The purple wire is connected to the screen within the search head.

Hope this is useful information.

[quink]

Hi Qiaozhi,
a question to the Bandido coil-schematic:

- is the coil a Bandido, or a BandidoII, or a BandidoII umax ?
- is this coil the Standart coil or a special coil ?
- the Datas (mH and KHz) are the right? (because i have a coil-schematic from this Board with RX: 6.2mH and TX: 5.75mH for the BandidoII umax)

Information about the Tesoros-coils would be appreciated,
quink

[Qiaozhi]

Tesoro Coils

Hi Quink,

The known good coil I have is from a simple Bandido and it is a standard coil. The measured values were TX=5.9mH and RX=6.5mH. The second coil which was suspected as not working is from a Tesoro Laser, and has the same coil values. From looking at several Tesoro schematics and reading posts from other people, it appears to me that all Tesoro coils have the same inductance values and the same pin connections.

There is a thread in the schematics forum entitled "Unknown Tesoro Schematic" where the pin connections are shown as TX = orange (1) & shield (5) and RX = violet (3) & grey (4). This is slightly different to my conclusions on the correct wiring scheme. Since the violet and screen wires are connected together in the search head, this probably somewhat academic. I suppose it depends whether you consider the TX or the RX wiring requires the shielding.

In tests I have made with these coils, they seem to give good performance at any frequency from 10KHz up to 20KHz. There are no capacitors or resistors in the search head, and the transmit frequency is determined by capacitors in the TX circuitry of the control box.

[bobsyn]

Hi all! Sorry for my bad english.
I need all data for BANDIDO II nMax coils.

Thanks
[email protected]