The Crossbow Classic PI

[Qiaozhi]

Checked adapter. Changed connections and retried. Still same. Very noisy. Connected original coil=perfect. Tried adapter again and noticed that after a while the red battery light did not go completely off, remained on, but very dim.
I think I had better wait to see if it is suggested here for me to take apart new coil cable plug.

As I said before ... Can you post the wiring details of the Detech coil and your adapter cable. Then we can figure out what's wrong.

To be more specific. we need:

1. The details of the coil (inductance, resistance, and which coils are connected to which pins.
2. Details of the adapter cable (pin connections at the coil end, and also at the detector end).

A wiring diagram from coil to detector would be best.

[TowySalmon]

Thanks.
I have written to Detech.
Do you suspect that the wiring on the new coil is different to that on the .pdf document you posted?

[Qiaozhi]

Thanks.
I have written to Detech.
Do you suspect that the wiring on the new coil is different to that on the .pdf document you posted?

Is the Detech coil a mono or DD?

[TowySalmon]

A DD.
You asked "Can you not check the continuity of the coils at the plug? That should tell you which pins are connected to the TX and RX coils."
As you know, my technical experience is next to none, so I phoned a friend. Was told to test the 4 coils I have for an Explorer and 3 coils I have for a Sovereign, to practice first. I did and all the Explorer connections were the same on each coil 1 to 2 and 3 to 4.
On the Crossbow I got 1 to 5, 1 to 3 and 5 to 3. See picture

I then went and did the SEF coil plug. I mapped it out in a diagram as I went. Please see the result in picture. I suspect that it shouldn't be like that?

Plug pins are per this next picture:

[Qiaozhi]

A DD.
You asked "Can you not check the continuity of the coils at the plug? That should tell you which pins are connected to the TX and RX coils."
As you know, my technical experience is next to none, so I phoned a friend. Was told to test the 4 coils I have for an Explorer and 3 coils I have for a Sovereign, to practice first. I did and all the Explorer connections were the same on each coil 1 to 2 and 3 to 4.
On the Crossbow I got 1 to 5, 1 to 3 and 5 to 3. See picture
[ATTACH]40904[/ATTACH]
I then went and did the SEF coil plug. I mapped it out in a diagram as I went. Please see the result in picture. I suspect that it shouldn't be like that?
[ATTACH]40905[/ATTACH]
Plug pins are per this next picture:
[ATTACH]40906[/ATTACH]

I think you have the wiring mixed up. Pins 1 and 5 only need to be shorted together for a mono, as the single coil acts as both TX and RX loops. If you're using a DD, then you need to separate the TX output from the RX input.

According to some images from Google, all Minelab DD coils have TX between 1 to 2, and RX between 5 to 4 (with 4 shorted to 3 inside the coil plug).
Basically (for Crossbow) you need to connect the Minelab TX coil between pins 1 and 3, and the RX coil between pins 5 and 3. Pins 2 and 4 can be used to connect a damping resistor across the TX coil, with the resistor connected to the back of the coil connector in the enclosure. If the TX coil is critically damped correctly, and the coil balance is good, then you won't need a second damping resistor across the RX coil. I have a Garrett DD coil connected to an MPP that works well with only one damping resistor.

Please see attached diagram.

[TowySalmon]

I am very sorry but I only half understand your reply.
What wiring do I have mixed up? I see now that the previous wiring diagram (posted 22 Oct') isn't relevant to current situation as new DD document posted. Thank you.
What I have drawn from continuity results for SEF coil cannot be right surely? I have tested continuity on lots more coil plugs now and all for Sovereign are equal, with just two connections, 1 to 2 and 5 to 6. With the SEF coil, seems like everything connected to all as per my diagram. Damaged coil? Incorrect soldering in plug?
Also you say that "Minelab DD coils have TX between 1 to 2", yet on the new diagram 1 to 2 is RX. Think next bit about pins 5,4 and 3 refer to TX? Which is correct please, statement above or diagram?
I just have a horrible feeling I have a duff coil as suggested above.
If we just pretend for a moment, it is a working coil, all I have to do is make up an adapter cable as per the Minelab DD coil .pdf and it will then work?

[TowySalmon]

As mentioned previously, I contacted Detech asking for "The details of the coil (inductance, resistance, and which coils are connected to which pins.).
Can you help with this information please?"
This is the reply.
"Hello,

1. When we declare a coil for a specific metal detector, we do not encourage using this coil for any other metal detector.


2. The technical and constructive details of the products are, if not exhibited on our website, a matter of intellectual property. We do not disclose the technical details, other than the very general ones. We make the best coils on the planet and, in order to preserve our advantage, we have to keep technical stuff as an industrial secret.


3. We do not provide consultancy for modifying our products or adapting them to solutions we did not test ourselves, nor do we encourage that.


4. Please note that any modification of the original products will void the warranty.


Best regards,
Daniel Matei
Detech Intl."

Not very helpful eh.

[Qiaozhi]

I am very sorry but I only half understand your reply.
What wiring do I have mixed up? I see now that the previous wiring diagram (posted 22 Oct') isn't relevant to current situation as new DD document posted. Thank you.
What I have drawn from continuity results for SEF coil cannot be right surely? I have tested continuity on lots more coil plugs now and all for Sovereign are equal, with just two connections, 1 to 2 and 5 to 6. With the SEF coil, seems like everything connected to all as per my diagram. Damaged coil? Incorrect soldering in plug?
Also you say that "Minelab DD coils have TX between 1 to 2", yet on the new diagram 1 to 2 is RX. Think next bit about pins 5,4 and 3 refer to TX? Which is correct please, statement above or diagram?
I just have a horrible feeling I have a duff coil as suggested above.
If we just pretend for a moment, it is a working coil, all I have to do is make up an adapter cable as per the Minelab DD coil .pdf and it will then work?

Sorry.
I said "According to some images from Google, all Minelab DD coils have TX between 1 to 2, and RX between 5 to 4 (with 4 shorted to 3 inside the coil plug)." but it should have been the other way round. My mistake.
Have a look at the attached diagram, which is the one I was referring to.

Which Minelab detector is the SEF coil intended for?

[TowySalmon]

It is for the GPX, GP, SD series: https://detech-metaldetectors.ro/en/...lab-gpx-series

I do though fear that after doing continuity that something is not right...........?

[TowySalmon]

Had a pal round today who has some electrical experience and is better with soldering. He has been detecting with PIs for 30 years too.
We used new plugs and made up the adapter cable as per the schematic. Have photographs if required as proof of correct construction.
Only half success I am afraid. The threshold now as when the original coil connected=clicks, but no metal is detected at all.
Would you expect the coil to work if there is a problem with the 470R in the control box?

[Qiaozhi]

Had a pal round today who has some electrical experience and is better with soldering. He has been detecting with PIs for 30 years too.
We used new plugs and made up the adapter cable as per the schematic. Have photographs if required as proof of correct construction.
Only half success I am afraid. The threshold now as when the original coil connected=clicks, but no metal is detected at all.
Would you expect the coil to work if there is a problem with the 470R in the control box?

Please post the photos so we can take a look at the wiring.

Do you have access to an oscilloscope?

[TowySalmon]

If the pictures are not clear enough, I am happy to re-try. The heat shrink has not yet been shrunk so all still exposed.




No oscilloscope.
Just spoken with pal on phone and he asked me to do some continuity tests on the control box cable connector and then ask the following given the results I had.
Would you expect continuity between pins 3 and 4? There is none.
Would you expect a resistance value of some sort or 470 ohms between pins 2 and 4? There is none.
Would you expect continuity between pins 1 and 2? There is none.
I again am so glad you are helping and I hope the above is of use.

[Qiaozhi]

If the pictures are not clear enough, I am happy to re-try. The heat shrink has not yet been shrunk so all still exposed.
[ATTACH]40918[/ATTACH]
[ATTACH]40919[/ATTACH]
[ATTACH]40917[/ATTACH]
[ATTACH]40920[/ATTACH]
No oscilloscope.
Just spoken with pal on phone and he asked me to do some continuity tests on the control box cable connector and then ask the following given the results I had.
Would you expect continuity between pins 3 and 4? There is none.
Would you expect a resistance value of some sort or 470 ohms between pins 2 and 4? There is none.
Would you expect continuity between pins 1 and 2? There is none.
I again am so glad you are helping and I hope the above is of use.

OK - I think I know what the problem might be.

The original Crossbow detectors do not have a 470R resistor between pins 2 and 4. That's a modification you need to do if you want to use a commercial coil, or one you've made yourself. This is because the original 10" coil has the damping resistor built into the coil shell. I incorrectly assumed that you were aware of that.

If you remove the rear of the enclosure and examine the back of the coil socket, I would bet that there are only 3 wires connected, and no resistor. This would explain why the detector is erratic, as the receive signal will be ringing horribly.

[TowySalmon]

Thanks again for your help.
I have removed the rear and as you predict, there are just three wires.
With the current adapter there isn't the horrible noise as with the incorrect adapter. The threshold click seems good.
So I need to get a 470R and install; anything else to do?
Looked on Maplin website, https://www.maplin.co.uk/search/?text=470R+ohm+resistor which one please?

[Qiaozhi]

Thanks again for your help.
I have removed the rear and as you predict, there are just three wires.
With the current adapter there isn't the horrible noise as with the incorrect adapter. The threshold click seems good.
So I need to get a 470R and install; anything else to do?
Looked on Maplin website, https://www.maplin.co.uk/search/?text=470R+ohm+resistor which one please?

Ideally I would fit a 5W resistor, but a 2W will work ok.