The Crossbow Classic PI

[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?

[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]

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]

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]

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]

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]

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.

[TowySalmon]

I am sorry, but I have no idea of the wiring details. Do I undo the plug at end of cable and post a picture?
As regards the adapter, it is as per the pdf document you posted here. Three wires used. 1 to 1, 3 to 3 and 5 to 5 as per diagram. Is this correct?
The coil is for GPX, GP SD series.

[Qiaozhi]

I bought a 15"x12" Detech SEF.
I have made up an adapter cable and checked for continuity.
Connected the adapter cable and turned on the machine but something is not right. The machine makes a continuous noise, but it does not click click on threshold like with the original coil. Passing metal over the coil does not change the sound.
I am quite disappointed.
Can anyone help me please?

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

[keith777]

i really hope someone comes along and can help you out on this. i would really love to see that large coil working on the crossbow.
it would be cool to see it in action in a video.

[TowySalmon]

I bought a 15"x12" Detech SEF.
I have made up an adapter cable and checked for continuity.
Connected the adapter cable and turned on the machine but something is not right. The machine makes a continuous noise, but it does not click click on threshold like with the original coil. Passing metal over the coil does not change the sound.
I am quite disappointed.
Can anyone help me please?

[TowySalmon]

I have come down to choice between two coils, 15"x12" (905gm) or 18"x15" (1035gm) Detech SEF coils for Minelab GPX, GP and SD series. I discounted the new 15" due to the cost and weight. Which of the two above would you chose? Detech tell me that both will be ok for gold and silver jewelry on wet beaches.
I will have a go at making the adapter cable as per the details previously kindly given.

[TowySalmon]

That .pdf document has made things so much clearer for me; absolutely marvelous.
Thanks so much,

[Qiaozhi]

I've just re-discovered a document I created that describes how to connect a Minelab GPX coil to the Crossbow PI.
Might be of interest ...

[Qiaozhi]

The clones that were on eBay are based on a revised PCB layout (the one I supplied to Sven) so there's no need to think that they're any less good than the originals. In fact, the recent one (which I believe was purchased by keith777) appeared to be well constructed. Most people, who have made copies, have built them for their own use. There only seems to be one person who's selling clones on eBay, and that's on a very infrequent basis.