The Crossbow Classic PI

[Qiaozhi]

Sorry, but as I wasn't told to do it, I didn't, despite my pal saying he thought those two connections needed doing after looking at the schematic.
After connecting 1&2 and 3&4 will the use of the adapter be necessary?
Will do the above connections tomorrow, or rather pal will as I am not very good with the iron.
Thanks again.
Picture of resister used. It wouldn't surprise me if I have used wrong type.
[ATTACH]40938[/ATTACH]

The resistor pictured is fine.
The connections between pins 1&2 and 3&4 are shown in the "Minelab DD Coil.pdf". These need to be done in the adapter cable plug (as shown), not the coil socket in the back of the electronics enclosure. If you put them in the coil socket, then the original coil will not function correctly.

[TowySalmon]

Sorry, but as I wasn't told to do it, I didn't, despite my pal saying he thought those two connections needed doing after looking at the schematic.
After connecting 1&2 and 3&4 will the use of the adapter be necessary?
Will do the above connections tomorrow, or rather pal will as I am not very good with the iron.
Thanks again.
Picture of resister used. It wouldn't surprise me if I have used wrong type.

[Qiaozhi]

But, I have installed a 470R resister between pins 2 and 4 inside control box this morning.
Currently at the back of the coil plug inside the control box, I have as stated, the resister between 2 and 4, an orange cable to 3, a blue cable to 1 and a yellow cable to 5.
Is the installation of the resister the only part of this modification?

It sounds like you forgot to add the two links in the adapter cable between pins 1&2 and 3&4. Otherwise the damping resistor isn't actually connected to anything.

[TowySalmon]

No idea about different types of resisters, sorry but I have, liked mentioned before, not an electronics expert.
But, I have installed a 470R resister between pins 2 and 4 inside control box this morning.
I then as a control, connected up the original coil and it works, so I haven't broken anything.
I then connected the adapter, then the new coil. Switched on and get the correct (I presume) threshold and nothing is detected even an inch from the coil, no change in threshold whatsoever!
Removed the adapter and connected the new coil direct to the control box. Threshold clicks present. A metal object will change the threshold up to 3" away.
I believe, that this shouldn't happen as as far as I understand it, the resister is essential so is the adapter. So what's going on p[lease experts as I am getting very frustrated.
Currently at the back of the coil plug inside the control box, I have as stated, the resister between 2 and 4, an orange cable to 3, a blue cable to 1 and a yellow cable to 5.
Is the installation of the resister the only part of this modification?

[6666]

Two x 2 watt to make up what value you need, or even 4 x 1 watt to get the power and value.

[eclipse]

Don't go for Wirewound type resistors, use only Metal Film/Metal Oxide types, at least 2W as Qiaozhi said.

[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.

[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]

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]

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]

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]

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?

[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...........?

[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]

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.