Garrett Pro Pointer problem

[Skippy]

Post number 28 has part of the schematic, Inductance is shown as about 1.3 mH. I guess if you wind with the same diameter wire, you will end up with the same resistance, or close enough.

[nalag46]

Thanks. The coil's wire has been cut/torn and it does not appear to be complete as there is only one end intact, the other has snapped at some stage and is not in the casing? I have straightened it out and measured it at about 2m in length, but I reckon there could be another 1/2 meter missing? I have got some cable of the same gauge and after rewinding it tight on the rod, there is no response. It would be helpful if I could see a picture of the wound-length of a working coil, but cannot find any photos.

[nalag46]

Garrett Pointer

Using a Coil32.net coil ferrite calculator online, based on known inductance of 1.3mh, ferrite parameter of 12m width x 72mm length on 25swg 0.51 copper cable, it calculates a total of 142 turns for a length of 72.36mm which is just a bit too long for the ferrite length. I haven't got an inductance meter so I nevertheless wound the coil by some 130 turns so to fit but it is not working. After checking some of my old notes, I have just realized that this circuit board is not the same as the Garrett's original. Do you know is this is an updated board or have I just landed a Chinese goose? The coil for a start does not use the earth connection that we had on the older boards, the on/off switch is a different type albeit, a more reliable one than the previous, some of the components are different and none of the caps have a printed value on them, also the reset button is no longer there either. The serial no. on the back of the cap appears to be genuine as per Garrett series 544plus and pointer's body seems ok too. What do you think?[ATTACH]58089[ATTACH]58090

[Skippy]

It's a Chinese job, and not even a good clone of the original.
There are actually two different versions of the genuine Garrett 'Original' Propointer PCB, though they are electrically the same, or almost the same. But yours is neither.
That explains why you're able to get the coil out of the probe. The Garrett ones are fixed in with a generous amount of potting resin, and you would only extract it by cutting the case apart.

[nalag46]

Hi Skippy,
I have got a used Garret Pro Pointer AT (The CarroT) that is working fine except it lacks sensitivity (these have three settings for that) and on the third setting it will only pick up a large 50p coin at no more than 1" from the coil tip, which is quite unremarkable considering this probe is rather sensitive even on the lowest setting. I have tried adding two or three small capacitance across the coil tuning caps but there does not seem to make any difference. If you have any suggestions they would be much appreciated.
Thanks.

[Skippy]

I've not got much experience of the propointerAT. The coil is not sealed in with potting compound ( like on the standard propointer ) , it's open and exposed to water, condensation etc. So I think ensuring the coil/rod assembly is properly dry would be one thing worth doing. There's no 'master calibration' feature on the AT, it may be done via the in-circuit serial programming port, I don't know. But there's no obvious way of recalibration, unless some wierd button-push does it ... I've never read anything online about such a procedure.
Dirt ingress is the usual problem, so ensure it's clean.

[David_1]

so many pictures but it would be nice to see both sides of the same pinpointer or find someone who has already draw it out, they must of sold Millions how come no drawings ???

[Carl-NC]

There's no 'master calibration' feature on the AT, it may be done via the in-circuit serial programming port, I don't know. But there's no obvious way of recalibration, unless some wierd button-push does it ... I've never read anything online about such a procedure.

The Propointer is an "energy theft" design that's akin to BFO (proximity effect). It is automatically calibrated every time you turn it on.

[nalag46]

I've not got much experience of the propointerAT. The coil is not sealed in with potting compound ( like on the standard propointer ) , it's open and exposed to water, condensation etc. So I think ensuring the coil/rod assembly is properly dry would be one thing worth doing. There's no 'master calibration' feature on the AT, it may be done via the in-circuit serial programming port, I don't know. But there's no obvious way of recalibration, unless some wierd button-push does it ... I've never read anything online about such a procedure.
Dirt ingress is the usual problem, so ensure it's clean.

Thanks Skippy,
I have borrowed a friend's AT, dismantled it (after asking his permission), and found that both are practically identical. Checked voltages and other readings on both of them and there was no difference between the two, the only item I found to differ is the coil's inductance. On my friend's good working order one, the reading is 1.225mh and on this one is 1.205mh and all three trimming caps are identical in values. Not a lot to cause such a drop in performance, I am sure, but his on the third and máximum setting the sensitivity picks up a large coin up to 8-9 cm, whereas mine only manages 3-4 cm. As you say, there is no calibration or push button feature of any kind and the coils, although not sealed in the casing, are well protected with a good wrap of sticky insulation tape, and they fit snugly in their case. They advertise these as All Terrains and therefore waterproof. The speaker grill is only cosmetic as there are no gaps through to the inside and the push button gaiter is sealed so to remove it has to be cut off. Picture attached.

[Skippy]

@Carl:
" It is automatically calibrated every time you turn it on."

I was referring to the Master Calibration, not the 'every switch-on' calibration. Master cal makes the micro adjust a 10K EE-pot so that the oscillator amplitude is 'correct' . This is initiated via the push-button switch on the circuit-board. See post #28 for details.

However the AT (Carrot) has no such button. It may have the EE-pot, I've not looked. It's possible the master cal is initiated during the micro flashing process.

@Nalag:

You have too much confidence in the 'water-tightness' of your carrot, considering it's 'used' . The rubber button can fail, the battery compartment is a leak point, no one ever bothers putting silicone grease on the O-rings. So moisture is still my main suspect. Followed by a cracked ferrite rod. Unsolder the rod assembly from the PCB, and put it in a cool oven, say 60 degrees C, drive out any trapped moisture.
One obvious test would be to swap the ferrite rods over. but as the good one is not your personal one, it's probably not advisable.

[Carl-NC]

OK, I see now.

[nalag46]

@Carl:
" It is automatically calibrated every time you turn it on."

I was referring to the Master Calibration, not the 'every switch-on' calibration. Master cal makes the micro adjust a 10K EE-pot so that the oscillator amplitude is 'correct' . This is initiated via the push-button switch on the circuit-board. See post #28 for details.

However the AT (Carrot) has no such button. It may have the EE-pot, I've not looked. It's possible the master cal is initiated during the micro flashing process.

@Nalag:

You have too much confidence in the 'water-tightness' of your carrot, considering it's 'used' . The rubber button can fail, the battery compartment is a leak point, no one ever bothers putting silicone grease on the O-rings. So moisture is still my main suspect. Followed by a cracked ferrite rod. Unsolder the rod assembly from the PCB, and put it in a cool oven, say 60 degrees C, drive out any trapped moisture.
One obvious test would be to swap the ferrite rods over. but as the good one is not your personal one, it's probably not advisable.

I cannot see any signs of moisture/condensation on the coil or inside the probe plastic casing. I will however follow your suggestion of drying it out with some form of heat and see if it makes any difference. I returned the working probe to his owner but, I did do the ferrite "swap", naughty, but I had to be 100% certain. With that connected it worked much better, say up to 90% of what the performance should be and just a fraction less than the good and newer working probe. So, it has got be the coil???

[nalag46]

I cannot see any signs of moisture/condensation on the coil or inside the probe plastic casing. I will however follow your suggestion of drying it out with some form of heat and see if it makes any difference. I returned the working probe to his owner but, I did do the ferrite "swap", naughty, but I had to be 100% certain. With that connected it worked much better, say up to 90% of what the performance should be and just a fraction less than the good and newer working probe. So, it has got to be the coil???

Have contacted Regton, Garrett's main dealer and they say a replacement coil is not a sale item. I bet if I were to send them the probe they would replace without any problem and charge my accordingly?

[Carl-NC]

Did your pinpointer used to work, and then it stopped working?

[nalag46]

Did your pinpointer used to work, and then it stopped working?

It isn't my pointer, it belongs to a friend detectorist. He quotes it has been working fine for a long time but with a reduced level of sensitivity
that latetly got much worse.