Garrett Pro Pointer problem

[Skippy]

I have a schematic that I found on a Russian forum somewhere, but I can't find it at the moment.
So here are my own notes on the oscillator part of the circuit.

[nalag46]

Do you have the schematic for the pointer ? If not, I will find my notes and try and photograph them.

Ki Skippy,
No, I haven't got the schematic. I did have a good set of notes and my own rough diagrams of parts of the circuit etc. but I have mislead them and cannot find them.
If you do have the schematic and could let me have a copy I would be most obliged. Cheers

[Skippy]

Do you have the schematic for the pointer ? If not, I will find my notes and try and photograph them.

[nalag46]

[QUOTE=Skippy;271635]Kinda hard without the actual probe in front of me....
Check the regulated 5V power supply is OK
Measure DC voltage on point TP4, it's normally set up to -3.4 Volts, though anything from -2V to -5V could work. Bring metal near the coil, the voltage rises. Normally, a rise to -3.3V will trigger the beep. If that seems OK, then the oscillator is at least functioning. Then check that point TP7 behaves similarly, probably around -2.8V DC. Then check the DC voltage going to the micro, it should be above 0 V, and usually below +2 V.[/QUOTE

I borough a friend's working pointer and got all the relevant voltage readings both in "stand by" no metal, and with a coin touching the probe. The problem appears to be in the oscillator circuit. The probe switches on and goes straight on to "detect/continuous running tone" and pressing the reset and switch button at the same time will not work.
The voltage reg. is steady at 5v. but the voltage at test point 4 with the probe running as it is, is 0v. and bringing metal near the coil will not make any difference.
On the working probe, voltage at Wp3 to the Ic is just below +1v and the same at WP2 on stand-by but going down to 0.4v driven. On the faulty probe (on continuous buzz) the readings are +1.5v. and +3v. respectively. All other voltages are the same on both. If it is the chip a 1566 id on it does no bring up any search results.

[Skippy]

Kinda hard without the actual probe in front of me....
Check the regulated 5V power supply is OK
Measure DC voltage on point TP4, it's normally set up to -3.4 Volts, though anything from -2V to -5V could work. Bring metal near the coil, the voltage rises. Normally, a rise to -3.3V will trigger the beep. If that seems OK, then the oscillator is at least functioning. Then check that point TP7 behaves similarly, probably around -2.8V DC. Then check the DC voltage going to the micro, it should be above 0 V, and usually below +2 V.

[nalag46]

It's an electrolytic capacitor, fitted across a regulated supply voltage. Capacitance is 100 microfarads, voltage rating is 16 Volts. Case diameter is 6.2mm, height is 5.5mm. The positive terminal is the one closest to the edge of the PCB.
I don't think the value is critical, 47 uF or 68 uF would work the same. Earlier versions of the PCB just had a small ceramic capacitor, no electrolytic.
You should be able to easily find something suitable in your scrap collection.

Hi again,
Having replaced the missing and faulty components (elec. cap, buzzer, switch) and cleaned out the p.c.b. for dirt and signs of water corrosion, I have a working
pointer but it is on continuous buzz (like detecting a large piece of metal with the pointer resting on it) after switch it on away from any metal.
I have checked the coil terminals for connection and resistance and all is well there. I have also checked the other large 470uf electrolytic and again it is ok and because it seems clear that it has had water damage, I am beginning to think whether the problem is with one of the ics being damaged as they do not seem to have any protection coating on the pins.
Would you have any idea on what else might cause this? After one of my last repairs, I made a chart of all the the relevant stage voltages both on "stand by and in full detect modes" but like I said before, I have mislead all of my notes and I quite stuck without this information.

[nalag46]

hi nalag46, a tip i use is when i have a bundle of notes for a particular repair is to scan my notes into my computer, and then i add them to my photo backups.
i do the same for schematics and photos of faults and repairs too, then if my notebook goes walkabout i can always find the info i need.

Thanks, that is a good tip and believe or not, I have done exactly that in the past with all my detector and other general electronic equipment I repair, but for some unknown reason I just didn't bother with the Garret's probe and I am now regretting it, as it turns out, I have a new problem with this probe that I haven't seen before and I might have to come back here and ask Skippy or anyone else with experience on these to see if the can be of assistance. And yes, I am still looking for those elusive notes.



I didn't bother with the Garret's probe and I am now regretting it

[sinclairuser]

You are a gent Sir and I am much obliged to you.
I should be able to sort it all out now. It comes with a broken switch (most common fault), a non working buzzer (being shorted our from water penetration) and I am not
sure about the vibrating motor and the light until I fit the missing cap.
It just makes you wonder what people do with these pointers. I have repaired dozens and I had built up a good set of notes, circuit and component layout but I would be damned if I can find them?? but I will keep searching because I do not throw anything away and they must be in my workshop somewhere.

hi nalag46, a tip i use is when i have a bundle of notes for a particular repair is to scan my notes into my computer, and then i add them to my photo backups.
i do the same for schematics and photos of faults and repairs too, then if my notebook goes walkabout i can always find the info i need.

[nalag46]

It's an electrolytic capacitor, fitted across a regulated supply voltage. Capacitance is 100 microfarads, voltage rating is 16 Volts. Case diameter is 6.2mm, height is 5.5mm. The positive terminal is the one closest to the edge of the PCB.
I don't think the value is critical, 47 uF or 68 uF would work the same. Earlier versions of the PCB just had a small ceramic capacitor, no electrolytic.
You should be able to easily find something suitable in your scrap collection.

You are a gent Sir and I am much obliged to you.
I should be able to sort it all out now. It comes with a broken switch (most common fault), a non working buzzer (being shorted our from water penetration) and I am not
sure about the vibrating motor and the light until I fit the missing cap.
It just makes you wonder what people do with these pointers. I have repaired dozens and I had built up a good set of notes, circuit and component layout but I would be damned if I can find them?? but I will keep searching because I do not throw anything away and they must be in my workshop somewhere.

[Skippy]

It's an electrolytic capacitor, fitted across a regulated supply voltage. Capacitance is 100 microfarads, voltage rating is 16 Volts. Case diameter is 6.2mm, height is 5.5mm. The positive terminal is the one closest to the edge of the PCB.
I don't think the value is critical, 47 uF or 68 uF would work the same. Earlier versions of the PCB just had a small ceramic capacitor, no electrolytic.
You should be able to easily find something suitable in your scrap collection.

[nalag46]

Is this where I say "A picture is worth a thousand words" ?
Is this 'cap' black in colour, with a line at one end and B2K printed on it? And there's another identical one next to the big transistor?
It's not a capacitor, it's a schottky diode. Have a rummage in your vast pile of electronics scrap , look on power supply boards, or the power parts of any board. Find a diode , ideally one that measures a forwards voltage drop of 0.2 Volts on a diode tester. Even a regular PN silicon diode will do, I guess, and there's physically room in there for a diode with leads, join it to the loudspeaker + pin and the +battery terminal.

Hi Skippy,
Been given a broken up and faulty Garrett Pinpointer and having mislead all my old notes, I cannot remember what exactly was the component that has been wrenched off the pcb shown in the attached pic. It looks like a cap or may be a coil? I am sure you know what it is and would be obliged if you let me have the details.
Thanks

[Sean_Goddard]

Hi,
Have obtained one of these Pinpointers with one component missing. It looks like the owner had a go at repairing it and ended up taking out
one of the surface mounted cap. (doubtless by using the wrong soldering iron?)
[ATTACH]37879[/ATTACH]

Why do people who have absolutely ZERO understanding of electronic think they can fix these things? Even more amazing is that they THINK they can solder too.

[nalag46]

All sorted. I even managed to find an old Schottky diode in my junk box that has a much lower forward voltage drop than a standard IN silicon type ( I tried earlier) and it seems to be working pretty much as it should.
Once again, thanks Skippy for your prompt and knowledgeable input. Best wishes.

[nalag46]

Yes, you are right Skippy. The "cap" is black and there is another one identical above the big transistor. I have an "in-circuit " diode tester and the one above the transistor reads ok whereas the "suspect" one does not, so this definitely is the problem here. These components are so small it is a job to tell what is what. I will lookout for a suitable diode tomorrow and will let you know how I got on. Thank you.

[Skippy]

Is this where I say "A picture is worth a thousand words" ?
Is this 'cap' black in colour, with a line at one end and B2K printed on it? And there's another identical one next to the big transistor?
It's not a capacitor, it's a schottky diode. Have a rummage in your vast pile of electronics scrap , look on power supply boards, or the power parts of any board. Find a diode , ideally one that measures a forwards voltage drop of 0.2 Volts on a diode tester. Even a regular PN silicon diode will do, I guess, and there's physically room in there for a diode with leads, join it to the loudspeaker + pin and the +battery terminal.