Garrett Pro Pointer problem

[nalag46]

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?)
Can anyone please tell me what is the capacitance value of the first cap along the row of four connected in parallel where the 3 coil cable ends
are soldered? Picture attached.
Many thanks

[Skippy]

It is 100 nF, ceramic, 1206 size, I'm unsure about what type, ideally something stable with temperature. If I was repairing it, I would use a leaded polyester/mylar capacitor, there's room for it. Don't solder to the pads for the missing SMD capacitor, they will rip off. Join one lead to the end of one of the SMD caps, and find a decent 0 Volt Ground point for the other lead.
Fix the cap with a blob of glue, hot-melt, or silicone.

[kt315]

again guys I URGENTLY AND URGENTLY ask you do the images more legible.

please do these step by step!

1. wait clear sunday time. the sun must be VERY OPEN!
2. GO OUT from your home, at your homeyard, at the sunlight.
3. place PCB so the sun light will be from left upper PCB corner.
4. the shadows must be short, but they must be!
5. do a photoshooting.
6. you have NOT EVEN A TINY CHANCE here to get the answer if you are doing your Home Work poorly and woorse.
7. set your camera on high resolution. your pics has to be from 5MB and more.
8. send your pics to [email protected] with subject in subject field:
new hires pics of board [detector model name] for your collection.
9. Forget your egoistic intentions only take on and give nothing in return.
do not cultivate your EGO here.


GOOD LUCK IN THIS YOUR NEW HOBBY.

[kt315]

[nalag46]

Hi Skippy.
Thanks for that information. I connected a mylar 100nf cap and could not get the probe to pick up any metal. I tried 5 different capacitance going down from 100nf to 10nf and found the best match to be 22nf as shown in the attached pic. With this experimental cap (not necessarily the best quality one) the sensitivity is spot on but may be just on the high side and prone to slight drift/chattering. So I then tried the offset retuning by moving a piece of metal (coin) close to the probe and switching on whilst holding the reset button but my only concern is that the probe seems to be "just right" with a collector voltage of about 3.5v. I have read that the factory default voltage for this set up should be around 4.5/5v and there is a video of someone showing the best setting at a reading of around 6v, so what do you think? If I increase the capacitance slightly, the sensitivity drops considerably and offset adjustment does not seem to make much difference and at 10nf it will only pick up a manhole cover.
Cheers

[Skippy]

That 100n cap is the MAIN tuning cap for the coil. On my example, tuning caps across the coil are 100nF and 22nF in parallel, ie. 122nF. Coil inductance = 1.28 mH, giving f res = 12.1 KHz. Maybe your coil has a different L, so you may need slightly different C values to get the correct frequency.
The other 3 caps in the nearby circuitry (between the opamp output and the coil/122nF tuned circuit) are ( 10n + 2n2 + 1n0 ) = 13.2nF. This ratio of 9:1 (122:13.2) should be maintained.

Regarding the calibration, I think a TP4 voltage of 5.0V is about right, going above 5.5V is likely to cause problems on hot or cold days etc.

[mykaitch]

where can I get the schematic - I wanna make one? Thanks

[keith777]

Hi guys.

i have one of the original very first (xpointer) pinpointers that came out from china a few years back, that someome is welcome to have as a mess about with project.
when i got it. it was one of a very small hand full that was being sold at the time on ebay. when it came, on testing it out. it worked but there was a brake in the coil or something like that as it would sound off when you scrubbed the tip in the ground/in your hand etc. it sounded off to easy so it was unusable. the seller promised to send me a replacement out. but they never did.

i did have a look at the board at some point and could not see anything that looked broken off/burned out etc on eyes only viewing. not that i am n electronics expert or anything like that.lol i had noting to loose as i had gotten a refund back from good old paypal. so i decided to try and take the coil out. man was it well stuck in there. i tried first from the top all kinds of ways, but had to give up that way. so i went from the bottom by drilling a hole. then i pushed the coil out with a strong metal rod. as you can see from the photo of the coil. (these were taken back in 2014) i made a bit of a mess of it. when i soldered the coil back to the 2 wires on the board for testing. the pointer swited back on etc, but the coil had now stopped working altogether. so it got put away and forgot about.

as i say if anyone wants it as a mess about with project. they are very welcome to it. (the only thing is, the coil has gone missing untortunatly.) were you see the cable tie next to the battery cover. i had to put that on as the if i remember the plastic there in two places had two small cracks that was stopping the cap from tightening up.

[nalag46]

Hi Skippy,

I have a Garrett Pro Pointer (older black version) that was working fine but suddenly the buzzer stopped sounding. It just vibrates and detects metal ok but no sound. Have replaced the buzzer but has not made any difference and as I cannot get a circuit diagram anywhere, would you happen to know what the likely problem be?
Your advise would be most appreciated.

[dbanner]

Hi Skippy,

I have a Garrett Pro Pointer (older black version) that was working fine but suddenly the buzzer stopped sounding. It just vibrates and detects metal ok but no sound. Have replaced the buzzer but has not made any difference and as I cannot get a circuit diagram anywhere, would you happen to know what the likely problem be?
Your advise would be most appreciated.

Are you sure you replaced the buzzer with the correct type?

[nalag46]

I have used the attached model before without any problems??

[Skippy]

It's not a beeper, with internal electronics. It's simply a loudspeaker, which needs driving with an audio signal to make a noise.
The DC resistance of the loudspeaker is 50 Ohms, and there is a 100 Ohms resistor in series with it, on the pcb nearby.
Check its resistance, if it is open-circuit, then you have found your fault. If it measures about 50 Ohms, attach it to your stereo system and see if it makes a (crappy) sound. Bodge a set of earphones/headphones across the two pads on the PCB, and see if they beep when the pointer is working.

[nalag46]

The resistance of this buzzer is 35 ohms across its terminals. I have removed it and replaced it with a small 8 ohms speaker and can only get some sound (not as loud as it should be on detecting metal)
if it is connected across the 100 ohms resistor, which reads the right resistance, and the positive supply terminal (by-passing the small capacitor in line with the buzzer positive terminal). If it is connected to the
right side of the cap there is no sound and the same goes for the buzzer. However, with the buzzer connected directly to the plus supply, the full volume is restored therefore the cap must be faulty?
Do you happen to know what its value is?

[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.

[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.