GA-72Cd Magnetic locator

[ionut_mtb]

I have a GA-52 and two GA-72Cd's. On the GA 72 the green switch 5pos . Is on/off, L, M, H and XH gain. I think it switches the 4 resistors that are near

Wanted to reverse the GA-52 pcb, but never got around to it. It uses a RC4152 for the vco, The tx/demod oscillator is HEF4047, DC-DC ICL7660,,OP421, OP421. CD4053. The blue chip is a 10K resistor array.

Here are some photos of the pcb

Hello Altra. Thanks for helping. Do you have some pictures on how 3pin piezo is connected? Someone worked before on this and the piezo wires were disconnected.

[Altra]

Hello Altra. Thanks for helping. Do you have some pictures on how 3pin piezo is connected? Someone worked before on this and the piezo wires were disconnected.

Hi. on my unit the piezo is 2 pins. A two wire jumper runs up to the headphone jack. The volume pot has 3 wires?

[Altra]

Piezo connections

[ionut_mtb]

Hi. on my unit the piezo is 2 pins. A two wire jumper runs up to the headphone jack. The volume pot has 3 wires?

Yes, same like you. Volume pot has 3 wires, piezo running 2 wires to the headphone connector area. Piezo has 3 pin but one pin wire to the pcb is going no where - on the pcb is no copper trace.

[ivconic]

Hello Ivconic, thank you for helping me.
I will try to reply on all your post but is hard from the mobile phone.

#2 - that side of the pcb is exactly how you described but 555 pin 3 does not go to the piezo/headphone, it goes into the yellow resistor network (ladder).
#5 - i tried to remove the sensor for you but I cannot pull him out from the case and i’m afraid damaging it…
#6 - it is a switch - on/off and gain settings (L, M, H, XH) si it is a 4 position switch.
#7 - i don’t know much and i’m not so interested in it because my time for metal detecting is very limited for now (lost of interest unfortunately- maybe because of hot weather) but i can inspect more if you want. This device is for industrial use - a friend has it. Two CuEm wires (from the pcb coil) going inside the shaft and 3 small insulated also.

The pcb had a lot of corrosion on some pins and i tried to resolder and clean. The result is: device not power on anymore

I was right about LM2931, it is low drop voltage regulator. There must be additional inscription bellow "LM2931" about the voltage, is it 5v or something else.
https://pdf1.alldatasheet.com/datash...MI/LM2931.html
...
What can you do else?
Check the power supply and voltages at all opamps and chips.
It is easy at quad, dual and single opamps, pins are standard.
There must be a reason for faint and low audio. Usually it is voltage drop somewhere of some faulty component.

[ivconic]

When you upload photos directly in your post (also you can Copy&Paste into) , once photo is inside the post "box"; you can resize it by clicking on the bottom right side of the image and pull it up and left.



To avoid exra large image across the whole display.
Because it is aesthetically more acceptable that way, it is easier to follow the post and the entire page on the topic.
Image resolution remains unchanged, who wants to see details; simply click on the image and zoom in to detail.
Forum engine is fine. You just need to get used to the new functions and find methods for manipulating the elements in the post.
I "hated" this engine and was very angry when Carl switched to it.
But over time I got used to it and now I like it better than the older one, because it has more options and it's easier to manipulate the elements.
A good trick is to "throw" random elements into a post, click "post" or "reply" and then see how it looks and then immediately go to "edit" the post.
Do edit fast because of the timeout time that Carl (because of my fault) reduced.
And only in edit mode you have a very good overview of the elements in the post and only then can you edit the post aesthetically very well.

[ionut_mtb]

I was right about LM2931, it is low drop voltage regulator. There must be additional inscription bellow "LM2931" about the voltage, is it 5v or something else.
https://pdf1.alldatasheet.com/datash...MI/LM2931.html
...
What can you do else?
Check the power supply and voltages at all opamps and chips.
It is easy at quad, dual and single opamps, pins are standard.
There must be a reason for faint and low audio. Usually it is voltage drop somewhere of some faulty component.

It is LM2931AZ-5 so 5V regulator. I will check the power supply in all ICs. Thanks

[ivconic]

... i don’t know much and i’m not so interested in it because my time for metal detecting is very limited for now (lost of interest unfortunately- maybe because of hot weather) but i can inspect more if you want. This device is for industrial use - a friend has it...

Ah so, it is not your own device?
I am interested to see what such device can do in reality on "militaria" kind of targets.
Say... metal box 40x40x40 (for example) put in a 2 meter deep hole (no need to cover the hole at this time) and see if the device will make any response to it at all.
In case it makes an response; than it is excellent and than I would be very interested to make/copy something similar.
A guy sent me in the past short video of some Ebinger, achieving exactly that, a nazi helmet was in such hole and easily detected with such device.
I was impressed.
Unfortunatelly I lost link to that video, I can't find it on Youtube. It is because the title was in Czech or Polish with special characters (I think) and now it's impossible for me to reproduce any search term on Youtube.
And maybe the video was removed from the channel in the meantime. I don't remember who sent it to me. I am very sorry that I did not download that video to my computer.
I may have added that video to one of my posts here on the forum in the past, but I can't find it now.
But from what I saw it; I was impressed, and since then such devices are very interesting to me and I want to make or acquire something like that.
Of course... money is always a problem, such a new "Ebinger" is far beyond my means.
If I am not mistaken, if I remember correctly; it was an Ebinger Magnex 120 model.

[Orbit]

Two meters is a problem to detect an iron object of size 40 x 40 .. But only on the test site! The reason is clear in reality there is a lot of iron waste everywhere that hinders the searc!

[ivconic]

Two meters is a problem to detect an iron object of size 40 x 40 .. But only on the test site! The reason is clear in reality there is a lot of iron waste everywhere that hinders the searc!

It is not common detector. It is magnetometer/gradiometer and small trash can be ignored by using various tricks and techniques.
One can skip anything from a smaller iron (any magnetic) items scattered at shallow depths and "detect" ONLY larger objects at greater depths.
It is easy with refined magnetometer/gradiometer, no problem at all.
Though; the video I was talking about is made on testing hole, true.
But I am experienced enough to judgde about what I saw.
Ebinger Magnex 120 model is a real deal.

[Orbit]

It is not common detector. It is magnetometer/gradiometer and small trash can be ignored by using various tricks and techniques.
One can skip anything from a smaller iron (any magnetic) items scattered at shallow depths and "detect" ONLY larger objects at greater depths.
It is easy with refined magnetometer/gradiometer, no problem at all.
Though; the video I was talking about is made on testing hole, true.
But I am experienced enough to judgde about what I saw.
Ebinger Magnex 120 model is a real deal.

If you apply any method of avoiding small iron objects, then the range is limited.. Maybe you know what you're talking about, but I do too, I made these devices and had insight into various types of magnetometers.. Believe what you want, but it's not that easy! If it were easy, my grandmother would fix TVs too..I'm sorry, Ivica, we can discuss this on the phone and we can see each other if you convince me otherwise, I will publicly write that I was wrong... greetings!

[Orbit]

Originally posted by ivconic View Post

It is not common detector. It is magnetometer/gradiometer and small trash can be ignored by using various tricks and techniques.
One can skip anything from a smaller iron (any magnetic) items scattered at shallow depths and "detect" ONLY larger objects at greater depths.
It is easy with refined magnetometer/gradiometer, no problem at all.
Though; the video I was talking about is made on testing hole, true.
But I am experienced enough to judgde about what I saw.
Ebinger Magnex 120 model is a real deal.

If you apply any method of avoiding small iron objects, then the range is limited.. Maybe you know what you're talking about, but I do too, I made these devices and had insight into various types of magnetometers.. Believe what you want, but it's not that easy! If it were easy, my grandmother would fix TVs too..I'm sorry, Ivica, we can discuss this on the phone and we can see each other if you convince me otherwise, I will publicly write that I was wrong... greetings!

Slow sampling will cause it to be less sensitive, but fast sampling from the sensor will be super sensitive with a range that is fantastic on the table, but outdoors it is very difficult to tamper with that device!I don't think I even need to mention it because I know you know it yourself.

[Orbit]

I will not interfere in the topic so as not to offend anyone, because that is not the point, but an exchange of opinions..For me, all members of the forum are one big family, that's how I experience it.

[ivconic]

[ivconic]

One of the simplest "tricks" that a beginner learns first is what I drew.
If there is a large metal object in the depth and some metal debris/trash/smaller objects at shallower depths in line above it, as in the picture;
by simply lifting the sensor tube from the soil surface: "signals" or "anomalies" in the magnetic field on the soil surface are eliminated.
To correct myself; "eliminated" is a misnomer.
Those "anomalies" are still there, but they represent an insignificant change in the overall "anomaly" represented by a large object at greater depth just below.
Further lifting of the sensor tube; those small changes become even smaller, insignificant and do not interfere with the correct and accurate location of a much
larger "anomaly" in the soil magnetic field, which is represented by a larger object at a greater depth.
So that surface "garbage" does not represent any problem in locating strong "anomalies".
"Military" finds such as helmets, remains of weapons, various chests... these are "HUGE" anomalies in the eyes of the magnetometer.
The sensor tube can be carried at a height of 1 meter (and more) in search of such findings.
Well, it's just one of the simplest "tricks" to solve the problem of surface debris.