TESORO GOLDEN SABRE

[ivconic]

Hello,George!I had the same problem first.It turned out IC 4024.I replaced it ,and everything is okay about sound.I have a quiestion to experts.When I null with scope at pin 7(Lf353) ,and then measure the same pin with multimeter I read about -180mV.There is some sensitivity -1euro about 10sm.When I null at pin 7 with multimeter -it shows 5-10mV -the scope shows that is not nulled at all.I tried with two different pcb-s -1265 and the last one for the schematic above.Can this be a coil problem,or something else?Pin 1 of LF353 has broken graphic too.I turn this broken graphic into a nice sinusoide by placing 100pf paralel with 100k rezistor (Lf353)The same effect may get by replacing 2,2k (emiter 2N2907) with 4,7k.But the main problem is coil nulling -the meter and scope show different place of nulling coils.

Ehh...
You should use my method of nulling - direct connection of millivoltmeter to RX coil. That way you would null coil properly and void any further doubts about it.
Else.... C9 and C10 capacitors must be PERFECT. Use high quality ceramic.
If still you can't get pefrect sinus on opamp output....than replace values 100pf with 56-68pf. Experiment....you'll manage to make it to work properly.

[GeorgeGW]

i appreciate for your help
thanks a lot!! i will try to fix it...
( sorry but i'am a student and i'am electrician and i dont know very well electronics... just a few things only... the basics!! )

[peih]

Hello everyone, I made the scheme from the first page, and made a coil of 10 khz, 18 millimeters works perfectly coin in air 30sm but discrimination is a little low iron counts always a way to make a strong diskriminatsiyata.</span>How to reinforce discrimination.sorry for bad English</span>

[GeorgeGW]

TGS PROB

hi ivconic and Pompey, i checked voltages and they are all ok... 7.9 and -6.26, i also checked the opamp supply voltages and they are ok.... i replaced 2 chopper tranzs and the buffer tranz, the chopper with 546 , 556 and the buffer with 546 and the 4024.. but the problem with continues sound remains!!!!

[ivconic]

hi ivconic and Pompey, i checked voltages and they are all ok... 7.9 and -6.26, i also checked the opamp supply voltages and they are ok.... i replaced 2 chopper tranzs and the buffer tranz, the chopper with 546 , 556 and the buffer with 546 and the 4024.. but the problem with continues sound remains!!!!

Ok, than only one thing left; those 3 diodes from 4024. One of those (or 2 or all 3) are shorted. Replace them all.
If that not solve the problem...than i don't know what else!?

[GeorgeGW]

3 diodes are ok.... so.... i put it in the box.... and i will try in the future one time to print another pcb and i will start from the beginning
thanks for all!!
GeorgeGW....

( i'll try to construct another metal detector now..... )

[ivconic]

Well...what to say? I made over 40 TGSL's so far. Each of those is workable until today. Many people on this forum also succeed to make it correctly. In my country here also i know at least 20 people that made it and still using it as main detector.
Maybe you should buy detector from a shop? It is not given to anyone to make detector just like that.

[GeorgeGW]

I dont leave it for a detector from a shop, i made two detectors ( delta-pulse and Garys PI detector ) and works good.... i will try it again from the scratch with new pcb with the same parts, I know TGSL is a good detector.

[Dennis the Mennis]

Dennis, what is so hard about finding good quality capacitors?

You should use polyester or Mylar film caps for most. Polycarbonate is also good or maybe better but hard to find.

Use Polystyrene or polypropylene for the transmit tank and also the receive tank. These are desirable because you want low loss and temperature stability. Polyseter is mediocre but much better than any ceramic cap you'll likely find that's big enough to work here.

Ceramic capacitors might be OK in some places but you had better understand the differences and select wisely between Z5U, Y5V, X5R, and COG/NPO if you want decent performance. You also need to understand voltage derating before you employ ceramic caps, even more so than for film types.

Ceramics can be used some places, but not a good idea unless know the cap's specs and choose wisely after some research.

Hi Porkluvr ,

Thanks for your reply ,
It was not the problem finding good quality capacitors but more which type should be used ...
Your answer gave me enough food for thought so guess which internet sites were visited these couple of weeks.

I've found some 'inspiration' of the condensator types used on one of the photos posted somewhere in this hugh thread .
I guess I picked the wrong photo ( perhabs from somebody with the some problems: Nelson ?...) , recently I saw other photos of the TGS pcb with the type caps you've suggested .
Hmmmmm makes me think if this is the answer to my problem .
I 've also made another set of coils as Max suggested ( 25DD as described and build in the PDF Ivconic made) : 6 - and 6.5 mH , aprox 22 ohm , shielded with airgap , used the correct type of cable and managed to get 14,5 khz on both sets of coils .
The problem remained : very low detection hight ... so I've ordered new caps of the type you've suggested and I'll cross my fingers when replacing them .

regards Danny

[Dennis the Mennis]

It is unlikely that the low sensitivity is caused by using ceramic capacitors throughout the design. Polyester caps would be preferred in the TX and RX circuits, but not essential. Ceramic caps are best for coupling, decoupling and filtering. If you change the TX and RX caps for polyester types, I doubt you will notice any difference.

Please define what you mean by "low sensitivity". Presumably you are referring to detection distance?

Hi Qiaozhi ,

Thanks for your reply ,

Yes I was referring to the detection distance , I am reading this thread for many weeks and collected all data I thought was necessary before I've started my project hoping I would reach the Finish without any help .
So I'm lost somewhere down the track but I don't know which way to the finish .
I will change the 'cheap' ceramics and I'll see what will happen.

I've managed to get all scoop signals as posted on page 57 by Max ( also collected in the PDF file ' TGS1 Compare.pdf ' ) , this could be also very usefull for the others started this project.
I am still focussing on the 'all metal' mode for starters.

I've also made another set of coils matching also the required specs but the problem remains , so I don't know if I can exclude the coils as the possible problem.

My puzzle continuous...

regards Danny

[Qiaozhi]

The problem remained : very low detection hight ... so I've ordered new caps of the type you've suggested and I'll cross my fingers when replacing them .

regards Danny

What detection depth are you currently seeing for various targets?

[Dennis the Mennis]

I dont leave it for a detector from a shop, i made two detectors ( delta-pulse and Garys PI detector ) and works good.... i will try it again from the scratch with new pcb with the same parts, I know TGSL is a good detector.

Hi George W ,

perhaps a stupid question : but what happens if you remove the 358 ( ic 107 ), this one should trigger the alarm / speaker .
possibly this way you can locate the problem ...

regards Danny

[Dennis the Mennis]

What detection depth are you currently seeing for various targets?

Hi Qiaozhi ,

Thanks for your reply ,

At this time on a 2 euro coin about 25 centimeter and on a 1 euro I think about 15 - 20 cm or worse .
My wifes (flat)iron 30 cm hahaha.
The only thing I've 'discovered' on sight was the difference in caps used: that's why my first question was posted .
I hope I get some performance improvement there.

The nulling of the coils is in my opinion good , with a multimeter 0 mV and with the scoop aprox 60 mV directly measured on the Rx coil and I've also played with different values of nulling ( 60 -80- 100 - 120mV etc) offered to the first opamp stage due to the S/N ratio .
I've tried , I think , almost everything posted here : reversing the coil leads , put one of the coils in the other direction , correct start -end configuration , used shielded cable from the pcb to my pot meters (I thougt I've measured some small noise transmitted from the previously used cables) etc etc .
So if anyone discovers any 'desparation' in my posts ...

regards Danny

[Dennis the Mennis]

Ofcourse the distances are measured in air.

[GeorgeGW]

Dennis i replaced the opamp.. but nothing..... i construct a new one!!!

ivconic: new pics!!! i will buy new components as soon as possible!!! thanks!!!