Problem with TGSL EDU

[satdaveuk]

Hi
Is your ground balance working? also where are you checking your kit? Take it all outside, adjust controls midway, all metal, then lf still a problem back sense off.

Let us know how you get on

[knutdi]

Ground balance is working good, i was check my kit inside and outside with the same problem, i was test adjusting all controls and the problem persist, i was change 2 circuit TL071( That came with the kit ) with 2 circuit LM308 ( It came with Serigraph on TGSL EDU board ), and change too 2 2n2222, because in my first assembly i install them wrong, and when placed correctly again began to take the problem I have.
thank you for your help, but do not know what else to try.

[hugo]

@knutdi :

It sounds like a GEB trouble.
With all pots set to zero (GEB & DISC), what is your phase angle between TX and RX signals ?

If needed, restart from the beginning.
Check TX freq., null coil adjustment, phase angle and tank capacitor on RX coil (20° for a DD coil).
You have to adjust the RX cap. very carefully (by 1nF step or even less).

Can you measuring resistance of TX and RX??

Sorry, My TGSL is running with a Minelab coil.

[eduardo1979]

I've never had this problem. You have to replace the plastic box with a metal and the potentiometers and the coil connector must be connected to the metal box. No need to use TL071. Use LM308. Change 22uF capacitors. Use 2x10uF in series. (C14 and C17). I think you have also problems with the ground balance. You must refuse the ferrite. Use LM7808 or 2930 (8V) for the voltage stabilizer. Canceled the coil to 4.7 mV. With all that you need not have any problems.

[knutdi]

@knutdi :

It sounds like a GEB trouble.
With all pots set to zero (GEB & DISC), what is your phase angle between TX and RX signals ?

If needed, restart from the beginning.
Check TX freq., null coil adjustment, phase angle and tank capacitor on RX coil (20° for a DD coil).
You have to adjust the RX cap. very carefully (by 1nF step or even less).

Sorry, My TGSL is running with a Minelab coil.

Hi Hugo, I haven´t got oscilloscope to measure everything you coments, I only have multi tester.

Where I can find how to make the coil Minelab???

[knutdi]

I've never had this problem. You have to replace the plastic box with a metal and the potentiometers and the coil connector must be connected to the metal box. No need to use TL071. Use LM308. Change 22uF capacitors. Use 2x10uF in series. (C14 and C17). I think you have also problems with the ground balance. You must refuse the ferrite. Use LM7808 or 2930 (8V) for the voltage stabilizer. Canceled the coil to 4.7 mV. With all that you need not have any problems.

Hi Eduardo1979, I'll try to put all in a metal box, I'm using 7808 and 2x10uF in C14 and C17.
How can I canceled the coil to 4.7mV????

[eduardo1979]

The coil must cancel as much as possible for best results. My coil is 4.7 mV for annulment and doing very well. Try to put the PCB in a metal box and connect everything to the ground (GND).

[hugo]

@knutdi :

Where I can find how to make the coil Minelab???

I've got a commercial coil (TS1000), not a DIY one.
Yours should be ok, you just have to adjust it well.

It will be easier for you if you can work with a scope.
See here for a PC scope : http://www.geotech1.com/forums/showp...&postcount=869
and here : http://www.geotech1.com/forums/showp...&postcount=870

[simonbaker]

Hi Eduardo1979, I'll try to put all in a metal box, I'm using 7808 and 2x10uF in C14 and C17.
How can I canceled the coil to 4.7mV????

Hi knutdi:

I hope you connected those capacitors in series with opposite polarities! (not in parallel)

Also you should replace the 1Meg feedback resistors (R31, R29) on the LM358 U103 with 470K instead.

Then this may sound weird, but turn off the lights and try testing again.

-SB

[eduardo1979]

I've never had this problem. You have to replace the plastic box with a metal and the potentiometers and the coil connector must be connected to the metal box. No need to use TL071. Use LM308. Change 22uF capacitors. Use 2x10uF in series. (C14 and C17). I think you have also problems with the ground balance. You must refuse the ferrite. Use LM7808 or 2930 (8V) for the voltage stabilizer. Canceled the coil to 4.7 mV. With all that you need not have any problems.

Change 22uF capacitors. Use 2x10uF in series.(C14 and C17).
10+10 in series = 5uF. Regards

[knutdi]

Hi knutdi:

I hope you connected those capacitors in series with opposite polarities! (not in parallel)

Also you should replace the 1Meg feedback resistors (R31, R29) on the LM358 U103 with 470K instead.

Then this may sound weird, but turn off the lights and try testing again.

-SB

Hi simonbaker, yes , i have connected 2 capacitors 10uF in series with opposite polarities.
I will buy LM358 resistances to change and I hope that the problem is that I'm eager to get my TGSL.
I tried to turn off the lights and the problem persist.

[knutdi]

@knutdi :
I've got a commercial coil (TS1000), not a DIY one.
Yours should be ok, you just have to adjust it well.

It will be easier for you if you can work with a scope.
See here for a PC scope : http://www.geotech1.com/forums/showp...&postcount=869
and here : http://www.geotech1.com/forums/showp...&postcount=870

Thanks Hugo, I look to try to get myself a scope

[knutdi]

Hi knutdi:

I hope you connected those capacitors in series with opposite polarities! (not in parallel)

Also you should replace the 1Meg feedback resistors (R31, R29) on the LM358 U103 with 470K instead.

Then this may sound weird, but turn off the lights and try testing again.

-SB

Hi simonbaker, I changed the LM358 feedback resistors for 470k and has improved a lot, I think the problem comes from there, what happens is that it has now lost much distance detection, and did not detect materials such as gold

[simonbaker]

Hi simonbaker, I changed the LM358 feedback resistors for 470k and has improved a lot, I think the problem comes from there, what happens is that it has now lost much distance detection, and did not detect materials such as gold

It's tough, sometimes a particular coil or PCB has problems and you build another and it is better. We should be able to find what is wrong, but I have studied two MDs side by side and it is very difficult sometimes to understand why one gets better depth or has less noise, etc.

Have you tried taking your MD outside far from any electrical noise?

If the RX resonant frequency is too near the TX frequency, it can cause many problems with gain and discrimination.

What happens if you put the Sensitivity pot to max, how does that affect the depth and chatter?

-SB

[Qiaozhi]

It's tough, sometimes a particular coil or PCB has problems and you build another and it is better. We should be able to find what is wrong, but I have studied two MDs side by side and it is very difficult sometimes to understand why one gets better depth or has less noise, etc.

Try comparing the TX and RX signals from the two coils. How do they differ regarding the residual voltage and phase-offsets ... and how do the RX signals react when ferrous and/or non-ferrous targets are placed near the coil. Also, is the electrostatic shielding the same on both coils?