LOOKING FOR GOLDSCAN 4 Schematic.

[porkluvr]

I will add this: So long as 470k or some other reasonably low R value (a value not in the high MΩ range) is added
to IC2-3 and IC2-5, guard rings (guards) are unnecessary because the opamp inputs no longer have a "very" high impedance.

Guards will only have noticeable effect on ability to maintain any charge on the 470nF capacitors when the opamp input impedance is very high.

I redrew part of the original drawing, to add the -usual- 470k resistor and also to try and clarify how the guard would be, if it were used (which isn't necessary, with 470k resistance). Not shown, is that the guard would probably get connected to the nearby -input of the opamp (pin-6, here) but I would need to see the original board to know for sure.

But, the bottom line is: don't need it, so don't worry about it.

The exact value of the "470k" is optional, but for both channels to track each other the R vales should be the same in each channel.

[petoco]

Hi Jose!
Gracias thanks for your explanation, now I get it how RV2 works, the problem is that I ve an oscilloscope that is a relic from 1967 and no works very good and the accuracy is poor.
I manage to solve the Gnd for coil , ne5534 and capacitor thanks to Porkluvr tips and no lost the -12V but the coil seems not working I will check the IRF740 no voltage dropp between drain and gnd,,

Thanks friends i really apreciate your posts!

[Jose]

Hello Petoco
RV2 sets the minimum time delay "delay" through the 50K pot.
For example, in some commercial detectors, the minimum time delay is 10 us. This depends, among other factors:
The forward amplifier design.
The design of the coil.
The TX power.
In my GS4 minimum time delay could be achieved is 13 to 14 us, then adjust RV2 for a minimum time of 12 us for not moving to a shorter time for him only increased noise in the detection.
Hope this helps.
regards

[petoco]

Hi porkluvr,
Thanks for your quick reply, I follow the Papa alex drawing that you refer to, and taking the other schematic where the R49 and R50 are modified and put to ground fets and applying some other tips covered here, As you said I think the problem is in the coil circuitry and I will check it the path and comonents due to I made my own hand made pcb boards separate each other and probabliy there is the problem.

For the other questions in the case of RV2, dont see nothing related to how to calibrate it, and for the ring guard I read it on Thread STATE OF ART GOLDSCAN IV on post 4 where alex mentioned the gnd caution that you clarified to me as well the ring guard is mentioned and you can see it on Papa Alex drawing, but in the same post he said is not a critical stuff for the proper working of the circuit.

Again thanks for your tips friend!

Alberto

[porkluvr]

Alberto, what the "Caution" is telling you is that you should have the coil return (coil ground) and the + terminal of the 3300uF very close together, connected with a wide PCB trace. This trace forms the hub, or center point, of a local ground which connects the ground terminals of the other components where the dashed line touches.

This local ground should then get connected to the power supply ground and all the other ground connections in the circuit. It's the same idea as having a separate analog ground and a digital ground being connected at a single point in a digital system such as an A/D converter. The idea being, you need the separate grounds connected, but connected at only one point. This helps prevent noise getting into sensitive circuitry.

If, by connecting the local coil ground to the main ground, the 7912 output then becomes -8V, that is a serious problem. I think something may be shorted on your PCB; either a bad component, a shorted trace, or else you may be misinterpreting the drawing and connecting something that should not be connected.

Now, that's easy enough... but your other two questions may be a little harder to answer.

It would be easier to answer your questions if you would give a reference to the post# where you found the schematic you are asking about. There is the original Papa Alex's drawing in post #4 but that cannot be the same as what you referred to. So, where?

[petoco]

Hi every one! I have been follow this forum for a while,, I find pretty interesting and well preparate people with very good electronic skills , a made a couple of little projects following this forums, and I have been trying the goldscan Iv for a week and after collect all the components realize of two things that I cant really understand and maybe is the reason of problems,
In the schematic the CAUTION same junction GND point at coil o C46 wath is this, I figure out the inner of the dash line is a separate gnd by their own, and with no conection of the gnd of power supply part, that is share with the rest of schematic,, but in that way,, and logically the coil is not feed, and if I connect the caution GND to the same gnd of power supply and the rest of circuit the -12V drops to -8V. In a few words, if any one is very kind and explain how to make this gnd caution connection I will appreciate.

Other question to follow the line,, would be the ring guard en pin 3 de U12??.
How to adjust the RV2, are there any tip for taht

Thanks for all of you, and always do the right thing!!

Alberto

[Jose]

ABDW9
If heated 7905, is an indication that there is excessive current draw may be a damaged component or improperly installed, some short tracks on the pcb, look for the cause.
The Hold function, it is difficult to understand if you are not used to this type of machine.
Reg explains this in post # 157.
The combination R51 and C34 adds a small delay turning and turning off the FET that are there to eliminate the opposite half of the signal. In this case, a negative signal is normal and when the signal goes positive U12B, the FET is determined by the setting active RV4. If this step is inhibited by activation of the switch, the audio heard would be a wee / woo if the threshold is high enough. This is the most common sign that you hear on the other IP.
Jose

[ABDW9]

Hello again,Today you turn the device after a long period I stayed assemble componentsHere is what has reached and some observations, which can help you put your opinionsFirst dabble device and this after noticing the audio output of the BezzoBut these remarks to see what your comments and what can I do to the best of performance:* The sound that comes out of the Bezzo weak* There is no output on HP (peg ear)* 7905 heats up a lot and also 7912* Alresit key does not work why?* As I'd like to know what the function of the key HOLD?Thank you my brothers honoredYou all greetings

[ABDW9]

Thank you Jose
Of course people need help in urgent you
As you can see I am a novice in electronics and I have a problem in the Arabization English nor Ajidha the completely
Malk was having some difficulties in understanding the previous publications
You can help me overcome the mistakes

[Jose]

ABDW9, I do not have an original GS4 for compare results.
My GS4 done at home with common components as shown in the diagram.
I make minor changes such as the replacement of the 555 in the 7660 font that is easier and less noisy.
Good operation not only depends on the components used, but also the design of the PCB, the Bobina and proper fit.
The polarity of the source positive, is connected to GND. Respect the scheme.
There are some errors in the schemes, if in doubt, try to help.
Greetings.

[ABDW9]

Thank you my brother Jose Thank you for your interest to my questions
But I want to know I am If you connect the circuit as contained in the Catalog device works as original or shortly Ethel lack of efficiency of commercial components??
Second: I found in another site someone mentioned that income inverse voltage here means positive with the negative and positive with negative Is this true brother??
Thank you and all of the response ...

[Jose]

Hello ABDW9
The LM7912 regulator should be.
The project GS4 works well, the results mentioned in the 169 post.
It's not an easy project, takes time to develop.
Regards, Jose

[ABDW9]

Hello again,
I want you very Another Hbia necessary
Kept me only last thing I did not find it
It Rigiulietr LM7912 just found LM7915 Can I use it instead of it
You all my love and greetings
As I want to make sure if you completed the device and try it
What results do you have?
Brother Abdel Razek from Sudan
As if he wanted any of you to help me more, this Emily
[email protected]
Thank you all

[Jose]

OFF, all metal
GND, PI detector with ground balance
SEL 1, Rejects pieces of iron nails.
SEL 2, To detect certain types of English money, and still reject some iron.
Jose

[ABDW9]

respect

Hello and very sorry refer you back
Something good catches did not want to explain please
In the circle above sw1a & sw1b & sw1c Please clarify what is a task both sel1 and sel2


And thank you