Goldscan lV PCB

[greylourie]

I have disconnected the SAT-Mod. Now the possibility to ignore iron is much better and lacking of depth is not so much as with the SAT-Mod. But the complete GS is very noisy, you can´t seldom get a constant treshold. I have it to try it outside.

The potential for noise in this design, is mentioned by others who constructed it. The first step is to identify what elements are causing, or contributing to noise. A lot of talk centred around elements of the power supply. One definite improvement was recorded by Jose', and that was to use a 7660 as is used in the Hammerhead power supply. http://www.geotech1.com/forums/showt...074#post166074

And Max mentioned "by-pass" caps on the input and output of the 7805 regulator, to remove ripple. http://www.geotech1.com/forums/showt...5856#post75856

The particular goldscan you own is commercially produced machine and depending on the age, some parts might now be reaching the end of their working life. So whilst I would advise against adding any modifications to power supply without the approval of gurus, (especially as I have zero work experience in that regard) I don't see a problem with looking at the performance of original fitted parts that might now be a little tired with age.

I also noticed from your photo's that your board is very clean and free of flux, so that cannot be a possible cause.

How does the "Frequency" adjust help with electrical interference, when testing the machine inside your home ? Does it give an improvement in noise levels when the knob is adjusted ?

I'm sorry I can't offer more avenues of investigation for you to check in your noise problem. But previous posts by others point the finger at the power supply and its design.

Maybe someone will come along and offer some advice.

[scs]

Discrimination in PI is reality only with two coil detectors.

[mschmahl]

I tested it outside. After 1 Minute it was ok and stable. But i lost it and it kocked on a stone. Something in the power supply is now broken. I can´t get 12V from the 7912CT.
Before that, there was no noise from the power supply. It is in a extra box away from the amps. So there was not much left, which arrived the OP-Amp.

[greylourie]

I tested it outside. After 1 Minute it was ok and stable. But i lost it and it kocked on a stone. Something in the power supply is now broken. I can´t get 12V from the 7912CT.
Before that, there was no noise from the power supply. It is in a extra box away from the amps. So there was not much left, which arrived the OP-Amp.

Oh Dear !

We will have to fault-find. Do you have a multimeter ? Can you take some readings from power supply lines feeding to the main board ? Hopefully it is a dry/broken connection from the power supply harness to the main board.

[greylourie]

Here is the power supply schematic. It appears to be quite simple in design.

First we have to establish the status of your battery power pack. Is it made up of individual and disposable batteries ? Or are they rechargeable ? Can the health of the batteries be confirmed as having the required output ?

[mschmahl]

Thanks for the schematic.
My batteriepack is OK. It is 10x AA (15,75V).
+5(+4,9V); -5 (-4,99V); and -12V (-11,95V) are ok. Some of the transistors or 555´s make sound without headphones or speaker connected. Have to check this. And 7912 gets realy warm.

[greylourie]

Thanks for the schematic.
My batteriepack is OK. It is 10x AA (15,75V).
+5(+4,9V); -5 (-4,99V); and -12V (-11,95V) are ok. Some of the transistors or 555´s make sound without headphones or speaker connected. Have to check this. And 7912 gets realy warm.

The 7912 getting really warm, is this the way its supposed to be ? Your battery pack is not so large in capacity - but then I'm not an expert.

My initial thought was that possibly some connection had become dislodged or damaged, during our survey of the board and its components. With you confirming various outputs as should be, then this would be the next line of investigation. See carefully if none of the lines leading from the power/audio circuit to the main board have dry or damaged connections.

The noise issue has been mentioned by others before. A post by Max suggested some caps as added filtering. He describes it here : http://www.geotech1.com/forums/showt...5856#post75856

Jose' built a very nice machine. His solution for noise is described somewhere on the forum. He gives a hint here : http://www.geotech1.com/forums/showt...612#post162612

But what you need to decide is.... do you really want to do anything so drastic as change your supply from the original design ?

That is a very big step, especially if the one you have was made originally by Eric Foster himself. I expect those are as rare as hens teeth, compared to the ones produced by Pulse Power.

[greylourie]

Looking at a photo I found in other thread, you can see the 12V regulator fitted with a clip-on heat-sink. This would imply that some heat energy is generated and needs to be dissipated during the course of normal operation. I expect that is the normal case with regulators of this type.

If you are really keen and want to experiment with the option that Jose' implemented. Then maybe you could look at building a small circuit on strip-board, and carefully substitute the original.

[greylourie]

By taking 12V from your original supply or building it into your substitute, and feeding it to a circuit clone of the Hammerhead supply you could, possibly, end up with a quiet solution. Deactivating your original and connecting in the substitute would take some careful tracing of your circuit board. You would need to tread very carefully and double check any connection needed for audio. Also bear in mind the need to supply pin 7 of IC1 (HH PS), with a filtered/regulated signal from your GS TX 555 ic. Obviously IC4 is excess and not needed for your board.

Personally I would look at trying suggestions made by Max, and which I gave a link to in post #76. It can easily be reversed if it proves to be unsuccessful, with minimal impact to your original.
Unlike Jose's solution, you would not have to de-solder or remove original parts.

Looking forward to seeing how this noise problem solved.

[greylourie]

Hello mschmahl,

Did you ever cure your Goldscan, after the bump on rocks ? Just curious.

[mschmahl]

Hi greylourie!
No i have it not repaired it till now. But you are right, have to do it. But so much other projects. I think the problem is around the coil/dumping. A bad solder connection. If i switch to the inbuild pinpoint-probe all is working.

[greylourie]

That is positive news. That the pinpoint probe works, shows that questioning the power supply was a red herring. Good, hope you get it running some time.

[mschmahl]

The Goldscan is working now. There was a problem with the Coil-Connector/ Coil-Switch/ Dumping -sektion. I have solder all new. Now the GS is working.
Does anyone use a orginal Goldscan and can share some settings? I have only this 2 sites of manual.

[greylourie]

Manual Page 2

Here is the other page.

[mschmahl]

Thank´s a lot.