PI Fig. 8 Coil for Bench Testing????

[Mechanic]

HI Carl,

If not enough current is put into the coil, the 180v cap will not reach the 180v and this will in turn prevent the front end fet cct from operating. It might work, it might not work.

Bill,

That part is a diode, it used to be a byv 28-200, it is most likely now an murs320.
If you are able to hook the scope ground up to pin 5 of the coil plug, this is detector ground. The yellow wire is the receive ground(linked in the coil plug on the coil side)
The blue is the receive wire, pin 4 is the transmit wire.

You can use a normal coil for the testing at this stage, just don't bother listening to the audio. Even later on we can use the normal coil to test that the target response is making it through to the final stage before the micro by using the scope.

Cheers Mick

[BillNEWAST]

Here are some coil inductance calculators I located.
The first is an entire multipage site on theory & more importantly
free OpenOffice Calc VB Scripts to copy/past or download.
This Guy has done Extensive research into coils and Inductance.
It's VERY Easy to follow his code and it's well commented also.

http://electronbunker.ca/CalcMethods1c.html

This one below is an online Electronics Theory Encylopedia that could prove helpful
to us all.
It has over 50 links to coil calculators of All Types and Flavors.
I haven't used or gone to any of them so I can't comment on their usefulness.


http://educypedia.karadimov.info/ele...latorcoils.htm

Mick I'll be posting pics later today, apx 5-6 pacific time hopefully, for the Scope shots.
Sincerely
Bill Adams

[BillNEWAST]

Mick, when I hooked up the 11" DD coil and turned the machine on and used a 3/8 socket and 6" extension the detector worked just fine. It was able to detect the metal from 14-16" away.
When I changed to the 250mm coiltek it responded just like a dream. Of course there was 60Hz noise but both the coils responded properly.

I think that there is some wire or screw or something that is killing the transmit or receive signal to the case or something??? I think that it may be the small Blue wire that grounds the Case on the power/batt side. You know the one that physically supports the big FET to the Case while keeping it isolated.

Is the foil on the end caps used to supply a Ground through the AL Case for the swithches and/or preform faraday shielding to the componets inside?

The following are pics of the Scope and the coil endcap. I don't know if I set the scope up right as I haven't messed with it for over 12years.
When I tried to get the wave to change when I passed the metal over the coil it seemed to not change even when I changed coils and timing on the scope.

[Mechanic]

HI Bill,

Ok, well if that is the case, then the irf730 is most likely shorting to the case somehow. Check that the little insulator is keeping the back of the fet off the case and check the screw insulator is not damaged where it goes through the hole. Also check that the legs are not getting ready to break off the fet. The other thing worth looking at if you have no joy with the fet would be the mylar strips that connect the 2 boards together. Fold the boards over how they would be sitting in the case and re-test, bump the strips about a little bit. If the strips are at fault you can buy new ones form element 14 but only if you really need to as they are a pain to replace.

The foil on the end caps is there fro electro static shielding. You need this in particular on the coil endcap to drain charge that would otherwise build up in the coil plug housing that would cause a false noise whenever it was touched or whenever enough charge built up to jump across to one of the coil pins, resulting in a lightening strike response.

Cheers Mick

[BillNEWAST]

Mick, I have made a fig 8 coil and it reads .297mH and 0.5 ohms and am posting a pic of it on the form.
The form is laid out from a 24" UFO coil. it is 24" x 12". When I wraped the coil pattern with 18 awg Speaker Wire(had to unzip it first) 19 times it read a little over .5ohms and .358 mH, so I took one wrap off and it brought it down to .324 mH. When I gave it a flip it lost mH's down to .278 mH. So I shortened the length by a couple of inches and it raised it back up to .297 mH.
I think that the coil will gain in mH by making it a more perfect fig. 8, ie both coils being more rounded than elongated. the coil would nead more wraps to make it longer and narrower, than short and fat and keep the same .300 mH.

I need to know where to hook the two wires up to on the coil plug, 1 2 4 5??? and can this be done on the test pins??

here is a pic of the 24" coil form and 23" fig 8 coil. I choose the 24" eliptical form because it has the Same circumfence length as the 18" circle, and I can make a 3ft coil or add a 14" extension for a 4ft'er, to mount on a sled/plastic sheet/blanket.



Sincerely
Bill Adams

[Mechanic]

HI Bill,

The coil ground wire(coax shielding) is connected up to pins 1 and 5. The coil tx is connected to pins 2 3 4. Just bridge them on the back of the coil plug(coil side).

Cheers Mick

[BillNEWAST]

Mick, sorry for being such a Dunce, but I don't have a Shield/ground on the coil. It only has the Begining and Ending wraps on the coil.
Do I hook up one end to the 1-5 grnd and the other end to the 2-3-4 pins?
Or do I hook up the one end of the coil to the pin 4 (white) TX and the other end to pin 2 (blue) RX????
Sorry for being so Dense, but I don't want to short the Beaste out when I have it working.
I would like to do some tests on the TX and RX sides and the Power Input side, to see what the componets are and maybe start me a schematic of the critter.
I don't have to have it assembled till Late May or early June when I'm going back in on the 1904 Briggs Pocket (2000 ozs in two weeks). I found it last year on my Scouting trip, but didn't have the Big Machines to hunt for the leftover specie, downhill (apx 55-60 deg slope), and 800 ft +++ to bottom of canyon. I tried to find the CAMP that was talked about in the 1904 Mining Report, but couldn't find it or any evidence of the trail into the pocket either, I had to BushWhack for over a mile to get in to it.
Well enough of that or I'll be tipping some of the Lookie Louiers off as to it's whereabouts.
This comming Winter I'll be making a Video/DVD of what I had to do to find it, and my Research Methods, plus the video footage from last year I took. But needed to have the Money Shots to sell it with.
I have 4 more LOST Mines/Pockets in SW Oregon I'll be hunting for also, One is the Lost Sheifflin Mine at the head of Days Creek, and a couple of others that are only known locally.

Sincerely
Bill Adams

[multieagle]

Mighty interesting story, the Briggs discovery.

Let us know how you make you.

[Mechanic]

HI Bill,

Ok well if you aren't using shielding or coax, then just hook one end of the coil to pins 1 and 5 and the other end to 2, 3 and 4.

Another thing I do when testing for internal noise improvements upon repairs / modifications is hook up a coil and disconnect the blue receive wire and hook it up to the yellow ground wire at the back of the plug. Then the output noise can be measured at the test points on the second board at the output of the filters. From the edge of the board(the second board at the end of the filter sections) the test points are as follows. Ground(ground clip to here), discrimination channel, channel 2, ground balance channel, and channel 1 closest to the middle of the board.(I may have ch1 and 2 mixed up!) Then I set the scope to 5mv/div and .5 to 1 second / div. Then take note of the noise peaks and their amplitude. Reduce this noise and the machine runs quieter.

As for tracing it out, well I hope you have a hell of a lot of patience and at least a spare 300 hours! There are 880 pins and 282 components on the main board and 853 pins and 250 components on the audio board

Cheers Mick

Ps yours is a 2200 v2 so the parts/pin counts will be different!

[BillNEWAST]

Thank You so very much Mick. On the V2 Pin 3 isn't connected only pins 1-5 an 2-4. I was worried that the wrong connection at the coil end would stuff something.
I couldn't find the trim pots you refered to in post #10 as referenced in my pic in post #14 and the closeup in post #18. I think that the microprosser in the SD2200V2
changed the componet count and was able to use fewer parts or at least change out some analogue ones for digital ones. I don't think that I'm experienced enough in electronics to take on the Whole Two PC boards.
I just want to be able to identetify the major parts/sections of the boards. You have helped by telling me that the Second Boards function is to process the Audio. You were right on the Diode. in the first pic.

Sincerely
Bill Adams

[Mechanic]

Hi Bill,
In the sd2000 pins 1 and 5 were bridged in the detector and pins 4 and 3 were linked in the detector pin 2 is receive.
Now that they have stopped using 2 pins for tx and ground the pins are linked inside the coil plug. Pop one of your mono coil plugs off and see. A dd coil is different in that pin 2 is not linked to 3&4 as it is the DD receive coil. In a mono coil the tx coil is also the receive coil, hence why 2,3&4 get linked(well you could actually leave pin 3 out as it is not connected in the detector).

Here's a piccy with the test points and the main board sections marked out....

Cheers Mick

Ps also forgot to mark the trimmers. The trimmers are above where I have written "integrators" They are for earth field cancellation, don't fiddle with them unless you have verified that you really need to.

[BillNEWAST]

Thank You so Very Much Mick, This is what I have needed to be able to begin to understand this board. Do you know anyone who needs to have an old garrett ads replacemant board, I have one thats got PN99358
761130C on it. Could take a pic of componet and solder side and post in PhotoBucket and give you the link. I thought that someone in OZ was asking asking for one a few years back and I just ran across this in my JUNK/STUFF BOX.
Again thank you Mick and have a G'Day.
Sincerely
Bill Adams

[BillNEWAST]

Mick I think I have found the problem with the V2. When I originally put the machine back togeather last year, I replaced the Silicon/White Grease with a LOT of Arctic Silver 5 on Both Sides of the small teflon insulator pad that goes between the IRF710 fet and the Case. When I checked to see if this stuff was electricialy conductive it said No on the package. But when I went to the website this is what I found.

Arctic Silver 5
Made With 99.9% Pure Silver:
Not Electrically Conductive:
Arctic Silver 5 was formulated to conduct heat, not electricity.
(While much safer than electrically conductive silver and copper greases,
Arctic Silver 5 should be kept away from electrical traces, pins, and leads.
While it is not electrically conductive, the compound is very slightly
capacitive and could potentially cause problems if it bridges two close-
proximity electrical paths.)
http://www.arcticsilver.com/as5.htm

SO what do you think???

Has anyone used this stuff before???

I'll be replacing it on the fet with some White Silicone grease that I know works.

Sincerely
Bill Adams

[Mechanic]

Hi Bill,

Don't worry about using any sort of heat conductive grease. The fet on the 2200 puts out very little heat. Just the rubber insulating pad will be more than sufficient.

Cheers Mick

[BillNEWAST]

Well here is my procedure and thought processes on how to build a Fig. 8 bench coil.

for the Minelabs we have TWO of the three variables to start the coil winding process.

1. 300uH inductance
2. 0.5 ohms

so I look up the wire sizes to find out what wire sizes will give me .5 ohms with a apx 18" coil dia.

Then I find the coil winding calculators in the first 5 posts.

In the interactive coil calcualtors enter in the 300uH and .5 ohms and give a dia. of 18" and see what comes up.

make any adjustments needed to get a winding Inductance of apx. 40-50uH over. ie 350uH @ 0.5 ohms.

What happens is that when you take coil and fold it into a fig. 8 you reduce the coils inductance by about 50-60uH.

Now this is for the 24" x 12" eliptical coil that is shown on the form in reply 20.

The reason I chose the 24" eliptical coil form is it has the same circumfance (almost) length as the 18" dia coil.

And I can use the rest of the board to make a 36" x 12" coil also.

When I got the coil in the pic wraped togeather with packing tape and took it off the form and twisted it, into the fig 8 it

Dropped to 296uH so I started to play with it by making it shorter inside the pegs and it raised the inductance back up to

310uH. And All the time maintaining the 0.5 ohms.

What I plan on doing is wraping tinfoil around it for a faraday shield and tieing it on with thread, this is so I can take it back off

easy if it doesn't work the way I want it to. Or it does something unexpected like. I was thinking of usein Duct Tape and wraping

it around the coil with the Sticky side out and laping 1/8-1/4", then using tinfoil to wrap around the stick side and form the faraday

shield.
BUT, there is NO reason to have a faraday shield on the coil because it won't be used outside next to the ground or wet grass and

It won't be moving on the bench(actually on a box on the floor like Woody's).

When I get mine made up I'm going to HOT Glue it to a peice of Cardboard for easier storage on edge, then it'll keep the same

Inductance all the time.

IF anyone has any thoughts or ideas just jump in, I know I got sidetracked off the Main topic with Mick, but had to strike while the

Iron was hot on getting my detector fixed.

Sincerely
Bill Adams