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Offline vector180Topic starter
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« on: March 04, 2009, 06:06:35 pm »
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Hi all,
One of the guys at work here was aware of my metal detector chasing and kindly brought his old unit in...of course it doesnt work!, it looks cheap has only  a handful of components.

The handle grip is orange with a speaker and two "fine tunning" knobs.
Aluminium telescoping shaft and 6" coil plate.

Seems to have an intermittent problem.. may just be setup. I have no manuals or notion has to null or set it up..

any help would be great.

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Offline Eugene52
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« Reply #1 on: March 04, 2009, 06:32:43 pm »
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Quote:Posted by vector180
Hi all,
One of the guys at work here was aware of my metal detector chasing and kindly brought his old unit in...of course it doesnt work!, it looks cheap has only  a handful of components.

The handle grip is orange with a speaker and two "fine tunning" knobs.
Aluminium telescoping shaft and 6" coil plate.

Seems to have an intermittent problem.. may just be setup. I have no manuals or notion has to null or set it up..

any help would be great.


Hello a GC-1002 is the most inexpensive I could find . Poor solder joints are always the problem on a cheap over seas product .

Regards...........Eugene52

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Offline vector180Topic starter
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« Reply #2 on: March 04, 2009, 06:46:38 pm »
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that looks just like it Smiley
I tried the old solder all the joints trick.
Looks like I will have to trace out the circuit and see whats causing the problem.

Almost not worth worrying about but it will help me understand a few things I am sure.

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Offline Eugene52
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« Reply #3 on: March 04, 2009, 07:01:09 pm »
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Hello vector180 , You know the routine , Visual inspection 1st , look for popped capacitors and then smell for fried resistors , take voltage readings on ebc of all the cheap MPS japanese transistors , make sure you have continuity on the speaker... etc...etc...
Keep us posted ............ Great..............Eugene52


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Offline Beachcomber
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« Reply #4 on: March 05, 2009, 12:25:49 am »
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The simpler a metal detector, the easiest it is to fix... Detecting

A neighbour's kid happens to use one on the beaches here. Bought it for 19,99 euro last year.

The detector does not react on our largest coin, the two-euro one.

It does well react to toy cars, beer cans and the like.

HH

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Offline vector180Topic starter
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« Reply #5 on: March 05, 2009, 02:39:37 pm »
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Im really after a manual for this beast. Knowing how it is supposed to be balanced/nulled would help. ie the settings of the two fine tuning knobs.


I found that there were components in the coil head last night. So Im checking them now and trying to trace out the circuit.


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Offline vector180Topic starter
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« Reply #6 on: March 05, 2009, 10:15:01 pm »
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HI all
Here is the circuit (attached) of the radio shack unit.
I had a number of problems. First the Speaker, of all things, was intermittent and finally died.
However after following the circuit thru all seems to be in order.
The unit oscillates at around 133khz. Placing metal near the coil dampens the amplitude of this oscillation. A dc voltage of comes from the head via the white wire and a voltage between 1.3 and 2votls triggers the audio output.

The tuning knob is turned until a blip is heard in the speaker then the fine tuning knob can get the bips constant. By following this procedure one can null the ground interference. However this is very very touchy. Observing the heads dc output(white wire) the range is quite nice and its easy to pick metal objects effecting the coil. But the audio circuits ability to interpret this dc shift is poor. Tuning knobs can easily shift the dc above the 2v or below the 1.3 at which point all buzzing stops and you miss the shift caused by metal.

Im not sure anything is faulty with this unit(apart from the speaker I replaced) I just think its very touchy.
Analog electronics like this is not my forte. Im not sure I understand the osc head circuitry although I have checked it matches what I have drawn up.

Could be one of those devious circuits that have been reduced to the bare components.

I wouldnt mind understanding this just for future thoughts. So feel free to elaborate if you get the circuit.

cheers
Mark

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« Reply #7 on: July 10, 2009, 10:19:00 am »
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vector180;
From the voice of experience (comes this big booming voice, out of no where!) I have been hunting some  Radio Shack manuals, myself, recently, I found zillions of reference material on my HR2500 (?) 10 meter Ham radio.

Just enter the model number into the Google window and push the search button.... its easy. I even tried a BC-AR-239 which is a pre WW2 mil radio receiver.... I found it. I was looking for one to convert to transistors... can't get one now without lots of money because they are collector items.

Ive got an old Rad Shack detector, it works OK for coins just under the surface. I got a schematic, figuring I might improve the thing... faint hope!

Does anyone know anything about the mil-surplus mine detectors, the vibrating ones???

Brian AKA goldigger.


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« Reply #8 on: July 10, 2009, 01:12:32 pm »
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I have one of those old radio shack detectors my youngest son uses it while im detecting
he has found some good stuff in parks here in tennessee with it he found a 1964 washington
quarter about 3 inches down with it

bobbyc

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Offline brucewj1955
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« Reply #9 on: June 16, 2011, 01:55:18 pm »
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Sir:

Did you ever retrieve any literature... owners manual etc. related to this detector? I ask because I have 1 of 2 remaining from when my wife bought them for our kids when they were young... 15 years ago. My e-mail address is brucewj1955@yahoo.com if you might consider selling me copies of any manuals you've come across over the years.

Thanks for your time,
Bruce Jennings

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