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I need a bit of help, please


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So, I have this new-to-me GP3500 and several coils... but I am having problems getting it to sound off properly.

This may get a bit long, so i'll put it into sections: :grr01:

I have the coil cable velcro'd straight up on the shaft, coiling tightly only on the upper half. I have velcro holding on to the coiled area, too, in an effort to both keep the cable still and align the plug to go in the connector.

My settings are:

Tracking, Medium speed, Mono, and normal for the others. Volume, Tone and Signal are all about middle of the sweep. I always Auto Tune when I fire it up.

The stinking On/Off/Threshold is pestering the crap out of me, so I've begun using the switch on my L-ion battery (which loses the tuning, I've noticed)

I have a Detacc amp, also

I have been using the external speaker, but will switch to headphones for further testing. I can see my head splitting already, though, from the constant falsing. :head:

I am primarily using a 9x14 NF Mono coil, but have the problem on all the coils I've tried (16" round NF Mono, 6x10 NF mono)

I Get over a small test sample and notice that I cannot get it to sound off well at all. Compared to Sgt Frank's modded 2000, you'd think I had the coil 15" off the target. I've tried fiddling with the settings and cannot get it to be either crisp or loud right on top of the target at any point through the coil's area.

I turn the threshold up enough that I can hear it above the electrical hum (get that even with the amp volume and other stuff all the way down) and I can't seem to get the dang thing balanced. I am using the green button. It goes wee on the way down and woo on the way up. It's not a large variation, but it is noticeable. Also, the threshold just seems chattery and unstable. I can be sitting still and it will just jump around a bit. The same thing happens in Fixed tracking, too. :hmmmmm:

I've been nowhere near any sources of interference when this happens.

I don't have any skid plates on the coils, so there's no trash (or dimes) to be worried about. If I so much as think about scuffing the coil or, God forbid, bump the dang things it rings out LOUDLY like an overload. :yikes:

I have noticed that wiggling the connectors on the coils will also cause falsing.

I've watched both the Jonathan Porter and Chris Gholson video series and cannot get that stable hum they demonstrate on the videos.

I am finding bits of lead and smaller-than-boot-tack sizes of iron, but those are almost all close to the surface and scream at me for the most part.

I could really use some 3500-specific help, as I've searched and searched and can't seem to find much.

Who in the Valley has a 3500 and would be willing to spend a bit of time with me to help me learn a little more about this fine piece of electronics? Does anything I've described above sound like I'm in for either sending in the box or having to buy new coils (they are all about 5 yrs old, but barely used) :barnie::fl:

Thanks in advance!

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Over the years I have found that the type of problems you describe are either, (1) loose coil connection or (2) internal damage to the coil ... Generally, my experience has been that 95% of the time I'm having problems the source is operator error (me!) ... Check the integrity of all your connections ... Cheers, Unc

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Thanks, Unc.

As for connections, I'm just shy of grabbing a monkey wrench and ranking down the connectors. I double, triple and umtiple check the connectors over and over.

I'm 99% sure it's a case of user error, which is why I'm to the point of begging for an experienced 3500 user to help out.

A couple of acronyms for you guys, from the computer industry... but could be modded for this (and many other instances)

PICNIC - Problem In Chair, Not In Computer

PEBCAK - Problem Exists Between Chair And Keyboard

kind of like the ID10T error. Or the mechanically dis-inclined 710 cap on top of your engine :) (Look at that one upside down)

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First thing Glenn disconnect ALL the after market stuff......before you connect the coil to the box gently try to move

the box connector where the coil connects....

It's unlikely that all three of your coils are bad....especially since their NF....but if you have a Minelab 11" Rd DD

try that also....be sure and use a Minelab GP3500 battery that's fully charged....

If after going pure Minelab with ALL the accessories disconnected and the problem is cured...HURRAY...then add

the accessories one at a time until you find the trouble maker....

If none of the above works call Minelab repair and get a repair number....OR take Sgt. Frank on another 35mph

quad ride and check out his heart....half way through the "ride" he may just give you his detector if you let him


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Don I must say Glenn did very well on our Sat trip. Nice and easy. On our first trip out with Glenns 3500 I asked how many targets he found after a couple hours. He said zero. I have a nice very small test nugget with me that my 2000 gives a nice crisp signal on. We ran Glenns 3500 over it and nothing. I told him up start checking his settings until he picked up the nugget. It was the threshhold up too high. But the response was very weak. We both had small coils. I was using headphones and Glenn a speaker. I've told him to get rid of the speaker. Say what you want about speakers but I believe you will miss faint signals with them. I must admit I was lusting after a 3500 for a second detector. Though I'm not so sure now. I with you Don. Take off all the add ons and work up from there. Glenn you can use one of my coils if you sill have the issue with everythig off just in case it comes down to a coil. I know they have no issues. I bet it's the sound amp or a bad cable

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All good thoughts Frank....especially about the speaker...just like the discriminator....both loose gold....I forgot about that

Glenn be sure the disc. is turned off too....

Frank you could also check out all his coils on your machine....don't give up on the 3500....mine is almost as quite as the


I was having some of the same problems that Glenn describes so I also disconnected my "gold screamer" end of problems....

When you call Minelab repair the first question they ask is what coil are you using....so start there....

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Once all the junk is off and back to 100% minelab including a stock 11" DD coil ... if there is still a problem check the power cable ... they had a habit of flexing themselves in to falsing hell. Before you send it to Minelab for service try a new power cable or one that you know is working well ... I believe the 4 pin power cable from any of the SD's or GP's will work on your 3500. Over tightening the connections will lead to internal problems in the control box so leave the Stilson at home. If the poer cable connector on the rear panel or the coil cable connector on the front of the control box are loose it is a trip to Chicago for the box. Call Minelab and get a repair ticket.

Mike F

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WELL, it sounds like a problem with the machine to me...very much like the problems I had for several years and visits to ML Las vegas...Glen after you try using the machine stock, have checked all your connections, tried a different power cord...then you are left with intermitent problems that will require a trip to Minelab...but, be sure to eliminate all the other varibles first, as others have suggested...these machines often work, but, like people, not to their full capacity...


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Thanks All!

I will drag it out of interference range this evening with all non-stock items removed (including the L-ion battery and HD power cord), the 11" stock coil connected, and 1g and .5g nuggets with which to test.

I'll report back the results...


Will you be around Sunday? Would like to come out and have you take a peek. I'll drag the rhino and Frank out, too. I'll bring a test nugglette as we all know there's no gold left in LSD lol

Can't do Saturday as that's my kitten girl's 6th bday party. :D

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Well, I got stuck in traffic on my 50 mile commute and didn't get home when I wanted to.

so I spent the evening cleaning everything and setting up my machine to ensure no cable movement. In doing so I realized that there are skid plates on my coils! I didn't think there were any. I can't find the roll of silk tape I got with everything, so i didn't take them off, yet. It would certainly make sense that the problem has gotten worse as I've been using the detector because I have poured dirt over the coils a couple or twenty times while digging junk targets.

I'll find that tape tonight and clean the coil bottoms.

I did make a coil connector stabilizer like I've seen in the tips and tricks forum using two nylon cable clamps and some industrial strength velcro I bought for the coil wire job. I'll get a pic this morning and post it up. I know Sgt Frank will be happy as my previous setup was not 100% to his liking :) Even though the only place I coiled the cable was on the upper shaft. Now it only coils between the bungee mount and green button handle

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Sometimes you will find alot of dirt inside the covers along with BLACK SAND thats a possibility.

And Glenn invest in a SCOOP Don't pour sand and dirt on your coils. Just pass a scoop full at a time over the coil to find the target.

Good luck with it buddy.

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Indeed just a small amount of black sand in a coil cover can drive the operator nuts and will make the detector (any detector) act stupid as it acts like a target inside the cover and every bump or quick movement will cause falsing or erratic behavior especially if running in auto tracking....

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Glenn try waving the scoop of dirt over the coil...then half goes in your hand....wave the scoop again and if the

target is still in the scoop, chunk the dirt in your hand back in the hole....if the target is in your hand, chunk the

dirt in the scoop back in the hole....half a hand full at a time in the scoop until only the target is left in the scoop...

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Glenn it's a wonder you had kids. You do everything backwards. You picked up that dirt dumping on the coil from the training videos. You start wearing those JP short shorts i will not get in the Rhino with you Monkey see monkey do. In most cases the target will sink to the scoop bottom as you shake the dirt out. Same with the coil cover. We need to go over everything on your setup. Everything! Except for the black sand in your undies.

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I pulled the covers off last night out near Bulldog Wash (5 miles from my house) and did find some dirt under there, but it didn't react to my pick magnets.

Either way, it appears I'm now able to get the threshold stabilized and it's sounding off on my .5g nuggets about 8" in an air test (which is where a pi doesn't do well from my learning)

I put the covers and coils through a thorough cleaning last night and got all the torn-to-crap tape good off (dishwasher are great! just kidding! I used good gone only on the tape and a barely damp cloth).

The covers are back on and fresh coil tape. A question now... for a spoke-style coil, how the heck do you avoid sand and such getting in through the interior sections? Only the outer perimeter was taped previously. Should I tape those areas, too?

I can certainly tell I have a lot of learning on this new to me machine. It's like learning to detect all over again coming from a GMT.

Thanks for the pointers and tips, guys!

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Ok first off Glenn the GMT was kids stuff....now your on the front porch with the big dogs.....

Did you pick up the .5 gr. nugget with ALL your coils....did you do this with out the add on after market stuff....we need

more details on your test.....

For spoked coils I use silicone on the inside of the skid plate with a contineous bead of silicone and the seal inside the

skid plate is solid and nothing gets past it....then I put PC-7 on the bottom of the skid plate for protection and so far have

never worn one out....in the rare cases when I had to remove a skid it was a bitch to get off in one piece....a kitchen butter

knife works if you go slow....

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Updating on my phone is a pain...

all stock - able to get stable and pick up the nugget with all coils (and both positions of XRP coil) at an average of 8" with covers off (those that come off - XRP is not removable and stock doesn't appear to have one

Covers cleaned up and back on - was able to get it stable and hear the nugget at same heights

Added amp back in and associated battery - After I damned near blew out my ear drums I was able to get it stable and get nugget at distance decently over a foot in the air.

there was some dirt under the coil covers, but didn't appear to react to a rare earth magnet... but does seem to have been the issue.

Will have to wait until I get back into a wash to verify all is stable in a real world test, though.

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G'Day Glenn

I've been following this post. When you initially put it up, it seemed like you pretty well covered a lot of common problems. I was going to suggest the cover plate because I've had that problem before but you said there was no cover plate so I just blew it off well out of my range.

I've only had 2 problems with mine and that's been the cover plate and loose connections. I don't over tighten, that could be my down fall. After you've been swinging for half a day, those connections tend to work themselves loose.

Good to see you've got on top of it but I would continue to work yourself back, adding on to see if the situation occurs again.



P.S. If I take a lunch break, I clean the cover out and at the end of the day, I religiously clean the entire unit down. You'd be surprised how much grit and grime get in the cams between the covers, cuffs and just basically everything gets covered in some sort of fine abrasive material. All can be detrimental to the unit in it's performance as well as deteriorating it's pristine quality if you decide to sell it and upgrade.

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Thanks, Johnno. I've added everything back on and no issues.

I, too, am religious about checking connections... and often.

By the way, here is a pic of the inside of my 9x14 NF Mono right after removal. This is the coil I seem to use most. None of this reacted to my rare earth magnet, though. So i'm still at a loss as to what the problem was.


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Reading all directions, I have a 3000 and just recieved new spoked coil sealing with silicone on inside spokes sounds great but you lost me on the PC-7 I am sure all of your help will work on my 3000 that is applicable. Thanks The Farmer NWA

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