My Trusty EQ11 Coil Is Faulty, Any Suggestions?

[CliveHamy]

Hi Folks, Looking for advice and thought that the symptoms of this fault could be useful for others. I've had my NOX800 with it's 11" Coil since they first came out. Today I've realised the coil is faulty. Instead of giving the numbers I would expect for specific targets the VID's are about half the ones I would expect. For instance my spade which normally reads 17 comes in at 7, whilst an old victorian penny that should give a 23 or 24, comes in at about 11 or 12. (Field2 standard settings) I've tried factory reset and other modes.

As you can imagine this has undermined my faith in what is going on, and the readings/tones I'm getting. I've system tested the coil and confirmed that it is as fault by swapping coils with a mate and his coil gives the correct readings on my machine/control unit. I can't tell what has gone wrong, twiddling  the cable junction on the coil does not create any faults so my guess is that either a chip in the coil is faulty, or perhaps somehow less power is being generated by the coil. The machine & coil is old so doesn't owe me anything. This combo did help me co-find the Okehampton hoard of hammerds (I'll do a post for the forum sometime soon), so it would be nice to keep it going.

I'm thinking that maybe I bite the bullet and finally get a manticore, but before I folk out alota dosh, my questions are:-

1) Is this repairable, i.e. has anyone else had these symptoms? (The machine still works, so unless you knew what signals it should give this could pass unnoticed)

2) It looks like a new EQ11 coil is about £250, and there are not a lot of 2nd hand ones around, would it be better performance-wise to buy a new coltek coil say the 14x9 or the 10x5. I detect mainly Devon (England ) pasture. Which would be better, do these give better performance than the EQ11 - Hopefully i'll end up with a better machine.

Or would you bite the bullett and go for the Mantibeast?

Cheers

Clive 

 

[Airtemisa]

If you detect beaches, go for a Manticore. I will go for a Manticore, and I went for it. If you detect other sites, it depends on your budget.

Main "fault" for the Manty is the battery, consider it. 

[TTT2866]

Unfortunately this is not repairable. You can call Minelab repairs and see if it's covered under warranty - but it sounds like your machine is pretty old, so likely not. 

 

The Coiltek 10x5 is a pretty good alternative, but after using my Manticore it feels like it already has a 10x5 built in. I'd highly recommend the upgrade. 

[PimentoUK]

It may be repairable, it just depends on the fault location.

Skipping the details:

There are two signals coming from the coil, a complementary pair. One goes up when the other goes down. If one is missing, the detector still appears to function , but will give lower sensitivity, particularly to low conductors ( low ID number targets ), and will give lower than normal ID values.

Missing signals are normally caused by a broken wire, they are quite thin and fragile. If the break is in/near the coil connector, it's possible to fit a new connector. If it's in the cable , typically just near the top of the strain-relief gland on the coil, it may be repairable, though it's fiddly, and clearly water-tightness is 'lost'. But ... it can be a really low break, inside the coil, in which case it's unrealistic to fix.

Telescopic shafts seem to be bad for flexing the cable close to the coil, and causing these issues.

The good news, maybe:

I'm in the UK, and have had a go at a few of these failures now. With some successes, and a failure.

Do you have 'tech skills' , and an electricians multimeter? It may help pin down the fault if you can test a few things first, then repairs can be better considered.

If it turned out to be unrepairable, I would still be interested in the coil, and could offer you a modest amount for it.

 

[CliveHamy]

Hi PimentoUK, I'm grateful for your feedback. Your description of the fault matches what I am seeing. I've checked the coil operation in the modes of Park 1, Park 2, Field 1 & Field 2, with some known targets and all the ID's are significantly lower than they should be, but even more so in the Park2 and Field 2 modes, which perhaps mirrors your comments about low conductors. Maybe we can get some insight into the design of the coil and control unit, in the same way that different brain damage gives clues as to how the human brain works!

It's an old coil, I don't have a telescopic shaft, and rarely change it, but It is more likely to be the cable near the gland as you suggest. I have some electrical skills inc multimeter, but wary of cutting open the cable as the wires are so thin without knowing exactly how to test and fix it. If you could give me some suggestions on how to test this that would be great. I assume that I could test for the faulty wire by using some fine mutlimeter probes (will paper clips do?) into the end of the connector and test for resistivity across different contacts to isolate the fault and then maybe try and open up the strain relief gland and test from there. Any idea what each of the 7 connections do and which should be closed/open circuit to each other?  What's the best way to proceed?

I live in Devon, so not exactly the middle of the UK.

If I can't fix this then I was hoping to get a 2nd hand Coiltek 10" coil and use this Nox as a back up machine for fine work and have a manticore for my main machine.

Cheers

Clive H.

 

 

 

[PimentoUK]

 

"Maybe we can get some insight into the design of the coil and control unit"

It's pretty well understood, I was just sparing you the details. People have been poking around these machines since they came out.

 "I have some electrical skills including a multimeter.  If you could give me some suggestions on how to test this .."

No need for wire-cutting, it's just resistance measurements on the connector pins. Give me a day to sort out the info, I'l post it up.

 

[PimentoUK]

So, here's the pinout of the coil connector:

Pin 3 is the 0V ground.

Pins 4,5 are the two complementary outputs.

Pin 7 is the +3.3 V supply.

Resistance between pin 3 and pin 4 is 2000 Ohms +/- 200 Ohms

Resistance between pin 3 and pin 5 is the same.

Resistance between pin 3 and pin 7 is 3600 Ohms.

I suspect you'll find one of pin 4 or 5 is open circuit.

Q: Does you multimeter have a capacitance measuring feature? Often there's a small 2-pin socket on the front panel?

[CliveHamy]

Hi PimentoUK

Many Thanks. The fault is between pin 3 & 4, it reads open circuit, 3&5 read 1970 ohms, 3&7 read 3560 ohms.

My meter is fairly basic, Resistance, voltage and current. But there is one setting I've never used which has the "diode symbol (+Triangle-) check" gives an Ohm reading, I guess to check if a diode is functioning, will that be of any use regarding whatever you had in mind with the "capacitance measuring feature"?

Ok so we know that there is a break in that 4 wire somewhere in the cable, the gland, or in the body of the coil itself. What's your experience of opening up and replacing the gland on the coil? 

Cheers Clive 

[CliveHamy]

I need to work out where the wire break is. I may be able to borrow a multi-meter with a capacitance function. I guess I connect across the 3 & 4 pin and read off what pf value I get and work out how far down the wire the break is.

 

PimentoUK do you know what the pf value per metre or foot for this sort of wire? 

 

Cheers Clive