F75 PROBLEM

Hi everyone...Sorry I didn't follow through with my first forum query but I'm having serious problems with my f75.
Six weeks ago I was detecting on a site I'd done several times before when I encountered a problem.The VD went ballistic digits flying around
and generally unstable.I tried lowering the sensitivity really low and the Discrim up to 30 to no avail,I decided it must be to do with condensation due to the weather conditions so I returned home.I kept the machine in a warm room for a couple of days then I did a factory reset and returned to a different field and the machine was fine, everything back to normal running at zero disc and max sens and has remained stable for the past 6 weeks
Yesterday I returned to the field and exactly the same thing happened again. On both occasions it started after roughly half an hour into the field and more or less the same spot not far from Telephone cables but in the past they hadn't caused a problem.
What I did become aware of was the fact that there was a tractor working close by in the next field on both occasions,could this be the cause of the problem.
This time the weather condition's were good so I'm ruling out damp. I tried a factory reset on site but this didn't help so again I returned home.
On returning home I tried a reset but it was still very very unstable, the digits are not erratic but its extremely noisy . If I turn the Disc up to 5 the noise stops but strangely the Sensitivity make little difference....The big problem is when I turn the Disc to 5 and the machine is stable it cant even find my spade ,no signal..
I realize this is very unusual behavior and there will be many factors to take into account....Firstly was it just a coincidence that a looming fault just happened to show up on the same field after the same length of time...Could a tractor cause this kind of problem...If anyone as any idea whats causing the problem could you please let me know...Regards from the UK John

On the tractor issue, some tractors are now equipped with transponders and GPS to regulate fertilization and guide steering, so EMI is a possibility from that I would assume. I have personally not had any issue with it though?

Does it happen in AM as well? Or any of the other modes or processes? Does it happen with the coil off the ground?

Temp extremes can ruin electronics so be careful to keep the temp within limits for both coil and circuit boards.

Do you carry a cell phone with you?

Is the British gov't shooting you with EMI to keep you from "stealing antiquities?" just kidding

jamt225 Wrote:
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> On the tractor issue, some tractors are now
> equipped with transponders and GPS to regulate
> fertilization and guide steering, so EMI is a
> possibility from that I would assume. I have
> personally not had any issue with it though?
>
> Does it happen in AM as well? Or any of the other
> modes or processes? Does it happen with the coil
> off the ground?
>
> Temp extremes can ruin electronics so be careful
> to keep the temp within limits for both coil and
> circuit boards.
>
> Do you carry a cell phone with you?
>
> Is the British gov't shooting you with EMI to keep
> you from "stealing antiquities?" just kidding


Thanks Jamt for your reply....I haven't tried it in AM mode or with the coil off ,I'll do that tomorrow to see if the interference disappears. All the other modes act in the same manner.. I tried lifting the coil in the air and its still noisy .....I know the British government is shooting us a load of s**t but I don't know about the EMI'S...John

Check the tightness of the coil connector on the back of the control-head.

You are not crazy! It was the tractor the drove your machine nuts. I have had the same experience and its so frustrating. I have an old grove I hunt and its way out in the boondocks. There is nothing anywhere near this spot and I was recently out there when a combine started working the field next to me. I thought nothing of it at first because he was in a huge field, 500+ acres. However, when he started getting closer on one pass my F70 went nuts but then he made a turn and went once again to the far side and the machine quieted down. Every time he came down to my area the detector became unworkable but he time he went to the far side I could detect.

Unsupressed plug wires...........and unshielded distributor. Same with motorcycles.

I think it is EMI and I have hunted with guys edging their lawns and my LTD went a bit crazy....We were hunting one area and dogs were barking and I told my friend maybe they are causing EMI after they stopped barking I found a opium pipe. But for sure it sounds like EMI.
We were hunting a Castle and they just put in lights big ones above the ground coming up from the grass the lights were off but our LTD had a hard time detecting...EMI???

LowBoy

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NASA-Tom Wrote:
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> Unsupressed plug wires...........and unshielded
> distributor. Same with motorcycles.

Thanks Tom and everyone for your help....
I tried the F75 again today and I'm pretty sure its nothing I can repair....I did all the tests you suggested. Checked the connection, it was tight...tested without the coil, it was still very noisy , tried it in AM mode its was pretty much the same,so I've posted it off today to the F75 repair guy..the strange thing is you only have to turn the Disc up to 5 and it becomes stable, but it cant find a target at any distance..I just cant understand why it should happen on the same field at more or less the same spot [An area I've detected many times before without any problems} the only difference was when I returned home the first time it was very noisy but it would signal a target ,today it couldn't pick up a target at all on any setting......Do you think its possible for some kind of EMI to damage a machine???? or is it just a coincidence that it happened at the same spot twice with a 6 week gap in between......very strange!!!!

Good luck. Let us know what you find out.

Really sounding like a detector problem.............especially when you can detect nothing,,, with a Disc setting of '5' or higher. That's a major problem.

Thanks everyone...I'll let you know the outcome.....John

I`m pretty well convinced this sounds like outside Electrical interference to me. If it was a electrical fault in the detector it would be doing the problem all the time. The fact you say its only doing it on that same field points to me that there is a large Electrical wave of interference coming off something, be it over head or underground high electricity power.
I seriously doubt its your detector at fault by what you`ve told us.

jamt225 Wrote:
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> Good luck. Let us know what you find out.
Hi Everyone .Just got my F75back from the repairer,apparently it was a coincidence that the problem arose in the same field,it was infact due to a couple of dry joints.I took it out today and found lots of coins ranging from 2 Cartwheel pennies 1790's plus lots of Victorian and Georgian pennies, a nice George 4th siver Halfcrown,3 silver sixpences 1812, 1826,1946. a ring ,a seal and a trade token from 1792... so I can honestly say the F75 is firing on all 6....I'll post some pictures when I found out how to do it on this forum....Regards John

What is a 'dry joint'? Bad solder connection???? And........I presume it's air-test performance is quite a bit better now.

yes!..a "dry joint" is considered a "no solder" ,OR "poorly" soldered connection that "probably" broke,and created a "short"
to ground,OR an "open" circuit,and subsequent "loss" of continuity.

(h.h!)
j.t.

NASA-Tom Wrote:
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> What is a 'dry joint'? Bad solder connection????
> And........I presume it's air-test performance is
> quite a bit better now.

Sorry I didn't realize Dry Joint was a British expression.. You're both right its just a poor soldering job.Whats so frustrating is the fact that when it first showed signs of having a problem it was still under guarantee,I thought it was a condensation problem then after a couple of days it worked fine.6 or 8 weeks later when out of guarantee the same happened again and cost me around $150 to put it right.....Still looking on the bright side,I've got it back and its working fine,my back up machine is a Troy Shadow X3 but I haven't really got used to it yet,it seems to have good depth but I struggle to tell the difference in sounds therefore I'm digging lots of trash....John