Bad Coil???

[rob.ream258]

Is there a way to determine if I have a bad coil? Reason being, I took my F75 to the beach for some dry/damp sand searching and started getting very jumpy signals from that point onward. Given the salt water, I wasn't too concerned and excepted the noise. I turned down the sensitivity which dropped the noise some and kept on swinging. The following day I went "turfing" and the noise was still there. I started the normal troubleshooting and found that with the coil 5 feet in the air I still had the chatter in my ears. Wasn't EMI so........something just aint right.....

Did the salt water get into the coil? Is there anyway to search for hairline cracks other than a visual - i.e. different lighting - squirting some crack finding liquid ???? Did it come from the wire connector??? And no - the electronics didn't get wet - just the coil.....

I can't swap on a new coil or barrow one.......any suggestions? Once I find $150 laying around I'm going to buy a small coil but....

Are the coils under warranty? Should I send the entire unit in for the DST upgrade and ask for a coil test at the same time? That will be the same cost of a small coil and might be a better choice...

Any words of advice?

 

[NE Digger]

First, unscrew your coil connector and screw it back on, making sure its 100% tight. then............do a factory reset and see if the problem doesnt go away. For some reason, sometimes an f75 will just kinda go a little bonkers, and a reset will fix it. Its happened to me a number of times. Its possible you have a bad coil, but they are fairly reliable compared to some others. Does it false easily if you tap it or shake it??

 

[ramer]

Every few months I disconnect the connector from the control box and spray the contacts with contact cleaner. It keeps them clean and removes dirt and moisture. Move the connector back and forth a few times to get the contacts good and clean and spread the cleaner all around and then screw it back in fairly tight.
This may not help in your situation, but over all, it can't hurt. A word of caution, make sure the contact cleaner you use is not harmful to plastic. It will say right on the container if it is safe on plastic.

 

[still looking 52]

In my limited experience I've never heard of any way to check a coil other than replacing it with another coil out here in the field. The two previous posts are good things to try and definitely wouldn't hurt anything. All the internal parts of the coil are sealed from the factory for protection but that also makes it impossible to check or repair in the field.

 

[jas415]

I would do a couple of things: Remove the coil cover if you have one on, do a reset, remove the coil and power it up and see if it is still making noise, and attempt several ground balances and quick grabs in an area you know is pretty clean. Mine has gone crazy on me a couple of times but it was always a matter of resetting and doing several ground balances.

 

[rob.ream258]

Thank you all for replying and sorry to all...........this is operator error. I acquired the 5" sniper for the F75 and had the same jumping with the coil in the air. I started messing with the settings / modes / discrimination levels and found that as soon as the discrimination was above 5 the machine went silent. Not sure why, but both coils are acting the same way. The stock is over a year old and the sniper is brand new and never used as far I know, it definitely looks new.

In the above scenario, I think the caked on salty sand was causing the jumping at the beach since I was running around 25 on the descim and normally run at 0 in the turf. Not sure why my machine has a new personality, but I can live with it as long as I can figure things out. Also, when I was messing with the machine with the new coil and doing some air testing, I found that my wife's gold ear rings were hitting around 15-19 which was a complete shock............especially since I was running with the discrim around 25 at the beach. Bummer.............Also during the air tests I found that the new coil couldn't see anything past 8".......not even a giant $1 coin........wow..........complete shock. I'm going to test this again in real dirt since this machine should be hitting around 12-14 at the least.

Ran the new coil this past weekend and found some clad..........not sure if I like it or not. It's very light and low surface area - definitely got to work on learn a new swing speed.

Any thoughts or help with this small coil???

 

[REVIER]

In the top end Fishers is a bit of programming that is not exactly a boost in sensitivity per se but has the same effect.
Really it switches the unit to a slightly different type of discrimination process above and below these numbers which is more susceptible to EMI.
Supposedly not more depth but just more sensitivity in play.
Remember the disc numbers between 5 and 20, (I believe), as the quietest "sweet spot".
A big difference between 4 and 5 regarding EMI problems at some sites, also over 20.

As an aside manipulating the thresh goes a long way to quitting these things down without losing sensitivity to small targets if you set it right.
Also in my experimentation I have read over and over on these high disc does not appear to affect depth much at all as it seems to on other units and brands.
In my experience it seems to be pretty true.