F75 coil testimg

Is there an accurate method of testing the 11" coil other than switching out for one known to be good? I am experiencing continuos high tone falsing ( truncated high pitched peeps ) regardless of sens/disc settings which correspond to TIDs in the 90s at the rate of 3 or 4 per swing. It also appears to occur whenever the coil makes even sliight edge contact with an objject but not so much if contact is on the bottom. All connections appear tight.

I believe I have seen a thread here about this but my searches have proven fruitless.

How old is the coil?
If you lightly tap the coil wire with your finger..... what does the unit do?
Try a totally different Grnd Bal number. If you are on '90'.......... then try 70, 60, 50, etc..........regardless of balancing to dirt......... and see if you notice any change in error.
Is the unit more 'reactive' to damp/wet grass?

I appreciate the response. The coil is new ---came with the machne about a month ago. I don't remember so much high number falsing the first half dozen times I used it but the interference on Sunday was so bad I gave up and turned it off. I didn't have much opportunity to hunt this evening so I had to settle for a quick hunt at a nearby school I frequent a good deal with my e-trac. I have a small test garden there with some clad coins at 8". I searched a good clean area before I used the 75 and reset to factory before I started. GBed at 83 and was probably the stablest I have had the machine up to about sens 75. I could not duplicate the falsing by tapping the coil either with my finger , a1/4" dowel or touching a tree trunk but it continued the falsing while sweeping even with lowered sens(40) and still corresponded to high TIDs like 93 and up. I know White's and Minelab machines both have methods of blocking "wrap around signals" , what ever the hell those are, that read at the top of the scale. Is this what I'm experiencing? Damned annoying feeling you have to check high tones to see if they repeat 3 or 4 times a swing. The only coin in my garden which the 75 could hit was a flat quarter @ 15/60 dp 4h. Hit them all with threshold zips in all metal

Unfortunately the dinner bell rang before I could try changing the GB number so I'll have to try that tomorrow. BTW--this ground is school yard which is well watered while the Monday area was a city park which hasn't had appreciable moisture since probably Thanksgiving---very dry--we're an 8" a year place that's in a drought!

Yes.... try a different Grnd Bal set of numbers.......... and a Disc of '10'.

Tom, I'm about to hit a rainy field, any recommendations if it starts to go off on swings? (Damned rainy Portland oregon!)
Thanks!

Put Sens on 99 and Disc 4. This should make the unit EMI prone. Then........... use F1 - F7 ... and find the best channel to reduce EMI. Then drop Sens to 60...... keeping Disc on 4. See if the unit is reasonably stable. If not..... then jump to Disc 5. If still unstable....... change Grnd Bal numbers in units of '10'........... maybe several times...... 90, 80, 70, 60, 50 ..... etc.......
Increase Disc to 10 as a last resort.

This procedure is slightly different from recommended EMI mitigation steps given in "Rcpt Ack of F75 Proto" thread.

Tom Thanx again for the time.
Tried three different venues today . The last was the school yard I hit yesterday. GBed @ 84 same settings as yesterday. Everything ran about the same perhaps alittle more EMI but I was frustrated after the earlier two sites at that point. Changing GB number provided no joy. Little difference either way. At 54 there seemed to be a little less high tone falsing but in a stretch about 5'x10' I seemed to encouter 25 to 30 high tone falses regardless of the ground balance with the same sensitivity setting around 70 and it doesn't diminish until the sens drops down in the 40's. I experienced the same behavior in a sububan orchard which GBed low 70's --Rio Grande caliche soil lot's of buried trash. In between I hit a city park where EMI "static" sounded like a machine gun even while attempting to ground balance. While there I even tried to turn the disc up to 65 as if I was only going to seach for quarters & dimes which created what sounded almost like a threshold of static as if all the discriminated targets were bleeding through. I do run the the machine at full volume and control the sound with my headphones as I always have with all my detectors. If this is a no-no ,I missed that part in the manual. I have noticed with the 75 that I have to run the headphones nearly at full volume while on my other detectors I run them significantly lower. I'm guessing that may be related to the great battery time but that's another matter. Frequency shifting at the middle park where interference was so bad was futile.

I've gotten my friend to go along with letting me hunt behind him and his MXT tomorrow for a couple hours at what appears to be such low operating settings to see the results. 75's last chance before it goes back to the factory I'm afraid.

It is indeed sounding like something is in error. Too bad you do not know someone (or a local metal detecting club) that has a F70 or F75..... and can borrow their coil ....... for troubleshooting/further problem isolation. The 'volume' control on the F75 has nothing to do with EMI problems.

Now.......... if you are hunting areas that are carpets of nails........ or a lot of flecks/flakes of rust/iron decay..... this will cause exactly the problem encountered; however, you have been to 3 different sites...... with no appreciable delta/differential.

If you sweep the coil say 15" above the ground......... do you hear the same EMI/interference? Or does the problem linearly become more apparent as the coil is being swept....... whilst lowering the coil to the ground. In other words.... Is it the ground that is causing the falsing issue?

3 venues THAT day but , the same issue @ just about all the locations I've visited. i didn't think the volume was involved but was grasping. Leaving shortly to do a head to head with my friends MXT and will keep the 75 @ settings which make it stable regardless of the magnitude of the settings to see what occurs. Will try swinging above the ground as you suggest--my guess is it is the ground as the machine is usually pretty quiret without motion at moderate settings. When motion begins the static occurs which seems to be counter to much of what I've read. I have a meeting Monday with some detectorists (about 25) but to my knowledge none of them run Fisher. Thx again

I managed to get out for a couple quick hunts but unfortunately Tom I don’t think any conclusive evidence appeared. The first was at what’s probably the oldest park in the Duke City. It’s always had a ‘bad” reputation but has lots of day use and clad recharging activity if nothing else and was my buddy’s choice with his MXT. Very hard , dry , compressed straw brown grass thatch very high trash GBed @91. Factory reset and then notched in a semblance of high trash coin disc. setting –nickels copper dimes and quarters only. Stability ended if I exceeded 32 sens. and mostly ran around 27 or 28. The machine works and located the same surface coins as the MXT but we found nothing of depth to compare. I did manage to confirm to myself as well as my friend that the pinpoint depth indication on the 75 is way off. While it consistently showed depths of 3 or 4 inches when hard to the ground they were never beyond the reach of my pro-pointer. I have confirmed that today with my hunt as well as shop testing that there is a consistent 2” to 3” error in pinpoint depths. A 5” plug seeking a coin at that depth always has a coin somewhere in the middle.

Today’s hunt was much the same but I tried swinging above the ground as you suggested. The only discernable change was in the volume of the high toned falsing not the frequency. It just seemed louder and more distinct while scrubbing the ground. Today was newer park (1980’s) that was getting some water -GBed @83. I used the same disc settings as the day before as I was too lazy to redo them with much the same results. I tried to push stability and in a few areas managed to run quiet to 45 sens. but no more. Deepest readings were 5 or 6 inch targets that were never more that 3. After 90 minutes I switched to my e-trac and consistently dug clad in the same area at honest 5 and 6 inch depths before the driving sleet chased me away.

This evening in my garage at stable reset settings of 15 and 65 WITHOUT MOTION I confirmed the inaccuracy of the pinpoint depths by moving the targets over the coils---both show the same error.. I also found that any coin in contact with the coil creates an overload response whether it is the 11 or 5. Does any of this sound normal?

With or without a coil installed to the control box stability is lost with disc below 5 when sens. exceeds 35 or 40. I could deal with constant click , pop and low tone static as it almost has a threshold effect as to the number of targets that may be getting discriminated out but the 3 or 4 high tone falses each swing that require repeated checks for repeatablity seems as if it would be unacceptable and unenjoyable to most anyone running a detector. Makes for definite 2 steps forward one and a half step back experiences.

Your frustration must be high..... and your patience must be running out.... by now.
I'm not so concerned about the depth error. And the overload signal with a coin very near the coil is 'correct'. No errors.
What concerns me is..... you are still acquiring EMI without a coil. THAT'S a problem. That's a 'return to factory' issue.
And........... if you are receiving EMI conditions with the 5" coil installed.......... especially with factory presets.......... that's also a serious stability problem.
CALL FTP (you will probably talk to Felix)............ and............ if the unit is under warranty in your name........... Felix should send/e-mail you a UPS shipping label. Send a note with words like: Severe instability/EMI even with low Sens settings and low Disc settings. EMI encountered without coil connected..... at factory presets.

Not quite a perfect world!

Thanks for your input Tom. I've held off making a call to El Paso yet as I'm going to a remote location this weekend where no EMI issues should occur although there's no telling what's flying aroud in the White Sands area. I want to see how it acts there first but I will be talking to them about the pinpoint depth issue which is a real inconvenience if you're coin hunting--especially in someones new mown lawn.