My love/hate relationship with the F 75 continues.

I took the F 75 to the Midway area of a fairgrounds today.I ground balanced,reground balanced,turned the sensitivity down to 40,even disc'd out up to 21,notched 36 in order to get it to run close to stable,No dice.I checked the coil connection,everything I could think of.The detector was falsing and very chattery.Dragged out the 2500,bang silver dime,bang another silver dime,bang a 1936 quarter.Lots of clad dimes and quarters.No problem.Maybe I need to call Fisher and maybe send it back to see if it's running on all cylinders.Signed Pensive in Montana

You should NOT have to do this....... BUT......... pull the batteries,,,,,,, then reinstall....... and check again. Sometimes this cures the problems. I hunted yesterday at a few different sites,,, and encountered this problem. The first site..... removing the batteries trick worked. At the second site..... this trick failed. Sooooo, I grabbed another F-75. SAME PROBLEM! This positively verifies EMI problem.

Try a new set of bat

LowBoy

TAKE A LITTLE TIME KICKBACK AND WATCH SOME OF MY DETECTING VIDEO'S BELOW ON YouTube

[www.youtube.com]

If you don’t dig it, then how are you going to know what you’re missing!
How can you have your pudding if you don’t eat your meat!

If you have a F70 or F75 that is operating as it should you have a good unit..
Unfortunately this is not the case with many so send back to Fisher for a check up( seems like a lot of faulty coils) and lets hope it comes back operating as it should..

tom!
does this behavior POSSIBLY indicate a shielding issue of some kind?..or does it generally mean the 75 is exposed to STRONGER emi at the second site,and the circuitry cannot compensate for it?

(h.h!
j.t.

TOO strong of EMI at the 2nd site. Most being induced into the coil.

thanks tom!!
i believe you covered this before,however i am NOT sure,so i will ask again!
if the (e.m.i.) is being induced into the coil at a particular site,AND the site IS unhuntable REGARDLESS of settings,then will mounting the 6" coil to the detector make a difference AT ALL at THAT particular site?..my thinking is taking me to the fact that the (e.m.i.) is COIL induced,as you stated,and at that point in the hunt,maybe JUST the 11" coil is suspect ONLY,possibly because it is a (d.d) design,and the little concentric MAY not be effected as much,or not at all?..bad deduction?

(h.h!
j.t.



Edited 2 time(s). Last edit at 09/20/2008 11:56PM by jmaryt.

I just answered this exact question in a P.M. Let's see if a cut-n-paste works:

Wished it were that easy-a-fix. Problem is,,,,, the F-75 is in extreme overdrive....... so as to achieve the same standard depths as most detectors on the market achieve. And the reason the F-75 is in extreme overdrive is.... the extremely tight (condensed) electromagnetic footprint of that elliptical DD coil ...reduces depth capabilities severely....... soooooo.... in order to reacquire standard depths again,,,,,, the Sensitivity is heavily boosted. The resultant??; ANY EMI within that narrow corridor coil footprint is heavily amplified. This is probably 60% - 70% of it's inherent EMI issues. Painting the top of the coil with shield-paint would only help a few percent. ---- Yes, I was involved with Troy's X-5 coil shield-paint issues. A batch of approx 100 coils were released to market..... with sufficient,,, yet improper procedure shield-paint. X-5 units with these bad coils incurred severe microphonic instability issues. These folks were the Troy folks at the Los Banos, CA Fisher factory. (Unsuspecting) problem was caught fairly quickly.... yet,,,,, some of these coils made it to market. With proper coils, the X-5 is a very good unit. Hmmmmmm...... this stuff should be posted on the forum.

YES, changing to a non-DD coil WILL help SOME..........,,,,,,,,,,,, BUT, may not be the "answer-all". The smaller coil MAY help just enough (in some areas) to allow a specific area to be hunted. My success ratio (thus far) is...... the little non-DD coil reopened about 20% - 30% of these EMI saturated sites. Soooooo,....... I can give you a partial = "MAYBE".

Tom

tom
i am happy to know the the 6" coil will possibly "bail" me out in some difficult sites!..thanks for the very informative post!

(h.h!)
j.t.