Too sensitive?

[mykaitch]

My copy of the Tesro UmaxII is very sensitive when the head hits anything like a small tuft of grass for instance.I have had it on the bench with scopes connected and no matter how I hit it nothing appears wrong. As soon as I take it out to test the problem returns. Any ideas???
PS Since I fixed a genuine build error it is much worse. In AUTO it is pretty good, the problem is MANUAL + ALL METAL

Thanks for any advice

PPS using home made concentric that nulls at 3-4mV

[Altra]

Sounds like your coil shielding. Can you make it sound off with your hand touching the coil?

[Koala]

Yep sounds like the coil shield. Usually worse of the grass is damp or wet.

Also does the same thing if the ground balance is too negative. Normally the more negative you are the more depth you have on silver but go too far and every little touch give a false signal.

[mykaitch]

I'll try my DD but the concentric is very well shielded with a lot of EMF spray (RS) and connection too it via copper tape so it should be good - hope so cos its sealed. Thanks for pointers!

[ivconic]

I'll try my DD but the concentric is very well shielded with a lot of EMF spray (RS) and connection too it via copper tape so it should be good - hope so cos its sealed. Thanks for pointers!

Just for experimenting purposes do reverse both; RX and TX pins at coil connector (or even easier at pcb).
Reverse TX pins and reverse RX pins respectively and than see what will happen.