What's wrong with my HH?

[WesP]

I haven't had any luck getting my HH to work. The scope says most of the test points are putting out the proper signal but TP4 is a mess. See the attached pics of the scope at the diffrent TP's. Ignore the slope of the signals on the second channel. My scope is an eBay special and for some reason the second channel shows a slope on all it's output.

[KingJL]

Were the tests with or without the coil connected? If they were with coil connected, test again without coil. If the oscillations are not present with coil disconnected, check your damping resistor and coil connections.

If oscillations persist without coil connected, I would recheck all parts in the pre-amp section.

This may sound like a stupid question, but:
What part are you using for the pre-amp? Are you using the as designed parts? It appears that your pre-amp circuit is oscillating. I used a AD797 as a 1st stage pre-amp with low (10x) gain. It would oscillate until I shunted the feedback resistor with about 10pf. But that is not the problem if you are using as designed parts.

[WesP]

My Ringing Problem = HUA

Were the tests with or without the coil connected? If they were with coil connected, test again without coil. If the oscillations are not present with coil disconnected, check your damping resistor and coil connections.

If oscillations persist without coil connected, I would recheck all parts in the pre-amp section.

This may sound like a stupid question, but:
What part are you using for the pre-amp? Are you using the as designed parts? It appears that your pre-amp circuit is oscillating. I used a AD797 as a 1st stage pre-amp with low (10x) gain. It would oscillate until I shunted the feedback resistor with about 10pf. But that is not the problem if you are using as designed parts.

All tests were done with the coil connected. It stopped ringing without the coil. After looking again at the hookup of the coil I realized I had it connected to L1 and L2! When properly connected it doesn't ring. And I get a healthy fly back peak.( See Attached scope shot.)

All components are per parts list. IC6 is a NE5534.
Now my problem is I get no detection at all. The speaker is putting out a constant clicking which will vary when the auto track switch is turned on-off and the threshold pot is varied.
It doesn't change at all is metal is moved close to the coil.
any suggestions on where to look for the problem

[amtech2005]

What's wrong with my HH?

WesP , Try with just 1 search coil not 2 ? Then re-test at TP4 with o-scope before the 4066 switch. Sounds like your very close to solving problem anyway !! Eugene

[KingJL]

Progress???

Wesp,
Any progress or any additional sysmtoms with your HH?