Mini pulse rev D voltage fluctuation

[bobsuruncle]

Hello all , greetings from Australia. Upon completing the mini pulse kit I have a very insensitive circuit. As in little or no detection on an 8 inch chunk of 2 inch steel axle ! So I went over the voltage checks again only to find that the voltage to pin 4 is slowly fluctuating through 1.5 - 2v to zero and back again . As the voltage passes 500mv either on its way up or down the detector sounds a quick beep and then leaves the zone only to return again in a minute or so . ( I only have a single channel scope and it behaves a little erratically ) So I'm reduced to using a multimeter .Any ideas on what is happening would be welcomed. Thanks.....Dave.

[bobsuruncle]

thanks everyone for the help but it was a crappy pot that was the problem ......oh and thanks again everybody , for your understanding and advice.