We have an older model Yamto Lock Metal chek 9 metal detector that has been giving us some troubles. It will not always pick up the test pieces. they are 2.0non fe, 2.0 Fe and 2.5 SS, we have turned up the sensitivity. This units is a drop unit. We run dry product through it. IS There anyone close to us that could look at it for us. everyone tells us that there is no parts to fix these. Was said to be one of the best units when they first came out. Need some help. thank you