Thank you, adam and Grubstake. Let me give you guys a little background to see if that helps. I bought the Minelab 3500 about a month ago, and I read the manual several times through before I used the detector. Right after I got the package in the mail, I checked the detector out. I made sure I could get a target signal with a gold ring, and I checked a few of the features. Everything worked fine then, right at the end of October. It has been working fine with the stock coil, until just recently. I've been slowly using the detector, checking out its features and preparing to use it in some local areas. Last weekend, I took the detector out to a test hole I've dug and I checked out every feature. By the end of the weekend, I'd verified that all of the features work, including the automatic tune function, ground balance and discrimination. Generally I've been running the detector in the fixed mode, but last weekend I messed around with the discrimination feature to make sure it was working, which it was. I have been treating the detector with kid gloves, and I've followed all the protocol in the manual. I haven't plugged the stock coil in while the power was on, I haven't unplugged the coil while the power was on, and I've never turned the detector on without a coil attached to the electronics. I haven't dropped, hit or otherwise adversely treated the coil or the detector. I haven't gotten it wet at all. Anyway, over the last few days I haven't had time to experiment with the detector, so last night I took it out to my test hole and tried to get a signal off a gold ring. I was surprised when I found I couldn't get a target signal at all. I've used the same gold ring for this purpose a hundred times, so I expected a strong signal. I checked all the settings but I could not get anything from the ring or any other metal object, no matter what mode I put the detector in. At this point, the detector was set up to be completely stock, just as I'd been using it from the moment I got it in the mail. At first I thought it was the battery, and I just bought a new stock battery as a backup, so, after fully charging my new battery, I changed to the new battery and checked again. I still couldn't get a target signal with the stock coil. I remembered reading in the manual, under the section on troubleshooting, that if you could hear threshold but no target signal, you should test a different coil. I have an 18-inch DD, which I hooked up to the detector. I got a signal right away. It seems to be working fine. I tested the 18-inch coil with the detector settings suggested in the Quick Start Instructions in the manual on page 12. What I'm wondering is, did a certain feature I tested last weekend cause a short, or otherwise adversely affect the stock coil? I am able to get threshold with the stock coil, but it will not respond to nearly any metal or produce a target signal. I can tune it, and it will verify that the auto tune function has finished running. I did get it to sound off for a second on my aluminum scuba tanks last night, but after a few passes it stopped registering a target signal. It didn't sound like it was discriminating out the signal, and discrimination was set to all metal. It just stopped reading the metal completely, like it wasn't even creating an electromagnetic field. I checked again tonight and it won't read the aluminum tanks or any other metal object. Has anyone else experienced this? It must be somewhat common, if the only suggested fix in the user's manual for a detector that produces a threshold tone but no target signal is to check a different coil. I'll be calling Minelab in the morning, but I thought I'd ask here to see if anyone has heard of this. I would appreciate anyone's thoughts. Thanks for your help.