While the metal detector is off, hold down the power button for approximately 5 seconds until you hear two, fast beeps.
Sometimes a metal detector will act erratic for no apparent reason. The first step in troubleshooting any metal detector is to return it to the factory settings to see if this helps.
Here is what Garret suggest to troubleshoot an erratic AT Max metal detector:
If a factory reset doesn't do the trick for your metal detector, it is a good idea to make sure the coil is in good condition, the coil plugin is snug, and the coil wire is not dangling over the coil causing it to go off. Then, take off your coil cover and make sure it is free of dirt and debris. Sometimes small pieces of iron can find their way into a coil cover. If that is not the problem try another coil. If you have another coil lying around or know someone who does, it is not a bad idea to try another coil to see if that is the problem.
Change The Frequency
Additionally, the Garrett AT Max is a very sensitive metal detector. This is good for detecting but can be a hinderance in certain circumstances or locations where there may be a lot of external electromagnetic interference or other metal detectors (cell or radio towers, electric lines, etc.)
To change the frequency on the Garrett AT Max simply press the FREQ button to scroll through the frequency settings. Choose from four minor frequency adjustments (F1 to F4) in order to minimize interference caused by electrical sources or other metal detectors. Note that initial button press shows current setting.
Many new detectorists think cranking up the sensitivity is a way to get the deeper, smaller targets. While this does help a little, it can be a hinderance in many cases. Try reducing the sensitivity of the detector. You may be able to tune out some of the interference and you won't really lose that much depth by notching it down a little.
As mentioned above, your location may be the problem. If you are inside, that is likely the problem. If you are outside experiencing this issue, try a different location a ways away from your current location. If this doesn't solve the problem the next step would be to contact Garrett to start a ticket to have them take a look at it.
Luckily, if you have a Garrett metal detector, you have bought a machine that is covered by one of the best warranties, service, and support in the industry.
You can visit their website by clicking on the logo below to find out more about Garrett Metal Detector warranty support.