During my earlier attempts at modifying the Explorer something happened, due to my actions, caused a very similar problem to the one you speak of.
1. The power supply in my Explorer had some how become defective, most likely due to the fact that I once managed ACCIDENTLY reverse the battery poles and attempted to turn the unit on . This did away with all my saved programs, but believe it or not, the detector still worked fine for quite a long while.
The next time this problem occured,It would mostly happen after about ten minutes of using the detector.
It could have been a consequnce of:
a) dropping the control box(that I had seperated)and the impact my have damaged the solder joints of the larger components that make up the power supply:
b) The moisture that had got into the electronics, which I duely sprayed with a water/moisture diplacement spray(electronics friendly)the moisture may or may not have contributed to the problem.
or
c) The initial reversing of the polarity had finally caught up with me.
I returned the control box back to Minelab and there techo's fixed up the power supply(quickly) and charged me about US$70.00. That was about a year ago and I have used this modified (Land And Water)Explorer quite a lot.
It may be your power supply.
It could also be due to the internal PCB's not connecting or have disconnected form there multi pin connection points and there is a bad connection at these points. IT IS UNLIKELY BUT NONE THE LESS POSSIBLE.
If this problem persists with your Explorer then I suggest you return the detector to Minelab.
Hope it is still under warranty?
If not, then there is really no alternative unless you understand electronics enough to help you repair the Explorers' power supply or whatever may be the cause. I would take the option to let Minelab do any repairs. Just remember that the Explorer, like many other devices, is a MANMADE product. Things of this nature can and will sometimes most probably go wrong. It's knowing that even if they do then there is a repair alternative that will help to put you back on track fairly quick, which will always depend on where you are located in relation to a Minelab repair centre.
I hope this helps you.
Hardnose