The old one was returned because the USB port stopped accepting charge and the GPS stopped working. I actually suspected the two problems were related. Unfortunately the GPS is still not working - in fact using a system monitor app it appears there is no GPS sensor present. I can only speculate that either the sensor is faulty or disabled (maybe there is no GPS driver installed?)
You could try doing a full wipe perhaps.... That would be my first idea. It probably doesn't have SDE installed so you can't do full format. I think SDE kills warranty.
But these tablets have always had flaky GPS. There are a number of hardware revisions of them, which Archos uses as an excuse for their inability to deliver a reliable OS, and there are probably quality control problems too, and perhaps some of hardware is simply cheap unreliable junk.