I have had this problem on my 500s, I have found away how to clear it, but it isn’t for the faint hearted, but honestly it does work..
I had problems with the tuner losing signals and the green motor light would go out, I found by putting a bigger psu on it 1 amp seemed to fix most of the problems most of the time however I have had the same problem as you have loss of signal etc, I found it by accident and it does work, basically I had another psu unit but its output is 19v, I accidentally plugged it in to the d500http://www.satellites.co.uk/php-bin/forum/images/smilies/smilies/bash.gif
:-bash and as I was setting up the motor the box did a reset, I then realized that I had used the wrong psu, (to many wires to mention), I was pooing my pants when I reconnected the other psu 12v 1 amp and to my great relief it rebooted and worked as normal, I had to do this on a few occasions when the 500s was using the motor, it worked well for me, the box is still running fine but I use it just on my fixed sky dish and haven’t had any lockups at all since its been on this dish..
If you do try it ensure the polarity is correct
Simon