I know this is very old thread. But I just wanted to say that I had a similar problem. DSP5200s would just stop working for no apparent reason. What was tricky about this problem is that there were two causes. Of course, the obvious one was a loose connection. The other was loss of communication with the processor. Switching the AC power to the processor off/on did the trick.

DSP6000, DSP5200, DSP5500VC, P300W, SW1600, G68, 568.2, HD621, G57, G55, Oppo BDP-105.