[mythtvnz] Help troubleshooting signal interference

[Matt Poff]

Over the last couple of weeks my MythBox has developed some weird  
signal interference which obliterates the picture feed to the TV.  
There have been no electrical wiring changes in the house or new  
appliances plugged in so it's a mystery. I unplugged every other  
device from the mains running off the same dual socket except the TV  
and Myth box and unplugged everything else (audio jack, DVB-S feeds  
etc.) from the box but the interference persists even when the Myth  
box is not running.  I even grabbed an extension cord and fed the TV  
and Myth Box of completely different loops with no effect. Only when I  
actually turn off the power switch at the back does the interference  
stop.

I opened the box up to check whether there were any loose cables etc  
but couldn't find any. The only change I've made recently was adding  
another SATA drive to the rig.

I'm assuming the problem stems from the power supply but not sure how  
to fix it? Do I need to ground the box in some way? It's a purpose- 
built PVR case (Silverstone LC16M) so should be fit-for-purpose.

The actual supply of power is fine and the system runs but the feed  
out to the TV is borked. Turning the RCA jack  (good quality video  
gold-plated) in the Video-In socket sometimes improves the picture  
fleetingly. If the system is unplugged from the mains and left for 10  
minutes or so the signal is usually OK on the next restart for half an  
hour or so before the interference kicks in.

Any ideas how to fix or further troubleshoot this?

Cheers,
Matt