The dark side of manual shutters

[cunim]

I know you think this isnt a power issue, but could you describe your setup?

Dell Studio XPS16 (i7, w7/64) with 1394a port disabled.
Sonnet Firewire 800 Pro expresscard adapter
Sonnet wall wart or Tekkeon regulalted battery to adapter.  Tried various volatages but adapter seems most stable at 12V.
Three different 1394b cables to the back, including one from Hasselblad.