Firewire problem

[Robert Schoenburg]

In preferences in iMovie you can choose to Play Video Through to Camera.
This is good if you want to see what the project looks like on a TV. To do
this, I connected a Canopus ADVC-100 converter to the iMac using firewire
port, and then connect a TV to the converter. I also have a Western Digital
200GB firewire drive.

Here is the problem. If the project is on the main iMac drive, it works
fine. If the project is on the Western  Digital drive, the video on the TV
is very erratic, and there is no sound. In both cases, the playback is fine
on the iMac.