I have FCExpress 4. When i place stereo clip on the Viewer it become mono. What is the problem?

When you load the clip to the viewer, do you see tabs for two Mono Channels of Audio?

Then your video is Dual Mono, not stereo.

To fix, pan the audio from Channel 1 all the way to the left:

and Channel 2 all the way to the right:

Now they should play on the appropriate channels.

Once you do this, the audio settings should be remembered every time you load the clip to the viewer.

MtD

Then the source clip is mono.

What originated the clip? A camera?

How are you ingesting the clip into FCE?

MtD

What is F.V.?

MtD

If you open the Log and Capture window, and click on the Clip Settings tab, there is a button that will toggle capture from Dual Mono to Stereo. Check that is set correctly.

Also, try trashing your FCE preferences -

download Preference Manager from Digital Rebellion (free);

http://www.digitalrebellion.com/prefman/

your preference will be reset to factory settings the next time you launch FCE.

Trashing preferences is the usual first step when Final Cut starts behaving unexpectedly.

http://support.apple.com/kb/TS2611

Now try another capture from tape and see if that works correctly.

MtD