What does a TBC do?

[Tripitaka]

To be honest the Wiki entry for TBC's is very good:

http://en.wikipedia.org/wiki/Time_base_correction

If your after a master sync I highly recommend this one (having used one in a professional studio for several years):

http://www.amiga-hardware.com/showhardware.cgi?HARDID=1298

Of course, many studio quality video units have built in TBC's but they are often completely rubbish or at least a bit iffy.

IMHO most video errors are caused by one of three things, improper sync, improper termination of the video signal (easily spotted as your video signal will be over bright), or a lack of understanding of the video standards themselves (particularly aspect ratios and drop frames).