(Forward: This blog article began as what I felt would be a straight-forward documentation of an obscure sector of the old Packard Bell computing world. It cycled into a lot more and became a massively rambling mess spanning months of time, especially the latter half involving the master CD chaos. I used this blog in part for real-time notetaking while I worked on the system.)
TL;DR: You really don't need to use the PBTV5 tuner card to still get composite video input on the Platinum TV-capture capable machines from 1996-1998. Using the card for coaxial input requires a custom cable and it can be easy to short the wrong pins out if you aren't careful. With the loss of analog broadcasting it is rare to need that coaxial input at all, proceed at your own risk. Also Packard Bell master CDs, not a fan of them.