Can you try looking for the signal on the PC, using Hyperterm w/ an RS-232 adapter?
The config should be 9600,8,N,1 ( IRRC )
the signal is just plain text
e.g.

14.7
14.7
14.7
... etc,

BTW. as data goes, the 0-5v is massively superior to the slow, coarse, serial data. It is 500 samples/second, vs. 10 samples/second for the serial. And, it has active ground offset compensation.