It was the PC.

I loaded the program on an old PII 233mhz, W95 system, and it came up
working immediately.

For those of you who encounter a problem like mine, and who might
benefit from some voltage/current data, here is what I measured for
my future reference:

My TS-850 measures +7.4vdc with the key open.
when keyed, the circuit draws 1.5ma from the ts-850.

My cw interface requires 4.5vdc to drive the
2n2222 into enough condution to key the ts-850;
at that point, the interface circuit draws
0.8ma from the keying source. I performed these
tests using a variable DC supply for keying
the cw interface.

I put a scope on the interface input from the PC, and observed
-10vdc unkeyed and +10vdc when keyed by the program on the
old PC.

Huel
k4drq