34s flashing cable possible candidate?

[jebem]

If it was mine, I would cut the plug, take a multimeter (or even better, a oscilloscope) and do some checks. The serial interface works at TTL level, and the signals should swing betwwen 0Volt and 3.3Volt.

But before doing so, I would plug the USB side to a PC and see if it is recognized as a serial COMxx port, otherwise it is no good for what we need.