Gday Andrew,
Well I could try and explain, but it'd be a bit it pointless ... :-) so I'll just cut to the chase instead ...
I just downloaded and ran that Prolific chip checker but it could not connect.
BUT THEN I noticed the WARNING in red on that Prolific site:
Warning Notice:
Please be warned that counterfeit (fake) PL-2303HX (Chip Rev A) USB to Serial Controller ICs using Prolific's trademark logo, brandname, and device drivers, were being sold in the China market. Counterfeit IC products show exactly the same outside chip markings but generally are of poor quality and causes Windows driver compatibility issues (Yellow Mark Error Code 10 in Device Manager). We issue this warning to all our customers and consumers to avoid confusion and false purchase.
As shown in attached I'm seeing Code 10 in the Device Manager!
It seems my friends at MSY have sold me a cheap cable alright.
So I've just ordered this one:
here at eBay
Only two dud cables so far ...
many thanks for your help again Andrew ...
cheers