Serial port TS219P

Hoping I can get some help with connecting to and ultimately unbricking my TS219P.

Please see http://forum.qnap.com/viewtopic.php?f=147&t=95908

or:

I cannot power on my NAS with the serial adaptor connected to my laptop.

TS219P
http://www.amazon.co.uk/PL2303HX-RS232-Cable-module-Converter/dp/B00AU00BWC
https://www.adafruit.com/datasheets/PL2303HX.pdf
Windows7 laptop

Following here http://www.cyrius.com/debian/kirkwood/qnap/ts-219/serial I see pins 1 and 4 labelled on the motherboard and connected my adaptor accordingly.

With the adaptor connected I can't power on the NAS.

When I pull the adaptor from my PC the NAS powers on.

Took apart the USB plug. I see the following:

1. 5U connected to red
2. RXD connected to white
3. TXD connected to green
4. 3.3U not connected
5. GND connected to black

Can anyone confirm I am mapping the above to the colour codes in http://www.cyrius.com/debian/kirkwood/qnap/ts-219/serial/ correctly?

Red USB to VCC pin 2 (green per the guide)
White USB to TX pin 1 (red per the guide)
Green USB to RX pin 3 (black per the guide)
Black USB to GND pin 4 (white per the guide)

With the above connections, when I plug the USB into my laptop, the NAS lights come on (power blinks red and green) and the fan twitches - with or without the PSU to the NAS being connected. But the NAS will not power up.

I'm non-technical but OK at following instructions.... I wonder if my adaptor has the wrong voltage? I understood from the datasheet that it auto regulates to 3.3V but perhaps I'm reading it wrong?

Final bit of detail: I found that the NAS will power up with the USB connected to my laptop if I disconnect the Red USB to VCC pin 2 (green per the guide).

However I don't see anything on my terminal emulator.

thanks in advance

Paul