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Thanks to Gradius and everyone that contributed to this post; I now have my 500gb drive back. The £2 cable I got from Ebay worked perfectly, although I did have the RX and TX the wrong way round. *I didn't need to connect the GND to the drive. I used the paper trick, 1 for the motor and another for the connector, bit of overkill. If you're unsure about cables, use the ebay guy. Saves you having to buy twice!!!
If anyone is looking for a cheap CA-42 cable, try seller 'ukmobile786' on ebay. He has the CA-42 for £1.99 including UK postage and he is very quick in sending it out. I'm awaiting a T6 driver to remove the screws on my drive, so will update you later on whether I've been successful in de-bricking my STM3500320AS. The CA-42 cable I received has 3 wires only, GND, TX and RX. I've tested the cable in hyperterminal and everything looks good to go. (My cable pinout*: Red = TX, Blue = RX, Orange = GND) *Make sure you find your own cable pinout to minimise the risk of shorting anything.