Hi all,
Thought I'd close out this thread with an update of how things have progressed and been resolved.
I lodged a ticket with QHY support who instructed me to do some troubleshooting, mostly checking voltages and waveforms on the main board in the camera using an oscilloscope. The DC-201 is ok, but I wasn't getting the right signals on the main board. My electronics friend spotted a broken track running from one of the ICs to a connector, so he jerry-rigged a new connection using thin copper wire. Much to our delight this mostly resolved the problem to a point where I was able to take images, but I still wasn't convinced it was fixed properly. The exposures still weren't quite right and daytime targets were a bit flared from memory. There was some noticeable corrosion in a few spots on the board which may have lead to the broken connection.
I requested a replacement board from QHY which arrived within a week for the sum of ~$180AUD. I finally replaced it yesterday and whilst I haven't tested it at night, daytime tests and exposures appear to be much better and the camera appears to behaving as it should. I sprayed the new board with a protective lacquer to hopefully prevent any new corrosion.
Hopefully I can put it through its paces soon
Cheers