Hi,
This is my experience sending a QHY12 back to China for out of warranty repair.
First off with QHY you must go through their ticketing system, on their website you go to the section of raising a ticket for repair, they will then email back to you a shipping address for their repair centre, and a form to fill out, ticket number, return address, fault description etc.
I then used Australia Post to send the camera back, air freight (no insurance) and cost in 2017 $ Aust 65.00. A week or so later I got an email for the repair bill and it was $70 for a new main board and I paid an extra $20 to have the sensor cleaned and finally $65 for return air freight . 5 weeks later Aust Post delivered it back to my door.
So please don't send the your camera back to ZWO without a Return Authority Number (or ticket number) otherwise it will sit on an in-bench somewhere in China with no paper work.