Tech@ZWO Did you test the camera with different cables in ASIStudio to rule ou the problem with the camera?
Why do you keep asking customers to try matching different cables to your cameras? If a cable works with other devices, it should also work with your cameras.
The fact that a particular cable does not work with a particular camera can simply be caused by the camera's USB hardware/firmware or the ASIAIR USB hardware/firmware are not designed with proper engineering margins.
You need to have a known set of test cables with different lengths and test a camera during QA with a number of ASIAIR (which also has less engineering margin than a well designed computer USB interface -- that is why some cameras will connect to a computer, but not to an ASIAIR). If any combination of ASIAIR/cable does not work, do not ship the camera to a customer to make it become their problem.
You need to also do this when QA'ing an ASIAIR before shipping the ASIAIR. Test the ASIAIR against a range of cables and cameras.
When a device is returned because it has problems, you can then check it against the known process. The key to good engineering is a set of good process to follow, and tune the QA process to improve the quality of the shipped product.
There are two ways to ensure that the customer does not end up with a defective unit -- one is to make sure the product is designed with sufficient margins in the first place. The second is to perform QA to weed out the units that don't meet the proper margins, so they don't get shipped. 4 ASIAIR and 4 different cables will take 16 tests to pass QA for a camera, for example, and likewise, 4 cameras and 4 cables will take 16 tests to QA an ASIAIR. And if there is still more than 0.01% failure rate, increase the number of tests.
This way, your paying customers do not end up being a replacement for your QA department, and having to perform the tests themselves.
Chen