I have noticed a 15-100 ADU gradient, brighter at the bottom of the frame than the top, on my QHY8. This gradient is observed on bias, dark, and light frames. It seems to get worse at higher ambient temperatures. Looking at old data I took a year ago (June 2008) the gradient was not apparent but it seems to be getting worse as time goes on. Last winter it was only 15-20 counts but now it has been about 60-80 counts. Letting the camera TEC operate for longer before shooting seems to help some.
Dark or bias subtraction does not always take care of this problem since it changes as the camera operates. I use a 12V car battery for the field and a 12 AC power supply for home. I have used different drivers but nothing seems to make a difference.
Is something going wrong with my camera?
Thank you for any help that you can give.