Problem with BIAS Frames from QHY8

[blinky]

I decided to take a new set of BIAS frames, I do this once in a while and my last master BIAS was from 2015....  For some reason these ones look terrible and I'm a bit worried these is something wrong with the camera TBH.  I think I might have changed the OFFSET and GAIN a while ago so this was another reasons for raking a fresh set - do you think these are setup wrong and this could be the problem?

Here is a link to a BIAS frame, QHY8 taken with MAXIMDL 0s exposure... https://dl.dropboxusercontent.com/u/5236754/IC405-016BIAS.fit

Here is the previous one, comparing the 2 its easy to see the problem https://dl.dropboxusercontent.com/u/5236754/2ndNovember.fit

There appears to be a fixed noise pattern and if I make a master BIAS with a lot of these and use it in a stack the noise comes through in the image

[Oddsocks]

Looking at the fits header for the latest bias frame the CCD temp was 25 deg, cooling possibly not switched on? if so the resulting image is not so unusual.

Looking at the fits header for the earlier bias frame, history, it looks as though this was a PixInsight processed master bias so you can't directly compare the two.

Fits header for the newest bias frame posted below....

 

 

 

[blinky]

The QHY8 does not have a temp sensor 25 degrees is the default

[Oddsocks]

2 hours ago, blinky said:

The QHY8 does not have a temp sensor 25 degrees is the default

Well thats really useful..

Looking at and measuring the pixel values, your November master bias has a range from black to white of roughly 10 counts, the latest bias has a count spanning roughly 3700 so clearly something wrong, a normal bias pixel count from a cooled camera should be in single digits or low tens, not the thousands.

Could, be the cooling is not operating, possibly a power supply or amplifier problem etc, I doubt you could make that much difference by misadjusting the offset and gain but you could always reset to the factory recommended default values of Gain=50 Offset=120 and try a new bias, measure the max-min pixel values and see if they change, you can read these out directly from the mouse cursor position in PI or use Fits Liberator for a quick look if you don't want to mess around with PI.

I don't have a QHY8 and little experience other than the articles I have seen posted, I have read they have problems with the preset resistors on the amplifier boards going noisy due to oxidation but the articles I read referred to horizontal smearing, not changes to the pixel values, you could try mailing Berne at Modern Astronomy as he has a lot of experience with these cameras and may have seen this issue before, other than that you would need to contact QHY support unless another SGL member has seen this same problem.

 

[blinky]

You were corrrect!  My cooler cable had come loose!  Reseated it and now the BIAS is back to normal......  Thanks for your help with diagnosing the issue