STL11000 - Horizontal banding w/either guider chip?

Hello all,

Both Internal & External guide chips for my STL11000 began exhibiting horizontal banding in the images. When tested at night, I am unable to discern guide stars in either chip's images, just banding. LEDs do not indicate any errors, but I tried swapping out a the PSU with my older/working 6303 PSU and see no difference.

Main imager functions flawlessly.

Are there any recommended troubleshooting tips?

Ive included FITS taken with CCDOps using each guider chip and both power supplies. These were taken in a dimly lit room without stars.

Thanks in advance!
Andrew

 

Thanks Colin,
I've completed the recommended steps and both bias and dark look OK to me (see attached FITS).
*Neither bias nor dark frame were taken in complete darkness (observatory venting lets in some light during day), but the banding is not visible.
The FITS attached previously above were all 1 sec. exposures, the FITS attached here were 0.12 and 3 sec for bias and dark respectively.
I have another RGH and extra cable I will try out this evening and report back...

 

Hmmmm, I've swapped RGH cables and re-shot bias and dark with both chips, banding is back.
Images attached.

Going to swap out RGH's now.

 

Using a different RGH has solved the "mystery" banding. (see attached)

Is the RGH a serviceable item or do I have a new paperweight?

 

Thanks Colin,
I am in the humid southeast US and plan on doing some "surgery" in the near future.
I bake desiccant plugs often...
Andrew