Help! ASI224MC-C noise that seems impossible to remove

rgbtxus

I bought an ASI224MC-C to begin exploring planetary imaging and I gave it a try last night on M14 figuring since it was cooled I could use it on DSOs too and had horrible pattern noise that appears difficult if not impossible to remove. See attached (gain 135, 0ffset 10, gamma 50, 15 sec, T -14.6˚C). I am at a loss for the cause. Changing TEC power from a lab PSU set at 13.5 +/- 0.05V to a battery and then just removing it had no effect (cooler is speced to eat 9-15V). Neither did removing AC from the laptop. The USB cable went straight to the laptop and not through a hub. Just to rule more things out I removed the LPS-D1 filter and then the 0.8x reducer so I just had the camera directly attached to the focuser and the noise pattern persisted. There were no clouds in the sky that I could see. Finally trying different gains (0, 135, 300, 450) did not remove the pattern, neither did increasing exposure until the upper 2 sigma point of the curve was well above 50%. Any thoughts? I saw something similar in my ASI174MM-C at 0 gain, but raising the gain removed the awful noise pattern. Here the pattern persisted to the highest gain I tried , 450IIRC)

rgbtxus

Ok, it is frost! I ran the unit for an hour at -15˚C and then inspected the sensor under magnification and bright light. There is clearly moisture/frost on the surface of the sensor. This unit arrived in early May and travel meant I did not get to test it until now. So, this is new unused unit that clearly has moisture in the imaging chamber. Since there are supposedly desiccant tabs in the cell to remove moisture from the air inside, it must be that the chamber was not sealed and the desiccant tabs have been trying to absorb all the moisture from the Texas summer. The unit came with extra desiccant tabs which are in a foil seals container, but if I am reading the indicator properly (light pink), then those may be no good. I guess I need to contact customer service since I think I am past OPTs return window. This means the last three ZWO cameras I received were all defective in some way. Very frustrating!

Sam@ZWO

I suggest you can exchange the desiccant tabs in the package

the indicator is for humanity 8%, very critical actually

so it should be still useful for you

then let's see how long it can last

rgbtxus

Hi Sam,

I replaced the desiccant tabs. While doing so I gently heated the chamber (120˚F) to reduce moisture for 10 minutes and then tightened it down. Initial tests suggest that the frost/condensation problem has been resolved -- at least for now. I could not tell if the o-ring was making adequate contact when I reassembled it. Would it be wise to pick up some vacuum grease and apply it to the o-ring? Since I needed to replace the tabs immediately on a new unit, it would be great if ZWO could send me a replacement package.

Thanks for your help,

Richard

Sam@ZWO

yes, very few vacuum grease would be better

no problem, we will send you a new unit, just contact us through email