My ASI6200mm is acting up again

CMOS Artifacts Troubleshooting
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Bruce Donzanti avatar
Bruce Donzanti avatar

I had an issue last night in that a perfectly round black dot appeared on individual frames hours after the ASI6200mm had been running at its usual settings: 100 gain at -5 degrees with the dew heater on. It did not look like the oval-shape black dot one sees when there is dew on the camera windows that eventually dissipates. The scope lens was clear, and the black dot was not filter dependent. Sky conditions were fine: clear, 65 degrees with no significant humidity. What is really odd is that the black dot shifted positions in various exposures and in some cases, there were two less intense black dots. Early in the evening the black dot was not present in all exposures, but it was present, and darker, in the exposures starting at around 2:30 am (humidity around 94% but not unusual for this area). Finally, when I turned everything off and started it back up, I did not see the black dot on any exposures I took. I am assuming the camera (which I had ZWO repair a few months ago for a bad board) is the culprit, but I am tossing it out here to seek other opinions.

Here is a screen shot of the last exposure.

📷 black dot.pngblack dot.png

Note: I just received a response from the ZWO US service center who replaced the main board back in November. They are not sure what this issue is but suggested to have the sensor board replaced.

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SonnyE avatar
SonnyE avatar

That looks like a significant problem to me. If it is still under warranty I’d get it back to ZWO US Service.

It does sound odd that A. It moves. and B. It went away when you cycled the power.

Good luck with it. If it were me, and out of warranty, I’d be shopping for a Non-ZWO camera. Then they are good they are very, very good. But when they are bad they are horrid. Personally, I’m moving away from ZWO.

So sorry to hear you are having repetitive problems with this camera.

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andrea tasselli avatar
andrea tasselli avatar
Bruce Donzanti:
I had an issue last night in that a perfectly round black dot appeared on individual frames hours after the ASI6200mm had been running at its usual settings: 100 gain at -5 degrees with the dew heater on. It did not look like the oval-shape black dot one sees when there is dew on the camera windows that eventually dissipates. The scope lens was clear, and the black dot was not filter dependent. Sky conditions were fine: clear, 65 degrees with no significant humidity. What is really odd is that the black dot shifted positions in various exposures and in some cases, there were two less intense black dots. Early in the evening the black dot was not present in all exposures, but it was present, and darker, in the exposures starting at around 2:30 am (humidity around 94% but not unusual for this area). Finally, when I turned everything off and started it back up, I did not see the black dot on any exposures I took. I am assuming the camera (which I had ZWO repair a few months ago for a bad board) is the culprit, but I am tossing it out here to seek other opinions.

Here is a screen shot of the last exposure.

📷 black dot.png

Note: I just received a response from the ZWO US service center who replaced the main board back in November. They are not sure what this issue is but suggested to have the sensor board replaced.

By the look of it seems like frosty patch on the sensor but I can't see at pixel scale so just tossing it.
Tony Gondola avatar
Tony Gondola avatar

Could it be something on your sensor window? I’d pull the image train apart and inspect just to be sure. I pulled mine apart of other reasons a few days ago and found a small leaf clinging to the side wall of my 2” Barlow, just waiting to pounce!

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Pete Bouras avatar
Pete Bouras avatar

Could be some debris that is moving around? I would inspect the FW and camera window carefully.

Is your 6200MM one of the new 2025+ model?

CS

Pete

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Bruce Donzanti avatar
Bruce Donzanti avatar

SonnyE · Mar 24, 2026, 01:50 PM

That looks like a significant problem to me. If it is still under warranty I’d get it back to ZWO US Service.

It does sound odd that A. It moves. and B. It went away when you cycled the power.

Good luck with it. If it were me, and out of warranty, I’d be shopping for a Non-ZWO camera. Then they are good they are very, very good. But when they are bad they are horrid. Personally, I’m moving away from ZWO.

So sorry to hear you are having repetitive problems with this camera.

Thanks. I’ve had ASI2600 (color and mono) and 6200 cameras, of which, two had to have new main boards put in after about 6 years of use in my observatory which is both temperature and humidity controlled. I tested a more expensive QHY camera a few years back- built much better than ZWO but I didn’t like the software.

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Bruce Donzanti avatar
Bruce Donzanti avatar

Tony Gondola · Mar 24, 2026, 03:14 PM

Could it be something on your sensor window? I’d pull the image train apart and inspect just to be sure. I pulled mine apart of other reasons a few days ago and found a small leaf clinging to the side wall of my 2” Barlow, just waiting to pounce!

I just took it apart as it is high up in my observatory and bolted to the filter wheel. All looks perfectly fine.

Bruce Donzanti avatar
Bruce Donzanti avatar

Pete Bouras · Mar 24, 2026, 03:42 PM

Could be some debris that is moving around? I would inspect the FW and camera window carefully.

Is your 6200MM one of the new 2025+ model?

CS

Pete

Hey Pete

Nothing moving around or loose.

Mine is an old one- almost 6 years old.

Rick Veregin avatar
Rick Veregin avatar

Hi Bruce

This is such an odd defect. It looks like the stars are normal through the spot, it is just the background level appears to be much lower than everywhere else. And I have never seen a spot that is just round and black, certainly not dust in your image train.

So this may be an odd thought, but since all other avenues are covered by others, one thing that might look like this is if the offset is not being applied in this round area, but everywhere else has the normal offset. This would definitely be something in the camera hardware, though unclear why it would happen. I’m pretty sure the offset voltage is applied at the back side of the sensor, so this would not be due to contamination on the front.

So when you see this problem I would look at a dark, is the spot there on your dark that is darker than everywhere else? Note that spot would still have hot pixels, but the general dark level would be different. I assume you use an offset, if not I would add one, or even increasing the offset might make it go away?

Rick

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SonnyE avatar
SonnyE avatar

Rick Veregin · Mar 25, 2026, 06:53 PM

Hi Bruce

This is such an odd defect. It looks like the stars are normal through the spot, it is just the background level appears to be much lower than everywhere else. And I have never seen a spot that is just round and black, certainly not dust in your image train.

So this may be an odd thought, but since all other avenues are covered by others, one thing that might look like this is if the offset is not being applied in this round area, but everywhere else has the normal offset. This would definitely be something in the camera hardware, though unclear why it would happen. I’m pretty sure the offset voltage is applied at the back side of the sensor, so this would not be due to contamination on the front.

So when you see this problem I would look at a dark, is the spot there on your dark that is darker than everywhere else? Note that spot would still have hot pixels, but the general dark level would be different. I assume you use an offset, if not I would add one, or even increasing the offset might make it go away?

Rick

On second thought Rick, maybe it’s a watermelon seed in the lens?

🤣