Problem with the ASI294MC sensor as indicated by flat frames

[alcol620]

Thanks again for your inputs. I have on 3 occasions cleaned the sensor as per the link that LandyJohn posted. Once when i took the old tablets out and dried them in the microwave, second when I dried them in a conventional oven and thirdly when I put new tablets in (after heating them in a conventional oven). If there had been moisture on the sensor I would have thought that my 3 attempts with dry tablets would have cured it. As symmetal suggests, maybe the camera is not sealed properly and allows dampness into the sensor area?

[Oddsocks]

 

On 24/09/2023 at 21:54, alcol620 said:

"For clarification when I talked about cleaning the sensor, I now realise that I was only cleaning the sensor window. I am not sure that I have a job description that includes removing the sensor window to get to the sensor itself!!

I mis-read your reply above and took that to mean you had only cleaned the camera window, not the sensor cover glass.

The sensor cover glass is hermetically sealed during fabrication, you can't remove that and the sensor would be damaged if you tried.

Just to clarify, did you wet clean or dry clean the sensor?

14 hours ago, alcol620 said:

"maybe the camera is not sealed properly and allows dampness into the sensor area?"

A way to answer that definitively is to try the following method.

Find a container just large enough to hold the camera upright and with about ten centimetres clearance above, such as a goldfish bowl, deep saucepan, cookie jar, etc.

The container needs to be only just big enough for the task, not too much empty space around the camera.

Cut three fingers of thin, but stiff, plastic, ca. 1cm x 5cm, from an old credit-card, or a supermarket plastic food tray and punch a hole close to one end in each of the pieces.

Use a couple of fresh in-car desiccant pouches, such as linked below, as bean-bags to support the camera, facing upwards, in the container.

https://www.amazon.co.uk/FiNeWaY-REUSABLE-DEHUMIDIFIER-MOISTURE-ABSORBER/dp/B077K8BJW4/

Add a few additional non-desiccant bean-bags, or similar, to support the camera firmly so that it can't tip over in the container.

Install new/regenerated desiccant tablets in the camera but leave the camera face-plate slightly loose and insert the three plastic fingers spaced equally around the flange area to keep open a slight gap, the punched holes in the plastic fingers should be outermost, do not pinch the face-plate screws tightly, you need to be able to slide the plastic fingers out of the gap easily.

Cover the container with clingfilm leaving a little slack, but otherwise sealed, and place the container/camera somewhere warm for 48hrs.

*see optional step for Argon purging below*

After 48hrs in a warm place carefully punch and push a thin-bladed screwdriver through the clingfilm cover over the container and using the holes you punched in the plastic fingers slide the fingers out of the flange area and then tighten down the flange while the clingfilm is still covering the container.

Remove the camera from the container and after fully tightening the flange screws immediately test the camera.

If the artefacts are still present after following the above steps then something else is going on with your camera, it can't be due to moisture.

If the artefacts were not present after the above steps but return after a few days/weeks then there is a leaky seal somewhere in the sensor chamber.

*Optional step: Argon purge*

If you want to Argon purge the camera you can do so by lifting a small piece of one corner of the cling-film cover slightly and inserting the thin feed pipe from a MIG/TIG Argon regulator and a disposable bottle of welding Argon, pushed down to the bottom of the container, and gently trickle in a stream of Argon at a very low rate for ten minutes.

The heavier-than-air Argon will slowly displace the damp air in the container through the lifted gap in clingfilm cover, leaving the container filled with almost pure and dry Argon. Then extract the Argon feed pipe, seal down the clingfilm and leave the container somewhere warm for twenty-four hours to allow any damp air trapped in the sensor cavity to be replaced with the heavier Argon and any remaining moisture to be absorbed by the desiccant pouches.

After twenty-four hours have elapsed follow the same procedure to seal down the sensor chamber as described above.

This method is not nearly as efficient as Argon low/hi pressure purging in a sealed environmental enclosure but it is almost as effective, and, comparatively inexpensive and easy to carry out a home.

Edited September 26, 2023 by Oddsocks
Spelling

[Oddsocks]

15 hours ago, Bukko said:

Following this thread with interest...

My 294MM has the same issue and cannot run it below 0c.

I have purchased new dessicant tablets and plan to change over in October. I am surprised that someone in the factory would think it OK to touch the chip surface and the QC team should be working hard to stop this from happening. So I now also need to clean the chip as well..

Anyway, my plan to open the camera includes using a glove bag - a large sealable bag with built in gloves. This is in an attempt to prevent unwanted dust getting inside. Also plan to use an argon purge so the dewpoint inside the bag should be lower than -50c, so at least I can start the new dessicant with a dry chamber.

If there is any interest, I will post the work here.

Gordon.

Hi Gordon.

Good to hear from you, hope you have recovered well from your health scare...

Your plan sounds good to me.

Only suggestion I have to make is to use a can of compressed air to blow away the dust from the outside of the camera, particularly around the cooling fins and fan aperture, and then wipe over the outside of the camera with an anti-static cloth (type used for vinyl records, CD's etc) before you place it in the gloved bag.

I do wonder if these SONY IMX sensors can be damaged by running at extremely low temperatures, the published SONY specification sheets available to the public are worthless in this respect as they have nothing to say about the acceptable operational temperature range.

Here at home I built a camera service and purging station from a second-hand acrylic fish tank, £2.50 from one of the SCOPE charity shops, round holes cut in the sides and nitrile-rubber gauntlet length gloves clamped into the holes using clamping rings made on a 3D printer, a rubber gasket glued to the top of the tank and another flat sheet of clear acrylic used as a lid. The whole thing cost less than £25.

"One day" I'll get around to fitting a Dyson type HEPA filter at one end of the tank and a suction fan, or vacuum cleaner hose adaptor at the other, at the moment I just vacuum clean the tank before I need to use it and get the camera inside quickly before more dust can blow inside.

At the Portuguese remote observatory we bought a second-hand laboratory clean-box for this purpose, about the size of a baby incubator. With a couple of dozen cameras and users out there that box is used frequently but being so large we do get through a 130 litre full-size bottle of welding Argon quite quickly, and at a couple of hundred Euros per bottle that adds quite a bit to our shared operating costs.

William.

[alcol620]

Hi William, I used the "Optical Wonder Fineoptical cleaning fluid" from Baader Planetarium.

[Oddsocks]

1 hour ago, alcol620 said:

Hi William, I used the "Optical Wonder Fineoptical cleaning fluid" from Baader Planetarium.

That should probably be ok, unfortunately Baader are rather cagey about what exactly goes into that product and they don’t publish a hazchem leaflet but they mention alcohol in their Q&A section so most likely its just a mix of Isopropyl Alcohol, deionised water and detergent, which is safe enough for cleaning lenses, mirrors and the AR cover-glass on most CCD and CMOS sensors.

Sony don’t publish any useful information for consumers about how to clean their sensors and have always been rather secretive in this area however other manufacturers are more helpful and this OnSemi document gives very clear guidance on the types of chemicals that can be used and the recommended methods (see page 3/4).

The most common mistake when cleaning a cooled camera sensor is to spray the cleaner fluid onto the cover glass and make it too wet, the cleaner fluid should be sprayed lightly onto the cleaning swab/spatula and if as you drag the swab/spatula across the surface of the cover glass it leaves a trail of droplets behind then you’ve used too much liquid.

Not all types of contaminants can be removed with alcohol.
Silicone oil that is typically used as a component of heat-sink compounds for the interface between the TEC cold-finger and the back of the sensor package is particularly difficult to clean away and if that gets on the cover-glass it requires chemical solvent cleaners that are both toxic and capable of damaging the AR coating on the cover-glass, as well as possibly dissolving the glue that bonds the cover-glass to the sensor package. If silicone oil ever does contaminate the cover-glass it’s best to have the camera professionally cleaned unless you have some experience of handling hazardous chemicals and can be sure which materials have been used in constructing the sensor package.

The work you have carried out should have made some improvement and I can’t think of anything else practical to suggest beyond the contributions already made to this thread.

Have you tried opening a case on the camera manufacturers support forum, or emailing the retailer you bought the camera from to see if they have any previous experience of this problem?

I’ll keep watching your thread and reply back if I think of anything new but right now I’m out of fresh ideas.

William.

 

[alcol620]

Thanks William. I had an exchange of information with ZWO tech and they initially suggested the usual "moisture in the works" and dry it out. Later it was suggested get in touch with the retailer and get it sent back for repair. i bought the camera in a used condition so my optiona are limited. It worked fine over a period of months so I had no come backs on the seller, just my bad luck. I saw mention on another site to use dew heater on the camera to prevent moiture, but I ssume that this would only stop the camera outside glass from dewing up.

[symmetal]

On 01/10/2023 at 22:50, alcol620 said:

I saw mention on another site to use dew heater on the camera to prevent moiture, but I ssume that this would only stop the camera outside glass from dewing up.

Yes, that's right. The ASI294 doesn't have a heated protect window so if there was a dew issue with the window, getting the Zwo camera heater strip would help. This won't affect dew on the sensor itself like you have.

Edited October 3, 2023 by symmetal