STL 11k Cooling range -20° maxi

Hi,

I have not used my STL11k for about 5 years. I have re-installed it this week and get an issue with its CCD cooling.

With an outside temperature at about 15°C, I can hardly reach -5°C CCD tempearture. Mores exactly -4,5°C with 100% power.

I remember that 5 years ago, the cooling performance was already below specifications, but not to that extend.

My question is : Is there any way to "repair" or adjust the cooling by myself ?(do not want to send the CCD for repair, would cost me too much)

Regards
Franck

 

Franck,

Hopefully, it is only a problem of a defective thermal sensor. Compare a series of Dark Frames, (even in-house or on scope, in the daytime) - as the cooling starts up. If there is no significant improvement between Darks, then it may not be a false reading from the thermometer. Don't know how to test if it is a defective regulator, that is limiting the process. You would think that if it can regulate from room temperature down to -5C, then it is perhaps working properly. A test might be to compare the Darks Test, starting at even higher than normal day/room temperatures, and see if the regulation "Range" is about the same. If so, that might suggest that it is working, but just can't reach the lowest limits, due to bad or dirty heat sink thermal surface contact.

Then, I wonder if the only problem is that the "thermal grease compound" has dried up & its bond cracked up like dry lake bed, in the intervening years. If the actual TEM module is still good - and there seems little reason for a semiconductor designed for such thermal extremes to fail - then it should be easy to remove and re-grease the heat sink yourself, or perhaps, by removing the cover beforehand, by a tech in a PC repair shop. They do that cleanup & re-grease for overheating PC processor chips' heat sinks. That would be a very quick and inexpensive local repair, for a test. If you do that, try to buy the best PC Processor thermal grease, with superior thermal conduction properties. The size and high (egg-frying) temperatures of processors, is comparable to what the CCD sensor would have to handle.

Otherwise, save yourself much time and effort, and send it in. The added benefit will be that it might also get an overall "health check", firmware update, and maybe any later engineering fixes or improvements installed by repair professionals like Bill Lynch at SBIG support.

The STL is still among the the best astro cameras, built well & designed proudly in the USA - worth maintaining for another decade of good service.

Joe Z.

 

I could be filled with moisture as well. I would bake the desiccant out and try again.
Are you sure you are using the right power brick.

Make sure to run the test with the power brick going straight to the camera, not though the mount as well.
ESD can quickly ruin the CCD. Unless you are setup to work with CCD's I would not pull the CCD.

Joe has a point, you could have a bad thermistor, compare darks.

 

Good point Tim,

I thought that the CCD heat sink could be separated by itself - as they do, with say Intel Processor chips - without actually "removing" the chip itself, and breaking the seal on its front chamber. I wouldn't want to go any further than that.

Joe Z.

 

Hi Franck,

Just one more thought. You say cooling wasn't that great even 5 years ago. Have you checked the fan?
If it isn't able to run at full speed, the TEM won't be able to extract as much heat.

Its motor may be struggling with an accumulation of dust - especially if it operated in a desert environment. The fan would have sucked in a lot of dust & fine sand which may have clogged the motor spindle, unseen under the blades. I had that happen with my RCOS TCC electronics cooler. The STL logic won't be able to notice & report this. Bugs will do the same, though not as badly. Last week I found a long deceased bug, stuck under my fan blades, which I missed in my several years of use.

It is easy to remove the back cover, (careful not to kink the internal water hoses), to check the for any "dust dunes" between IC pins and around the fan, & just blow it out. Give the fan a gentle spin, to make sure its bobbin coasts smoothly.

Might also be worth checking which way the fan blows - into or out of the camera. Sometimes a previous owner could have done a repair, and reversed the DC wires - the fan spins, but the blades deflect rather than cup the air, so it cools inefficiently. The guy may also have replaced the fan mechanically backward. There was an SBIG group discussion years ago, whether the STL fan should be mounted to blow inward, directly onto the heat sink, or outward. If the latter, the fan would draw air from the more distant narrow slots with the air stream losing force by the time it gets to the heat sink. Blowing inward, there would be the added benefit of the Venturi effect impacting the heat sink directly, with much more cooling, before the warmed air escapes to the side slots.
Would be interesting to get the official SBIG statement on "fan air direction" here.

Finally, going back to my reply about checking "Cooling temperature Range", at two different high temperature starting points. You might try putting the entire STL into the kitchen "freezer", simulating a +4C winter night, and close the door on the data/power cables. Observe the temperature regulation on a laptop, and check that the RANGE ( 40C ambient delta ?) reaches specification, in which case the regulator and likely the thermistor may be fine. If the STL does reach its range spec, then it might have been the fan, or even something (loose wires ?), interfering with the fan blades themselves.

Just a thought. Hope this might - in a pinch - help you remedy the problem yourself, without time lost in shipping.
Joe Z.

 

Thanks Bill,

For correcting what I had posted. Of course, you are absolutely right. Too bad the task, if it would have been the TEM, isn't easy to service. Hopefully, the problem is somewhere else and much easier to fix.

Joe Z.

 

Hi ,

First, thanks all for your analysis and suggestions.

I will not go the route of de-assembling the CCD myself. By "doing it myself", was more thinking about a possible electronic adjustment.

I have something new / different to share with you. Yesterday, as I re-installed / updated the PC various softwares, I took the time to updade the SBIG drivers as well, to their latest version. And surprisingly, that changed a lot the cooling result:

Ambient temp was 17°C. At 100% power , the CCD cooled down to -11°c. So a delta of 28°C. This is 8°C better than the previous tries. But is it within the spec ? (I assume not, that is still too low right)

I mentionned in my first post above that I remember that 5 years ago, the cooling performance was already no very impressive. I think it was close to this -28°C delta. I was already considering the need for a repair.

If you have time to read :
This STL has a long history. When received new, she was severely suffering from the famous vertical banding. So she was send, complete, with its filter wheel and 7 Astrodon filters for adjustment at your reseller Astro Unterlinden during the visit of an SBIG technicien. The adjustement improved (a bit) the vertical banding but did not completly corrected it. To the point that narrow band imaging at binning 2x2 was/is fairly impossible.
So, during the next six months I did mostly LRGB acquisitions. But got extreme trouble to create balanced RGB images. This was a terrible time during which I did not produce one single correct image.
Until one day, while cleaning the filter wheel, a friend of me noticed that the RGB filter were not Astrodon filters but from another unknown brand.
I have had hard time to believe it and long discussions between Astro Unterlinden, Astrodon and the initial CCD/filters reseller (was Galilleo in Swizterland). Was impossible to determine what happened and when. It ended by Galileo to replace the RGB filters by real Astrodon filters and Don (Astrodon) to absorbe a big part if not all the cost.
I also remember (but I'm less sure), that the cooling limit issue was not noticed prior this repair event.
Then I got sick, have had to change my job and finally started my own business. Was so busy and so frustrated about the last six month of imaging, that I put astro imaging apart for while (well, many years in fact). My company is now stable and time is back for imaging again...

I took the time to writte this story to explain that yes this CCD had been "repaired" by somebody else. So the eventuality of the fan flow being inverted is not null. Will definitively check it (and clean it if needed).

About the power. The AC/DC converter is the original SBIG one. It goes to the CCD using one of the internal cable routed inside the ME (connected to the back and up panels). Will give a try without the extension, but will need it anyway in real usage time.

With also regenerate the dessicant, just to try this other possibility, but I'm less confident about this possible cause.

Will come back after all this has been explored. If it ended to be another cause, will contact you Bill.

Regards
Franck

 

Making progresses but not yet there...

Easiest try, I connected the CCD straight to its DC adapter :

Temp starting point after CCD was connected : +18°C
100% of cooling power turn on
Waited about 10 min : it reached -16,9°C

So a delta of 35.4°C Looks much better !
I took one picture (1min), to check that the temp was not increasing. Was still ok.
BUT I leaved it in that stage for about 30 min, power still at 100% and now that I'm back I can see that it is at -11°C, so it lost 6°C .

A delta of 35°C is good (even better as the official spec is 32°C without water cooling), but what could explained this 6°C lost (delta of only 29°C, 3°C out of specs) ?
(the obs roof is closed and the PC is inside the obs, but I doubt it could have changed the ambiant temp by +6°. I may need to put a sensor in the obs or the CCD in the fridge as suggested to compare apples and apples).

Futher experiment:

From this 100% power -11°C stage, I turned off the fan. I could see the temp increasing progressively by a few degrees. So it is "acting" (not yet checked its flow orientation and clean stage).

From there, I turned off the cooling. I can see the CCD temp going up till it stabilized around 29°C (without taking any image). This is about 11°C above ambient temp. Is this "normal" ?

More... I reconnected the extension DC cable, re-connected the CCD and restarted the cooling with a -50° target, at 100%. Guess what, it cooled down till about -11° , again...

Not sure yet what to conclude at that point, but the delta looks the same with or without the alim extension cable and is limited to about 28° vs the ambiant temp...

Regards
Franck

 

Hi,

As mentionned the above experiences were done in the closed obs (is raining currently), with the PC running inside. So there was not a good air flow and the air temp around the camera probably increased a bit.

So you are probably right Bill and I will wait for good weather to redo the experiment once the obs roof is opened.

Worth mentionning additionnaly : yesterday when I turned off the power in the obs, I visualy checked the ccd fan. It is cleaned. BUT i noticed the security attachment (nylon tie up) of the ccd was passing twice in front of the fan. This is a small tie up, but anyway is not helping the air flow and I will move it away.

Today will open the back of the ccd, regenerate the desiccant (needed anyway), and check the air flow direction.

Thanks again to all for your support...

Regards
Franck

 

Follow up, I removed the back cover to check the fan:

The air flow was going from the inside to the outside of the ccd.

Obsv: This cannot be done by mistake, the connector cannot be inverted (the second pin is cutted on the 4 pins connector) and the fan itself cannot be mounted in the other side without some slight mecanical modification (the screw have V heads and the fan has V hole on one face only).

Anyway, I have inverted the fan (I made some V holes to it on the other side).

Turned on the CCD, initial temp was 22.7°C. Turn on the cooling at 100% to -50%, with the fan turned on.
The temp went down till -18.2
So a delta of 40.9°C (probably more close to 35 versus ambiant)

About stabilisation : I opened the door of the obs and changed to target temp to -17° It is currently trying to maintain it. The power evolves between 94% and 98% for about 10 min now. Looks ok.

15min later : the power increased to 100% to maintain the -17v target. And now see the temp to start to increase (-16.9, -16.8,-16,5...) This is less good...

Will probably hase to set a temp target about 5° above the minimum it can reached.

Note: with the power extension cable in place, the 11v yellow led is turned on, indicating the voltage dropped below 11v (but above 10v as the 10v led is off). From the technical document, this should not prevent the cooling system to work properly, right ?

Rgds
Franck

 

Hi all,

Bill as I read you, I'm doing my first lights on real sky.

Outside temp is about 15°c and the CCD is running at -20° for about an hour, at 66% of power. Fine enough for me.

At the end I'm not sure what was limiting so much the cooling the first days, but anyway we can close this topic.

Thanks again for assistance.

Rgds
Franck

 

Hi Franck,

A couple of points I just thought of, even though you intended to close the thread.

First ... I think that the temperature change will be different if you test while NOT imaging a target., than when you are actually doing long exposures, perhaps even short one minute ones. The reason is that the CCD chip heats up when it is recording, and the longer it does, the more heat it generates, which makes regulation slightly more difficult, depending on observatory/camera ambient temperature and air flow. Then if you take many sub-exposures, each very long, and for an hour or so, the sensor never cools off. Otherwise, just testing the camera without actually imaging, you should see better temperature performance, since the sensor is not generating any heat - i.e. you are cooling an already cold chip.

Second ... I too had a problem setting up my STL-11000 power supply on the scope. Originally, I wanted to use the SBIG power brick, for convenience, but discovered I was just a few feet short of power cord on the DC side. That would mean I would have to attach the brick up higher on the pier, to give the mount enough cable "stretch slack" as it moved around the sky. My power setup is in a sealed plastic electrical box on the ground.

The solution was to use the SBIG DC (battery) power cord and simply plug its cigarette light plug into one of my other available DC power supply (expander) sockets. This was better because the standard STL power brick only has a 12 foot DC cord, but the SBIG battery cord is 16 feet long. The 4-foot extra length was just enough extension for my setup, without wasting power in another extension cord itself, as well as in their extra connectors.

You are using an "extension cord" to send SBIG power "through" your Software Bisque ME mount. It looks like the extension is too long, in addition to the original cord. This causes a voltage drop and power lost in the cord extension itself. So, you get the borderline 10 vdc yellow LED warning. The solution is either make a "sufficient length" power cord using the next thicker gage "very-many-stranded" wire, or try the (optional) SBIG DC cable - if the extra 3 or 4 feet would be enough for you, compared to the (AC/DC Brick) shorter DC-side cable.

Joe Z.

 

Bill,

I base my comments, on observing the temperature info recorded in the image file EXIF data, from my Canon 50D and other DSLR's, with no cooling. I have seen significant temperature changes between exposures, especially long ones. I don't think the STL sensor behaves any different. I suppose SBIG has graphed data on sensor heating versus exposure time.

No disservice intended.

Joe