This thread may be of interest to you.........
https://www.eevblog.com/forum/thermal-imaging/thermal-camera-purchasing-the-perils-of-buying-a-cooled-camera/When a Rotary Stirling Cooler fails it usually either sounds pretty normal but never achieves operating temperature at the cold finger, or it sounds like a tin can full of bolts being shaken
Rarely have I seen much in between these two states in terms of failure. In your case I would suspect that you are actually experiencing piston lock rather than bearing or flexture failure. The Pistons are precision parts and run in a very pure Helium environment that will not freeze at the intended operating temperature. If the Helium fill has been lost through leakage past a seal or deliberate act, then the cooler can contain atmosphere or pollutants and that gas environment can very easily freeze causing the pistons to become locked in their cylinders.
Are such coolers repairable ? Yes, but at very high cost. Something around $10K by a manufacturer. Remember that the imaging array is integrated into the coolers cold finger Dewar so either the original cooler must be rebuilt or a new/rebuilt cooler bought from the camera manufacturer. Both are very expensive options.
Can a Stirling Cooler be DIY rebuilt ? In my opinion, no. Such a rebuild would be beyond most home workshops as these really are very high precision items and are normally rebuilt in conditions similar to a hard disk construction or repair lab. To truly rebuild such a cooler, all worn parts are changed, all new specialist soft metal seals are replaced (Helium seals are specialist metals) and finally the Helium Gas must be introduced to the cooler and the sealing plug fitted without any Helium gas contamination occurring. That includes the presence of atmosphere in the housing before fill or any lubricants that would contaminate the gas fill or freeze at 77K. Not a DIY job.
Can a cooler be just refilled with Helium gas ? Yes but with caveats ....
1. The Cause of the Helium gas loss must be addressed or the new gas fill will escape.
2. The Helium gas is specialist Ultra High Purity Helium and not just “Balloon Helium”. Any contamination of the gas with atmosphere or pollutants can lead to freezing and piston lock, just as you are already experiencing !
3. The atmosphere within the cooler should be purged to remove any contaminants in preparation for the Helium gas fill.
4. Special fittings and tools are required to use the coolers fill port and seal it after filling.
5. Specialist soft metal gas seals are used in the cooler, including a single use (non reusable) seal on the fill plug. A new fill port seal will be required.
6. Even those who have addressed the above issues have found the process a complete failure. A cooler may have suffered wear or failure that cannot be seen without a complete rebuild. Basically, you are taking a risk spending money on a re-gas without a full cooler rebuild.
Fraser