Something a little different - FLIR Cooled weapon sight & recon scope - MIRV - Page 1
Forum section: electronics / general

author: Fraser
author_rank: Super Contributor
timestamp: June 26, 2025, 03:15:52 pm
content: And now for something a little different…….I recently stumbled upon an auction for two “faulty” FLIR Stirling cooled thermal weapon/recon surveillance scopes and the BIN asking price could not be ignored. Looking closer at the two scopes, I recognised them as AN/PAS21, or a variant of such. I thought the long lenses were missing but then saw the picture revealing that these particular units are fitted with 30mm lenses. Likely for surveillance work.The two scopes were advertised as the “FLIR See Spot III” which would make their military designation AN/PAS21, as I thought. The ID plate on the units confirms that they are the See Spot III chassis. But here is where there is a twist in the tale. The See Spot III gains it name from the fact that it is designed to see two bands, 4.5um to 4.8um and 1.06um. This makes it a MWIR-SWIR hybrid scope. The 1.06um coverage is to enable the See Scope III to image the Target Acquisition Systems that use 1.06um lasers. Interesting stuff, but not much use to me ! Further digging revealed the units that I have purchased are not the conventional See Spot III, but the MWIR 3.0 to 5.0um MIRV modelThis is far more useful in civilian environmentsThe FLIR MIRV is a “Miniature Infrared Viewer” that may be used for surveillance or as a weapon sight. It uses a Stirling cooled 256x256 pixel InSb FPA and has a low NETD of 20mK. When equipped with a long lens, these units can quite literally see for miles with low noise and good clarity ! My purchases have a more useful 30mm lens that still provides quite a narrow 14.5 Degrees HFOV, but not as extreme as the 2.75 Degree HFOV 150mm or 1.75 Degree HFOV 250mm lenses. The MIRV uses a high resolution LCD EVF and provides an NTSC video output for a larger display or image capture. The cooler is a conventional FLIR rotary type, likely to be a MC3 or MC3LP model. These have an MTBF of 8K or 12K hours, depending upon exact model. There is a chance that the coolers in the units that I have purchased will still work as they were made in 2007. There is also the very real possibility that the coolers will be dead or that the MIRV’s have been “decommissioned”, if they were previously in military use. Buying the two units was a calculated risk on my part, but the price was too good to miss, so my resolve to stop buying thermal kit weakened and I bought themThe scopes use an unusual power source, namely a “D” size Lithium 3.6V non-rechargeable cell. These cells are a common commercial type, but expensive ! The scopes power consumption is 4.5W and the run time on the Lithium cell is only 5.5 hours. My units are supplied with their optional vehicle mount power adapters that convert 6V to 28V does to 4V and these mount in place of the Lithium battery. This provides me with a good choice of power sources for these cameras…. if they can be repaired !My purchases will need some TLC and investigation into whether they are truly faulty, and if so, what has failed in them. If the coolers are dead, they will be interesting paperweights that I may sell to appropriate collectors as they appear to be quite rare. If it is an electronics fault, I have a chance of repairing one, or both of the units. I will be replacing the missing rubber eye cups and objective lens caps.These units will not win any beauty contests and are basically shaped like a brick ! They are ruggedised and use large controls to make them suitable for harsh environments and gloved hands. In this respect, they are similar to the fire fighting cameras that I collect. There is no place for fiddly controls on such specialist equipment.The units are due to arrive in the next couple of days so watch this space for updatesFraser

author: Fraser
author_rank: Super Contributor
timestamp: June 26, 2025, 03:25:58 pm
content: Some pictures borrowed from a web page that details the AN/PAS21 See Spot III cameraWeb page url……https://www.thefirearmblog.com/blog/2023/05/26/flir-see-spot-iii/These images belong to the above web page owner.Note that the lens is removable to install different lens types. My MIRV’s similarly have removable lenses.

author: Fraser
author_rank: Super Contributor
timestamp: June 26, 2025, 03:30:30 pm
content: Some imagery captured by the above referenced See Spot III scope. The range of that unit with its long lens is impressive. Note the lack of noise in the images. This is not just good image processing, it is the result of a lovely low noise FPA operating at -196 Celsius (77 Kelvin).The reticle type may be changed or even removed from the scene and there is digital user positioning of the reticle using a joystick under a protective cover.The little hut is viewed from a distance of 1530 Yards (0.87 Miles / 1399 Metres) with the 250mm lens and then with the x2.5 supplemental lens fitted. There is a country scene with some white “blobs” near the bottom. These are cows viewed at a distance of 3200 yards (1.8 Miles / 2926 Metres). Another picture of the cows is captured after a x2.5 supplemental lens is added to the front of the 250mm lens. The Owl image is taken from 72 Yards (66 Metres) distance with the 250mm lens and then with the x2.5 supplemental lens fitted.

author: Fraser
author_rank: Super Contributor
timestamp: June 26, 2025, 03:41:55 pm
content: The data sheets for the See Spot III, MIRV and SNIPIR models

author: Fraser
author_rank: Super Contributor
timestamp: June 26, 2025, 03:43:05 pm
content: A likely candidate for the cooler used in the MIRV, the FLIR MC3 or MC3LP

author: Fraser
author_rank: Super Contributor
timestamp: June 27, 2025, 11:45:43 am
content: The two thermal scopes arrived a few minutes ago. It is hard to judge their size until you have it in your own hands….. these units are smaller than I expected and very neat There is already some “weirdness” with regard to the DC-DC power adapters that are with the units.One feels lighter than the other and has something rattling around inside it…..I suspect it is empty. The other has a US 110V power plug connected to itI will do some tests on the scopes later to see if there are any signs of life. If I am VERY lucky, it will be the power adapters that are dead rather than the scopes, but historically, I am not that luckyFraser

author: Fraser
author_rank: Super Contributor
timestamp: June 27, 2025, 01:27:55 pm
content: Well this is one of those OMG moments when you realise that someone has connected a low voltage DC device to the mains supply and things have gone BANG !Yep someone has seen the black and white wire colours on the 6V to 28V input DC-DC converter module and thought it was a mains adapter so connected it to either 110V or 220V. There is a US 110V type plug still connected to one of the adapters. Needless to say the adapters are TOASTNow the likelihood of these adapters being installed in the scopes when this craziness occurred is high, so I need to investigate how much damage has been done to the scope DC supplies. One scope does start and the cooler runs. The other tries to start, the cooler runs briefly but the scope then shuts down with an excessive current draw.Oh what a mess. Such an over-voltage event has the ability to completely destroy both of these scopes so they may well be FUBAR.

author: Fraser
author_rank: Super Contributor
timestamp: June 27, 2025, 10:33:17 pm
content: One thermal scope repaired. It had a failed capacitor on the DC input. Now working on the second scope that thinks it is at operating temperature as soon as it is switched on. I will likely produce a teardown post on these MIRV scopes. They are very nicely made with high quality components evident throughout.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: June 27, 2025, 11:03:48 pm
content: The "Proof of life" on the first MIRV scope. I used an external service monitor for ease but include a picture of the EVF. It displays the image in the green spectrum to preserve night vision.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: June 28, 2025, 12:32:37 am
content: The second MIRV has been stripped down in order to test its two PCB’s . Both PCB’s are in full working order.At first switch on the cooler should run at high revs for around 6 minutes until 77K is achieved at the InSb detector. Once this is achieved the cooler motor should slow down and operate in the “maintain 77K” mode. The fault on the second scope is that it immediately enters the “maintain” temperature mode as soon as it is switched on.The driver board for the Stirling cooler appears to think that the 77K operating temperature has been achieved, even when it has not. The PCB itself tested OK in the repaired unit so it is being fed incorrect information from the Stirling cooler/InSb detector assembly.From memory there is a temperature sensor on the InSb detector die that comes out to pins around the detector dewar. In the MIRV there is a small PCB connected to the pins around the Dewar that has some components on it. I shall investigate the various wires coming off of that PCB to identify the temperature sensor feed to the Cooler driver. I do not believe this to be a failure in the Cooler motor itself as the MIRV uses the InSb temperature to control when the LCD display is switched on and when the cooler speed needs to be reduced to its “maintain” speed. I am seeing the LCD switch on as soon as power is applied, which should not occur. An interesting little fault. If the temperature sensor itself has failed, I will have to consider options to spoof the signal sent to the cooler and LCD display controllers.Fraser

author: ArsenioDev
author_rank: Frequent Contributor
timestamp: June 28, 2025, 02:46:29 am
content: Quote from: Fraser on June 28, 2025, 12:32:37 amMost often they use a bandgap diode that has a wicked tempco to get a die temperature, very common method used all over the semicon industry. a very gentle diode check on the temperature sensor should tell you if it's blown or just not making it to the temp sense circuit(which may have failed)

author: Fraser
author_rank: Super Contributor
timestamp: June 28, 2025, 10:32:52 am
content: Arseniodev,Thank you for this information. I suspected a diode might be used but was considering how to test it as I am unsure whether it could be harmed by a simple diode check on my a Fluke 87 III or my Peak Atlas Component Analyzer. I will treat it with great care as I do not want to damage its junction characteristics.Hopefully one of the components on the small PCB mounted around the dewar is responsible for the fault. I will reverse engineer that PCB and use the working MIRV as a reference for tests. Rather than directly stimulate the temperature sensor diode, I will use the circuit that normally drives it to determine whether the diode has failed or the driver circuit has an issue. Both main PCB’s tested OK so the fault has to be located on the small Dewar PCB or the diode itself. If the diode has failed, I am hoping that there is a second diode present that may be used. Some FPA’s have two temperature sensing diodes. Diode failure seems unlikely but we shall see.Thank you again for the comment. You confirmed that I need to be gentle with the temperature sensing diodeFraser

author: Bill W
author_rank: Super Contributor
timestamp: June 28, 2025, 10:59:10 am
content: Quote from: Fraser on June 27, 2025, 01:27:55 pmGlad the main units survived. On the plus side you do have all the necessary mechanics of the DC adapters - far trickier to replicate than a DC input.it may be worth adding that Lithium D primary were a preferred power source for military kit back then. Well before high capacity rechargeables or LiFeSO4 primary emerged and the Li primary could deliver decent starting surge currents even when cold compared to NiMH or alkaline cells.If all else fails, put a short across them and they become a free hand grenade !Bill

author: Fraser
author_rank: Super Contributor
timestamp: June 28, 2025, 11:08:02 am
content: Detail of the PCB that surrounds the Dewar. I shall reverse engineer it as far as possible but without the pinout of the detector connections I am working in the dark. The IC's may provide me with the information I need to determine which components are involved in the temperature sensing function. I am hoping to avoid removing the cooler from the chassis as there is reasonable access to the PCB in-situ.AD8031 - 2.7 V, 800 µA, 80 MHz Rail-to-Rail I/O Single AmplifierA86U - Unknown identity at this timeFraser

author: Fraser
author_rank: Super Contributor
timestamp: June 28, 2025, 11:39:33 am
content: Bill,I am now of the view that one power adapter was plugged into the mains whilst not installed in the scope or the scope was switched off at the moment of the explosion. Thankfully these scopes use a nice solid physical switch in the power feed from the battery bay to the power PCB. The adapter would have exploded the moment it was plugged in and I have checked the output TVS protection diode, it measures 7 Ohms. Thankfully the mains voltage did not get through to the scopes electronicsOne adapter, the one with the mains plug fitted, is completely fried and will require a complete rebuild. The other appears to have suffered a natural death through the failure of one of the output capacitors that then desoldered itself from the PCB ! The adapter works fine when connected to 12V and provides the correct 4V outputThe fried adapter uses the LTC1159 switcher IC that drives two external MOSFETS. The high side MOSFET exploded and would likely have passed the mains voltage to the output capacitors and TVS diode. Hence the PCB burn marks around the output capacitors. I also noted PCB burn marks around the DC input to the PCB where the mains voltage flashed across to the PCB ground pourThe PCB design includes a bridge rectifier at the DC input and I suspect someone saw this and though the adapter was one of those clever transformerless Mains to low voltage types that use a mains switcher IC to lower the voltage. I count myself fortunate that neither thermal scope got fried.The current draw of the scopes from a 3.6V supply is 1.7A whilst in cool down mode (duration 6 minutes) and 1.3A when operating normally in temperature maintenance mode.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: June 28, 2025, 12:25:04 pm
content: I will add the MIRV teardown pictures to this thread today in case such is of interest to readers. The MIRV may be an ‘ugly duckling’ on the outside, but it’s internals are very nice, as is to be expected on military grade equipment. The MIRV does not have a civilian version, unlike some other NATO thermal scopes. It was designed from the ground up for military use.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: June 28, 2025, 02:41:48 pm
content: Time for the pictures taken during the teardown.The aluminium side covers are held in place by a multitude of socket head screws. Once these have been removed the side covers lift away to reveal the PCB's behind. The side covers contain a recessed gasket to provide weather protection.Once the side covers have been removed two PCB's become visible. These are secured in place with 4 screws per PCB. the PCB's are easily lifted away once the retaining screws have been removed, but care is need with the processor PCB to avoid stressing the LCD EVF ribbon cable. A cables are securely locked into the PCB connectors and the cable loom is well managed with lacing used in some areas. The rear of the controls reveal the use of high quality components.With the two PCB's removed, the Stirling Cooler and optical block are revealed. The Stirling cooler has a small PCB mounted on its connections around the Dewar. The scope chassis cannot be disassembled further to provide better access to the cooler. The optical block mates with the detector housing and the lens focus mechanism is visible adjacent to it. The lens system in the MIRV uses a moveable focus lens in the camera mount and a removable lens assembly that may be selected for the required application. The focus mechanism is high quality.On with the pictures......

author: Fraser
author_rank: Super Contributor
timestamp: June 28, 2025, 02:45:25 pm
content: Pictures continued....The final picture shows the current draw by the MIRV during the initial 6 minute cool-down period. Once the operating temperature of 77K is reached, the cooler reduces speed and the current consumption reduces to 1.3A from the 3.6V supply.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: June 28, 2025, 03:12:48 pm
content: Pictures of the destroyed DC-DC power adapter. This takes 6V to 28V and buck converts it down to 4V for the thermal scope. Feeding AC mains voltages into such a unit is not recommendedI have repeated the schematic diagram of the LTC1159 here to add clarity to the adapter design.

author: Fraser
author_rank: Super Contributor
timestamp: June 28, 2025, 03:58:46 pm
content: Regarding testing of the InSb detector temperature sensing diode…..Some time ago I bought a Cryogenic temperatures thermometer that uses a cryogenic diode as the sensor. I thought it might be useful one dayThat day may have arrived if I need to safely test the InSb detector die diode or look for a “spare” diode on the pinout without risk to the diodes junction characteristics. This thermometer is a specialist bit of kit designed specifically for very expensive cryogenic temperature sensing diodes.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: June 28, 2025, 06:26:26 pm
content: Well the diagnosis was simpler on the second scope than I had expected.I had my suspicions that the black and blue wires connecting the detector PCB to the cooler control PCB might be the temperature sensor signal.I proved this by disconnecting the wires on the working scope and....... the working scope showed the same failure. Further investigation showed the black and blue wires to connect to pins 8(0V) and 7(Sensor) on the InSb detector interface, so no other electronics involved at that end.Checking the voltage across the temperature sensor test points 4 & 5 with the cable disconnected gave a measurement of 4.093V. I reconnected the cable and checked the voltage across test points again after a cold start. The voltage started at 0.715V and rose to 0.780 V after a minute so this was indeed a diode sensor connected to the input of the cooler controller PCB.Checks on the faulty scope confirmed that the blue and black wires had continuity to the pins on the InSb detector interface but there was no diode junction between the pins. The temperature sensor diode is open circuitThere is no fixing that diode so if there is not a "spare" on the detector that is brought out to its detector interface pins, it is game over for this scope. I can spoof the input to the cooler controller input to make the cooler run at full speed and cool the detector, but there would be no cold finger/detector die temperature management present.For reference, the temperature sensor diode feeds an op-amp type LMC6061 and there is a voltage reference type ADR291 that may also be associated with the circuit.Fraser

author: lowimpedance
author_rank: Super Contributor
timestamp: June 29, 2025, 02:00:46 pm
content: Thanks Fraser for the in depth evaluation, allowing us 'civies' to have a peek at this fascinating kit.Shame about the open cct diode. Are they that delicate?

author: Fraser
author_rank: Super Contributor
timestamp: June 29, 2025, 02:33:51 pm
content: Low impedance,No worries. I was taking them apart for repair so no asleep to photograph the internals.Regarding the cryogenic temperatures diode temperature sensor, I honestly do not know how fragile they are as I have never worked with them. I was a bit nervous of applying the stimulation voltage from my Fluke 87 MK iii as that can illuminate an LED and I am not sure if the PN junction of the cryogenic diode is susceptible to voltage damage as they are not a standard diode. Some specialist components can be tested with common general use test equipment but can have their characteristics changed by the test voltage and current so I wanted to be careful. I still do not know whether any special care is needed when testing these cryogenic diodes but the stimulation voltage in the thermal scope is over 4V so they cannot be that fragile.As to why the diode failed in one of the thermal scopes, I have no idea at the moment. Just bad luck maybe or potentially someone opened the scope and killed the diode during testing ? They are static sensitive.Interestingly, during testing of these scopes I found failed Vishay “Tantamount” Tantalum capacitors on the power supply DC input (3.6V) and I witnessed both tantalum input capacitors failing on the scope that has the O/C diode during my testing on an external lab power supply. They were glowing on my THOR-002 thermal cameras display so, whilst not shorted, they were in the process of dying, and drawing excess current.

author: olivir
author_rank: Newbie
timestamp: June 29, 2025, 04:08:02 pm
content: It was pretty common to put a spare temperature sensing diode on the FPA in these dewars. I see a few spare pins on the dewar, I wonder if you may find one there. The diode was typically the emitter-base junction of a 2N2222 transistor or some times a 1N914 diode. I'm not sure why yours is open, check to see that the 4.093 volts is current limited to less than 1ma. You may have a bad wire bond, who knows? These diodes were always kept physically separate from the readout to prevent cryocooler controller noise from getting into the signal path. Good luck Fraser I hope you get it working!

author: Fraser
author_rank: Super Contributor
timestamp: June 29, 2025, 04:50:33 pm
content: OlivirThank you for this “ray of hope”. I thought I had read of two temperature sensors being present on many FPA’s but I think that related to BST and microbolometer technology so I was not sure about cooled detectors. I shall check the current limiting on the diode input and search for the ‘spare’ diode junction, if such is present on this particular detector assembly.Thanks again, I was about to consider the scope beyond repair but I will check again before doing soI am pleasantly surprised that the diode junction could actually be something pretty generic in nature. I will tread carefully when looking for the possible ‘spare’ junction though.Fraser

author: MrSheep
author_rank: Frequent Contributor
timestamp: June 29, 2025, 08:31:02 pm
content: I could check my 256x256 Milcam if there is a spare temp sensor, when I get the chance. Most of the time these FPA's have two temperature sensors. One for the cryocooler. One for the mainboard. Many FLIR cameras use both so u can see the FPA temp in software, Like your SC6000.Also as scary as it sounds. I have used my FLUKE 87V and my Keysight bench meter to test the temp diodes of the FPA. So you should be ok to test with yours. The reason I believed it was ok was because it used a common 2N2222 as the "temp sensor". I was confused at first because didn't think a transistor was a diode but it makes sense when it is a p-n junctionAttached is a photo of an FPA and it's temp sensor (very tiny square towards the top) This is out of one of my LN2 Dewar cameras.

author: Fraser
author_rank: Super Contributor
timestamp: June 29, 2025, 11:11:48 pm
content: MrSheep,Thank you for the information. I am considering removing the Stirling Cooler assembly to gain better access to the detector PCB and pins. I do not know the common pinouts of a cooled detector FPA but suspect it will need similar signals and biases to a microbolometer.I need to determine likely candidates as a second diode connection. I also need to do more testing of the cooler controller PCB in case it has a problem that destroyed the diode that was connected to it.Regarding the use of the PN junction of a transistor, I remember reading that a transistor junction is a better choice than a common PN diode junction. I forget what the reason for this was. I was looking into diode temperature sensors when I bought the cryogenic thermometer that uses such a junction as its input.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: June 29, 2025, 11:18:29 pm
content: I just read a design note on using diodes and BJT junctions as temperature sensors. The Transistors junction thermal response is superior to that of a diode, making a BJT connected as a diode the preferred choice.https://www.analog.com/media/en/technical-documentation/application-notes/an137f.pdfFraser

author: MrSheep
author_rank: Frequent Contributor
timestamp: August 03, 2025, 03:42:07 pm
content: I was reading up on some ROIC data sheets last night. I noticed that FLIR (at least their old ROICs had 1 temp sensor pad on the ROIC). Not sure if they had another temp sensor. On other ROIC Datasheets (different company) that I have, they use two temp sensors. I am not sure if FLIR made 256x256 sensors. I know Amber did as well as Santa Barbra Focal Plane did, so they may be using their sensors.Hopefully your camera does have an extra temp sensor. Otherwise it might be a parts camera. Would you consider tearing that one down for science? Although it would hurt me to see you take apart a working cryocooler.One experiment you can do is jumper the black and blue wires leading to the cryocooler to see if you get an image after removing the jumper at 7-10ish minutes.

author: Fraser
author_rank: Super Contributor
timestamp: August 03, 2025, 04:07:38 pm
content: Hi MrSheep,Thank you for the information. I could not find connection information on the Coolers and FPA’s when I searched. May I ask which document contained this connection information please ?Sadly I have not been able to locate a second temperature sensor junction.I did place a 1N4001 diode across the black and blue wires and the cooler spun up to full speed followed by smoke coming out of the PCB, location yet to be found. I am thinking that the constant current power feed to the diode temperature sensor failed and fried the original FPA diode temperature sensing junction. It tried to do the same to the 1N4001 rectifier diode and the diode wonI have not had the opportunity to dig further into the issue. I am still minded to attempt running the cooler on a timer and having it drop to the slower temperature maintenance mode after the timer expires. It would be completely free of control but may still work as this is not a measurement device and I have not heard the collets in my other camera change motor speed once the operating temperature is achieved.As to tearing down an otherwise functional cryo cooler, that would be a real shame as the FPA dewar can be removed and the cooler repurposed. I already dismantled that SC3000 cooler and do not expect much difference within this scopes cooler.Fraser

author: MrSheep
author_rank: Frequent Contributor
timestamp: August 03, 2025, 04:19:28 pm
content: Oh wow. ok that is interesting. There may indeed be a fault in the constant current circuit that fed the diode. Maybe this is the cause for the FPA diode going faulty as well.You can try implementing a new diode and gluing it to the cold finger but those cryogenic sensors are expensive and since you do not have the high vacuum equipment to pump it back down it wouldn't be possible either.https://www.dwyeromega.com/en-us/cryogenic-silicon-diode-temperature-sensor/p/CY670?srsltid=AfmBOorJ67XTerMAqCN33Le-GPTx-hsC60UQqGOudZxBpcdfNmqf5jkRI actually need to buy one of these in the future to convert my LN2 dewar into a Stirling Dewar.I was waiting for someone to teardown a MC3, but guess I may bite the bullet. I have two cameras with cryocoolers in need of service that use the FLIR MC3. A Milcam and an Inframetrics PM290. I have to choose 1 to sacrifice haha. Leaning toward the PM290 as I have more than 1.I need "Test Subjects" as I am still designing my Custom Fill/Purge system.

author: Fraser
author_rank: Super Contributor
timestamp: August 03, 2025, 04:28:38 pm
content: Hmmm,From what I have read, my Cryothermometer can use a simple inexpensive BJT junction as its sensor. Yes for precision it details some specialist junctions, but only for very high precision applications as found in some science experiments at cryogenic temperatures. Unless great precision is needed for the cold finger temperature, it might be possible to use a BJT. A few Cents vs hundreds of Dollars that may not be necessary. My cooled cameras are calibrated to read temperature from incoming radiance so cold finger temperature may just need to be set at around 77K on the cooler controller and then a normal calibration of Radiance to Temperature with a black body and the cameras calibration routine.Fraser

author: MrSheep
author_rank: Frequent Contributor
timestamp: August 03, 2025, 04:34:26 pm
content: If I do decide to teardown my PM290. I will probably try to open the dewar as well. The information gained might be worth more than the cost of my original purchase.We will 100% know then if there are one or two diodesAlso it will push my capabilities to the limit. The ultimate test of if I can solder back dewar, pump down, and pinch off copper tube. And then purge/fill the MC3 Cryocooler.

author: Fraser
author_rank: Super Contributor
timestamp: August 03, 2025, 04:39:19 pm
content: Lake Shore, who make my cryo-thermometer, have a datasheet on their cryogenic diodes that may be of interest. They consider their more economic DT-471 a good choice for those not needing to go down to 10 Kelvin !https://www.lakeshore.com/docs/default-source/temperature-catalog/lstc_dt400_l.pdf?sfvrsn=de4b4a65_2&srsltid=AfmBOopPy7elJEI2Q-iw-SY8-oOZkIZHYPWYy6gY6BYfelzgBo7CrdaaI will capture some pages out of the user manual for you.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: August 03, 2025, 04:46:44 pm
content: I just found the digital copy of my Lake Shore thermometer manual……https://www.lakeshore.com/docs/default-source/product-downloads/201-208_manual.pdf?sfvrsn=3e005946_1&srsltid=AfmBOoqGmqjbKNPsOEhQr_o1SsfPG1S8xXRD-j-ktIWnbUthLTxHQh3CIt details the different diodes and characteristics

author: MrSheep
author_rank: Frequent Contributor
timestamp: August 03, 2025, 04:51:05 pm
content: Wow great find. And yeah I agree we don't need to be super precise. And yes the DT-471 sounds like a great choice

author: MrSheep
author_rank: Frequent Contributor
timestamp: August 05, 2025, 10:48:29 pm
content: @FraserAttached are pics from my 256x256 detector from my Milcam. I don't know if it will be helpful but here they are.The connector with the blue sharpie mark on it is the Temp Diode (J4).The proximity electronics PCB shows 24 pin. It seems like most MC-3 IDCAs have 24 pins. Even the 320x256 arrays. I have to check my 640x512 arrays but it is possible they are the same number of pins coming out of the dewar.

author: Fraser
author_rank: Super Contributor
timestamp: August 05, 2025, 11:09:46 pm
content: @MrSheep,Many thanks for these very interesting pictures of the MILCAM MC-3 assembly. I will be removing the MC-3 out of the MIRV and shall compare it to your pictures.Fraser

author: samuel_hayden
author_rank: Contributor
timestamp: August 06, 2025, 05:19:07 am
content: Quote from: MrSheep on August 05, 2025, 10:48:29 pmInteresting, mine looks different than yours...I'll have to pull it out again and look at it better for comparison.

author: MrSheep
author_rank: Frequent Contributor
timestamp: August 06, 2025, 05:34:37 am
content: Yeah yours might be slightly older. On the boards mine are from 2001.I had to take lots of picture and do a few sharpie markings since it is really a mess in there haha.

author: samuel_hayden
author_rank: Contributor
timestamp: August 06, 2025, 05:51:00 am
content: I believe dom is 98 or 99...I'll have to look again at the markings. Mine still works, looked BNIB....still had the FLIR warranty sticker.The IDCA design didn't change much anyway, I actually should compare it to the IDCAs on my u7500 and 8500....since they're all MC-3s and those are 384x256s..worth a look and I don't think I have pictures of the idca boards on those.

author: MrSheep
author_rank: Frequent Contributor
timestamp: August 06, 2025, 05:58:17 am
content: Yeah unfortunately mine isn't working. Not to worry though that might change in the future. The sound of the cooler seems fine. (No bearing rattle) It is a very smooth pitch and sounds similar to my working coolers. Probably just a decrease in helium pressure over time. It is over 24 years old haha.And yeah I noticed that as well. I've seen modern MC-3s and besides some parts painted black. They all look the same on the exterior. I'm curious if they made improvements in the interior. But I doubt anyone would want to open a perfectly working cooler.

author: samuel_hayden
author_rank: Contributor
timestamp: August 06, 2025, 06:06:48 am
content: Be sure to post if you manage to cook up the recharge setup. Luckily only one of the cores we've bought has had a dead cooler and it was a ricor rotary model on an L3 unit, might be interesting to disassemble itAlso have a mid-80s martin marietta cooler (used with a scanning array) that's dead-ish that might be interesting to take apart....

author: MrSheep
author_rank: Frequent Contributor
timestamp: August 06, 2025, 02:54:12 pm
content: Fraser already has a teardown of a Ricor (Style) Cooler.The L3 Units usually had a K508 so this is similar if not identical internally:https://www.eevblog.com/forum/thermal-imaging/micro-stirling-mechanical-cryo-cooler-teardown-by-fraser/I prefer the K508 cooler much better than the MC-3s as they are more compatible and easily obtainable. They are direct swap to the Thales RM3 as well.

author: samuel_hayden
author_rank: Contributor
timestamp: August 06, 2025, 03:33:22 pm
content: Yeah I was more interested in seeing the failure mode for that particular unit with how it sounds, obviously probably a couple easy guesses but worth looking for fun eh?The other L3 units have L3 B610s or D2s iirc

author: MrSheep
author_rank: Frequent Contributor
timestamp: August 06, 2025, 03:40:24 pm
content: Oh yeah if it sounds loud it might be the bearings. Feel free to make another post about it.

author: ArsenioDev
author_rank: Frequent Contributor
timestamp: August 06, 2025, 06:09:44 pm
content: Not that its loud, rather buzzes and gets quite hot.Pretty sure it's seized.

author: MrSheep
author_rank: Frequent Contributor
timestamp: August 06, 2025, 06:20:59 pm
content: Oh wow if it buzzes and sounds seized then you have to see if it is the stator/coil or the actual displacer/piston inside. You won't know until you can take out the unit and put it on a bench.I had an incident where there was no movement in the cooler and no current draw whatsoever to my RM3. Thankfully it was just the stator. After replacing the stator I was able to use the camera normally.