AGEMA Thermovision THV470 camera complete teardown by Fraser

[Fraser]

The fixed mirror assembly. One fixed mirror is still in the chassis so not shown.

The surface corrosion is clearly visible. These should have a highly reflective mirror polished surface !

It is surprising that there is no moisture control within this camera. No Silica Gel packs, nothing. Aluminium corrodes readily in a damp atmosphere.

Fraser

[Fraser]

A selection of full resolution images of the cooled detector element for your delight and delectation 

[Fraser]

The principle of the SPRITE detector element. This and the associated pictures may help to make sense of what we can see in the pictures I took of the SPRITE detector.

Taken from a scientific paper on the SPRITE detector....

In the SPRITE an element is fabricated that is around 10 times as long as it is wide. The MCT detector material is biased with a current source. This causes the mobile carriers generated by infrared radiation to drift towards the read-out zone. If the drift speed is matched to the speed at which the scene information is being scanned across the SPRITE element, then all the carriers associated with a particular part of the scene arrive in phase at the read-out region. This improves the signal to noise ratio and greatly simplifies the use of the detector.

[Ultrapurple]

Wow Fraser - that's a shed-load of photos and I have no doubt they will be used as the 'standard reference' in the future.

I'm always amazed just how methodically you work and how rigorously you document everything as you go. I'm aware that most of the time it's just for your own reference (did the brown wire go here or there?) but I know from my own experience that even getting good quality snapshots is no mean feat.

Thank you for sharing this with the world.

[Fraser]

It was pretty much a dump of my picture archive and not what I normally like to do with pictures carefully selected for content. There is a lot of duplication so I will go through this threads pictures in slow time and delete the duplications. I provided some duplications, like the sensor as I did not have time to check which was the better focussed or lit. “Cat” wanted to see what the inside of the scanner looked like so I quickly uploaded what I thought might be useful I just hope the thread is of use and interest to someone.

Fraser

[Fraser]

As Ultrapurple has stated, I carefully record the disassembly of equipment I work on. Relying upon memory can be risky when it comes to complex equipment. Knowing the original path that flexible cables took can be invaluable and avoids potential pinching of said cables during reasssembly. Service manuals for thermal cameras, even those from the 1980’s are not generally available (with the odd exception). As such it is a good idea to document working on a particular camera for future reference and to aid re-assembly  I extreme cases, it can be worthwhile to video a complex disassembly operation so that the recording may be played in reverse to reassemble the parts exactly as they came from the factory. I do not usually need such video recordings though. My brain seems to be ‘wired’ for methodical disassembly and re-assembly.

Fraser

[gchafee]

Hello, I know this is an old thread, and I have not been on the forum for years, but I came across this and had to re-sign-up to contact. Is there any chance anyone kept this thread in a booklet type form (like a pdf) where all could be found (and downloaded) easily? I am very impressed with the information. I would love to see if there are other teardown type information on items like the military AN/PAS-13B or the AN/PAS-23? I am going to start on my own with the PAS-13B because they also have the spinning mirror system like the Agema 470. I am somewhat familiar with the basic design and would be happy to document disassembly with pictures. The motor for the spinning mirror is noisy, not unlike every Agema 470 I have owned, but much quieter. Only by a teardown will I be able to track down if they can be silenced as originally made by Raytheon. Either way I would appreciate any words of wisdom.

[Fraser]

The spinning mirror motor is almost silent in operation as it is a very high quality unit. It is the spinning mirrors ball bearing race that makes the noise and it is a sealed unit with no easy, low risk, way to rebuild that bearing with fresh lubrication. The THV scanning cameras were always a bit noisy because of the ball bearing race. The mechanical tilt drive of the other mirror is also naturally noisy in operation.

Fraser

[gchafee]

I have 3 THV450s. All of them are so noisy it is difficult to stay in the same room with them when they spin up. One unit came to me with a box of disposable earplugs as part of the accessories! Strangely enough, the noisiest unit is the only one that works correctly. I am hoping to use your teardown to see if it is possible to correct this and quiet it down. I assumed the noise is coming from the mirror motors as they sound similar to a laser printer mirror motor when they start to spin up. You have referred to the ball bearing race as being the culprit. Is the race you speak of separate from the motors? Have you run into any units that had very loud motors or bearing races?

It is unfortunate the mirror motor race is sealed and at high risk of damage to rebuild. I am not sure how to approach the issue of noise on the THV450 or the PAS-13B units. Possibly I would be lucky and find that cleaning the old race and attempting a small amount of lubrication might help. I will need to pull the motors to decide. I know the PAS-13B motor is audible withing 2-3 inches of the unit's casing. Raytheon sold them as silent to the military, so I suspect something may be wrong.

If you didn't have any other documentation on your THV470 teardown, I will use the thread to attempt it. Years ago, I used to attempt to reverse engineer other equipment I had (including drawing out schematics) to help understand and repair them. I had a CAD program just for creating schematics. If I get anywhere with the THV450s, I will share what I find if you wish. Note that this only applies if this uses 1- or 2-layer circuit boards since it is nearly impossible to trace the runs on multilayer circuit boards. I am not sure that would work on the PAS-13B as Raytheon has been known to erase any identifying characters on the ICs, or have proprietary markings on them.

I have a PAS-23 that I purchased inoperative. I remember someone at some time stating that attempting to disassemble these units will damage them where they can't be repaired. I am wondering if anyone does repairs on these units so I would not have to find out the hard way. Do you have any information on these units?

Any thoughts?

[Fraser]

The PAS-13B and PAS-23B that I am aware of were microbolometer based but your Raytheon unit sounds different. I shall have to investigate. When I think of early Raytheon systems that are ‘silent’ but make a whirring sound…. I think of the Raytheon BST based technology that uses a spinning chopper wheel. Units like the AGEMA THV 510 uses scanning mirror and ‘purr’ when operating.

The problem with the noisy rotating mirror system in the THV-450 and 470 is not uncommon as the ball bearing race suffers lubrication loss over time. It is a high spindle speed so the bearing starts to sound like someone shaking a tin of bolts ! The challenge is in getting to the ball race. The high quality motor is usually very quiet in operation. The motor spindle drives the mirror wheel shaft via a sound and vibration dampening foam ‘Donut’. This can become unstuck from its metal spindle holders and causes the camera to fail as the spinning mirror is static. The tilt mirror control loop is synchronised to the spinning mirror so failure of the motor coupling to the mirror also prevents tilt mirror operation.

The spinning mirror has a spindle that passes through a high speed ball bearing race. This ball bearing race resides in a recess at the bottom of the mirror wheel. I could see no way to remove the bearing without likely damaging the very fragile polished aluminium mirror faces. It was assemble, so it can be disassembled…. But the risk to the mirror wheel must be considered. The outer section of the ball bearing race is secured to the cameras chassis so the mirror wheel is held exactly in the correct location via its spindle that is secured in the ball race inner ting. Hope this helps.

These cameras often suffer from damage caused by a leaking Lithium Thionyl Chloride battery that supports the RTC and  settings  memory. The servo drive system that powers and synchronizes the spinning mirror and tilt mirror are also prone to component failures due to age. Failures of the Microprocessor PCB are also quite common.

Basically, the THV450 and 470, if still working, are on borrowed time due to age related degradation in the system. This is why I laugh when I see them on eBay at high prices…working units are basically a ticking ‘time bomb’ waiting to throw up a fault.

Hope this helps

Fraser

[Fraser]

The relevant pictures of the spinning mirror wheel and associated bearing system.

[Fraser]

I have found the PAS-13B of which you speak. I only know the later 2006 models. Yours is presumably the cooled version so may well be like the THV-450/470 scanning technology. If such is the case, some scanning units operate the mirrors in a vacuum and this can be an issue if you disassemble the scanning section. I regret I have no information on these military units or what resides within them.

https://web.archive.org/web/20100705003911/http://www.raytheon.com/capabilities/rtnwcm/groups/ncs/documents/content/rtn_ncs_products_tws_pdf.pdf

http://www.2ndbn5thmar.com/night/PAS-13.pdf

Fraser

[catjuice]

THANKS so much! I had a thermovision 870 scanner that just recently started giving me issues. it was having problems maintaining speed and would miss the video sync every once in a while until eventually it stopped spinning it's mirror polygon all together. it was that darn foam donut and it's adhesive that had come loose. I probably would've never figured out what exactly the issue was without this thread. I used a little adhesive to reattach the donut coupler to the motor shaft and it works good as new.

[Fraser]

catjuice,

I am pleased that my post helped you   

Fraser

[ThermoVisão]

Hi Fraser... Thank you so much for all your excellent  work on dismantleling this wonderful camera.

We have one that stills partially works and we're looking for someone that could help us.

Our camera does not open the Configuration Menu and as we have tested the rubber side press buttons are not the problem. We suspect is the firmware.

Another problem is the floppy disk that turns on but does nor read or save any file.  We tried to replace the floppy drive but it didn't work too.

Could you help us?

We'll be extremely gratefull.

Thank you very mcuh and, again, congratulations for your photos!!!

mario

[Fraser]

Mario,

Inspect the memory back-up battery that sits under the handle area of the camera. The Lithium cell fails and leaks over time. the electrolyte can travel a long way and onto the PCB's below. If there is leakage you need to fix the damage before doing any further fault finding as the conductive electrolyte can cause all manner of weird issues.

I have a complete set of PCB's and parts for the 470 camera that I will not be needing any time soon. Sadly I am deployed overseas until the end of March so cannot do much for you until I get home. The firmware is replaceable by changing out the EPROMS but I do not have a copy of those EPROMS as I had no need of the code. The PCB's I have do contain a full set of EPROMS but, from memory, the processor PCB has a fault due to battery leakage. Hence why I dismantled the camera.

Fraser

[ThermoVisão]

Thank you very much Fraser...
We are thinking about the EPROMs here...
Also... Do you have any idea on how to fix the diskette unit driver?
We've exchanged ours for another one that is working properly  but it didn't work either.
Any suggestion will help us a lot
Thanks again
mario

[Fraser]

Sat here in my overseas accommodation I am without my reference material for the 450/470 camera so can be of very little assistance to you. I cannot recall whether the FDD is a standard PC type or one that is specific to the Agema camera. It would be worth checking the original drives part number to see if Google can supply its specs for you. I have met FDD's that have custom connectors and even custom firmware and so cannot be simply replaced with a generic PC compatible version.

As to what could cause a failure in the FDD controller board... I will do a careful inspection of that PCB looking for corrosion. Where EPROM's are involved, sadly there is the possibility of age related data corruption but such is only easily found by comparing to a known good binary file.

Sorry I cannot be of more assistance to you at the moment.

Fraser

[ThermoVisão]

Thanks Fraser...
I'll check this out and let you know.
Probably will be able to open the camera in the next two weeks. You know... We have other things to do here... 
Thank you very much again
mario