(FIXED) Help with Agema 870 with 800V control unit - Page 1
Forum section: electronics / general

author: richnormand
author_rank: Unknown
timestamp: May 11, 2020, 09:15:13 pm
content: Got this IR Agema unit with what looks like a decent lens. (Model 870 and 800V control box)Scanner head seems to work OK and does output scans at about 25 Hz rate as well as 400us lines (2500 Hz).As you can see from the photo the TV video output (NTSC) is well synced for all the number info but the IR video is continuously rolling. Something is wrong with the scan conversion.Visit to FLIR for schematics and pinouts were not useful. I have the original Agema user manuals and software.I located the 4046 phase lock loop and it does seem to lock properly to the scanner. This is done via a 74112 dual J-K flip-flop in the loop to perform timing delay and division before going to the VCO and putting the data in the memory (somewhere) to be processed and read at the TV rate.This is where to sync to read the info seems to go bad. There are so many signals on the memory/read board that it is hard work to keep up without a schematic or even a block diagram. Since to boards have to be plugged in most of the assembly is not readily available for probing while the unit is working.The other worry is the multitude of UV erasable EPROM of the 27XXX series that tend to "forget" with age. If that is the case, it is probably impossible to get the original code!I am beginning to think I might be better off to take the scanner head signals and do the rest with modern electronics and micro.... and even then my SeekThermal might be better.It is a very well built instrument and I would hate to see it go to the scrap heap.(MODS: feel free to move to "Repairs" if that is more appropriate. I posted here instead of the repair forum assuming the higher probability of someone being familiar with this tech here.

author: richnormand
author_rank: Unknown
timestamp: May 16, 2020, 12:28:21 am
content: Found open cap in PLL output to mem board. Explains the lack of horz sync.Found bad ground on scanner module board (not the scanner head). The solder crimp to board was open inside the heat shrink sleeve. Found by getting anal-retentive and measuring all i/o cables.The output from the scanning head was present but it seemed that the vertical sync signal was not getting to the PLL board (only the horz one).The fun fixing stuff without a schematicBeing made in Sweden I am sure there was very good schematics. Shame they were never made available after when the camera became not commercially relevant.REPAIR, REUSE, RECYCLE, REPURPOSE....

author: Fraser
author_rank: Super Contributor
timestamp: May 16, 2020, 08:35:53 am
content: Well doneI asked FLIR about schematics etc for these old cameras and they are still protected under original corporate confidentiality. They also suggested that release would be an issue due to the technologies use in military systems.As a side note, I just repaired an AGEMA THV450 that is basically the 870 scanner head and controller combined in one, shoulder mounted, unit. The scanner head is in fact the same, just grafted into the THV450/470 chassis. Your unit is of similar age so please be aware that the glue used in the multi faceted scan mirror drive coupling has degraded with age and can fail without warning. In the case of the 450 the glue had turned to powder and let go during an initial test of the servo system.I should upload the teardown of a THV470 that I did before working on the 450 as that may be of interest. The THV470 camera had exactly the same adhesive degradation issue. The mirror drive foam coupling was left held in position via friction alone and fell out when the drive assembly was dismantled.The multi-faceted scan mirror is driven by a very high quality motor via a flexible shaft coupling comprising two aluminium shaft rings with a foam ‘donut’ glued between them. The motor is attached to the cameras chassis via a foam Vibration isolated mount that also suffers adhesive degradation. In both cases the old adhesive is removed with a scraper and fine abrasive paper (wet & dry 1100).The coupling and motor mount is then rebuilt using Evostick impact adhesive that is left to cure for 2 days. The motor coupling has to be axially aligned to prevent misalignment of the two shafts and resultant vibration and lateral forces etc. I made a mandrel for the task but be warned, the two shafts are different diameters ! Once repaired the coupling and mount should be good for another few decades. Be warned, removing the Multi faceted mirror and its motor drive is not a 5 minute job as great care is needed and you must not touch the polished aluminium mirror faces ! It’s a job that required time, patience and planning to maintain mirror alignment so lots of accurate scriber marking of the mirror mount, motor position and its mount alignment in the chassis. There is also a mirror position optical sensor that must be carefully aligned so must be marked up before removal. The whole task is quite the mechanical alignment challenge! I spent many hours working on the THV450 but I would not rush to do the mechanical restoration again in a hurry.Fraser

author: richnormand
author_rank: Unknown
timestamp: May 16, 2020, 02:43:41 pm
content: This is an interesting comment about the glue Fraser.Was the mirror damaged when it became free? I now wonder if I should do a preemptive intervention or just wait until I have to go back in there...Took the morning to reassemble everything and it is now doing a burn-in just to make sure all is OK.

author: Fraser
author_rank: Super Contributor
timestamp: May 16, 2020, 07:33:58 pm
content: No damage to the faceted mirror wheel as it is supported by its own dedicated ball bearing race and mount.A picture speaks a thousand words so I will provide some here to explain the design.Fraser

author: richnormand
author_rank: Unknown
timestamp: May 16, 2020, 08:30:44 pm
content: Great.Saved in my Agema folder for reference next time I go in there.Cheers and thanks.

author: Fraser
author_rank: Super Contributor
timestamp: May 16, 2020, 08:40:04 pm
content: I will upload the complete teardown of the THV470 that I did in a day or two. I think you will find it interesting.I stripped the unit to a bare chassis as it is a parts donor due to corroded mirrors. The Peltier cooled thermal detector module is an interesting little beast. At first glance it looks like a thermionic acorn valve as it has connections in a ring around its mid point.Enjoy your cameraFraser