Avionics: inside a compass unit (with pictures) - Page 1
Forum section: electronics / projects

author: wobbly
author_rank: Regular Contributor
timestamp: August 08, 2025, 01:40:59 pm
content: Scored a nice looking compass-like thing for cheap (£10!).There was a date code of 1994 painted on the side, but no other info.I have no useful information about it at all. There are no manufacturer markings of any kind. The military connector on the rear is a Thorn "PT02 22-55P" (55 pins).It looks in good condition, at least cosmetically. It does not rattle when shaken, so it might be OK.I've removed all the screws on the rear panel but it is still stuck rigidly in place. It crossed my mind that it was never intended to be a maintainable item, and once damaged it was simply scrapped.I want to open it up and tinker with it, perhaps turn it into a novelty desk toy or something.Does anyone have any experience with modules like this? How can I get this thing open without resorting to a hacksaw?Once it's open I'll share photos on here since it's probably quite interesting.

author: themadhippy
author_rank: Super Contributor
timestamp: August 08, 2025, 02:28:56 pm
content: QuoteCould be a gasket or glue still holding things together,have you tried prying then apart with something like a spudger

author: wobbly
author_rank: Regular Contributor
timestamp: August 08, 2025, 02:47:20 pm
content: Yes, although the gap is extremely narrow. No signs of movement.

author: gerbay
author_rank: Regular Contributor
timestamp: August 08, 2025, 02:53:35 pm
content: https://www.youtube.com/@lelabodemichel5162/videos

author: wobbly
author_rank: Regular Contributor
timestamp: August 08, 2025, 03:27:36 pm
content: OK, I'm in. It took a lot of faffing about with a sharpened bit of brass sheet and a little percussion. I think the outer case was a little warped (or perhaps just a very snug fit) which was causing a lot of friction. There is a gasket, which didn't help.I was right - it IS interesting...

author: wobbly
author_rank: Regular Contributor
timestamp: August 08, 2025, 03:45:56 pm
content: Pics...

author: wobbly
author_rank: Regular Contributor
timestamp: August 08, 2025, 03:55:41 pm
content: More pics...A thing of beauty and a joy forever. No signs of damage or even wear and tear on the gears. It looks brand new inside.The cable wrapping is done with some sort of stiff cloth, possibly nylon. A knot every 5mm or so, very nice.No less than 4 anti-backlash gears in a fairly complex drivetrain. The indicator needle spins freely, driven by the large synchro-torque receiver.The actual NESW disk also rotates, through a fairly high gear reduction from the small servo-motor The two small photos show the disk after it's moved.There is what looks like a toroidal transformer with several taps.The photo with the red question mark shows a mystery wire, which runs around the perimeter of the dial. It's interrupted by a solder joint every 45 degrees or so. Some sort of anti-magnetic compensation thing?I bet this thing would just work if I somehow managed to wire it up with the right stimulus. Any ideas welcome.

author: wobbly
author_rank: Regular Contributor
timestamp: August 08, 2025, 04:08:01 pm
content: Looks like this was built by Smiths of Great Britain.

author: Gyro
author_rank: Super Contributor
timestamp: August 08, 2025, 04:33:53 pm
content: Quote from: wobbly on August 08, 2025, 03:55:41 pmDial lighting related?

author: DLJ
author_rank: Contributor
timestamp: August 08, 2025, 04:39:31 pm
content: Gerbay is correct lelabodemichel5162 does have a video about one of these. Here is a direct link to the video.Your instrument is missing at least two parts, one pointer is missing and the label that tells you what you haveYes, it is a Smiths instrument. I worked for them for 20 years and recognise the style of construction.I suspect your mystery wire is for backlight.Good luck.

author: wobbly
author_rank: Regular Contributor
timestamp: August 08, 2025, 05:10:42 pm
content: @DLJ, The 55-way military connector shows signs of being salvaged from another piece of equipment - all of the pins have solder on them, but perhaps only half have wires attached.Quote from: DLJ on August 08, 2025, 04:39:31 pmOmitted at the factory or scavenged do you think? No cut wires anywhere that I saw. I wonder what this was used for if it's not fully populated.

author: MarginallyStable
author_rank: Regular Contributor
timestamp: August 09, 2025, 03:15:08 am
content: Not all radio magnetic indicators have two dials (ref:https://krepelka.com/fsweb/learningcenter/navigation/thermi.htm)