SC-33 abruptly swinging heading

[lucas111]

Hi,

We're experiencing strange behaviour from SC-33 regarding its heading readings.
It was working with no issues 3 months now, however last night during crossing, the heading started changing abruptly.
By abruptly, I mean we were on 240degrees constant, the heading went to 10deg, swinging towards 100, just to change to 300deg swinging towards 260degrees, etc.
Pitch got stuck at 20deg, roll at 15 and not moving.

Today I've run diagnostics and all list shows OK, except Sum IMU group, that doesn't show OK, nor Fail, just "-".

After restarting the equipnet the strange out-of-control heading behaviour did not stop.
Statistically, 80% of time is stays with 240degrees (as our compass heading), just to start swinging 360desgrees 20% of time. Of course that makes it not much of a use for navigation purposes.

Anybody found similar problems in the past? If such, I'd very appreciate an input how to solve that issue.

I will try to upload video of FI-70 showing the behaviour soon.
BTW, yes, it is fixed firmly on the mast.

KR,
Lucas

 

[lucas111]

Since cannot upload MP4 file, see attached wetransfer link:
https://wetransfer.com/downloads/657923 ... 057/7b350a


Lucas

 

[Johnny Electron]

Do you have any photos of the boat showing the SC33 where it is mounted and the items surrounding it?

 

[lucas111]

SC-33 is mounted on 45m mast withL
- an IP camera underneath, which should not matter
- Sailor 4300 around 1m apart which operates on frequencies 1616-1626MHz.
https://www.theastgroup.com/media/share ... nstall.pdf

I've checed the frequency overlap and as per manuals there's clear spacing.

Apart of it, both systems were working perfectly for quite a while.
Shouldn't IMU test on Diagnostic page be OK or at least give any feedback?

 

[Johnny Electron]

The sub IMU board is a very uncommon accessory board that isn't installed and it is normal to show "- -" when not installed. I suspect by your video you are getting some issue due to the installation location on the boat.

 

[lucas111]

It's been quite some time we've replaced the unit with another one that is working corrently.
When plugging the error-giving unit into the system and passing through diagnostics I see the following (as on the pictures).
Now it only gives us airpressure and temperature.
Any suggestions how should we proceed?

 

[lucas111]

and an extra screenshot.

 

[Johnny Electron]

I would guess the location on the boat to other items is blowing out the front end amp of the antennas over time. It isn't all about frequency it is also about power. When a unit is picking up very small signals from the atmosphere, you don't want to mount anything near it that will be screaming in its ear. This is what I expect is happening. Replacing it at the same location without any other changes will most likely result in the same happening again.