S2/SHS Problem

[danderer]

I have an S2 computer with external SHS (so effectively an S2G) that has worked satisfactorily for several years. It has now developed several problems. These are not consistent but happen periodically (between minutes and hours). Symptoms:

- Sitting tied to the dock, the heading data rotates clockwise in 360 degree circles at a rate of perhaps 15 degrees/second.

- When at the dock or underway, entering AUTO mode causes the rudder to immediately go significantly (in some case hard) left. When this happens the heading data is still correct—that is, it matches that when AUTO was engaged. The heading data is NOT rotating at this point.

The problems are independent. I haven’t observed both at the same time.

Powering the computer off and on solves these problems sometimes.

More interestingly, disconnecting the SHS seems to solve the problems permanently. I’ve never observed the problems with the SHS disconnected.

The SHS bench tests correctly (proper voltage and expected changes when rotated). I’ve also swapped in a different, good SHS and the problems persist.

What is the recommended path forward here?