Simrad Robertson Autopilot

[Tommee]

I have an old but trustworthy Robertson AP300x with hydraulic linear drive HLD2000 which has a motor RPU80. The unit is now showing rudder response failure. The unit has been unused for 3 months & when I turned it on it made a 3 sec attempt to move the wheel & stopped. Now there is no response. When I engage Auto, the wheel locks so the clutch is engaging but the wheel does not respond to command. I am guessing the problem lies in the motor. The manual suggests checking connections....these are good. Check rudder FB transm. link?? Check drive unit motor brushes. Replace junction unit Power PCB. Any advice welcome please. Is it easy to remove the motor unit? Any snags to be avoided?

[Tehani]

To find out if the problem is in the mechanical unit and the motor, disconnect the electrical connections from the pump, and manually place the rudder in the center.
Here you can do two things:
- You can power the pump directly from the battery (better through a 10A fuse). This is to check the pump motor.
- Press AUTO to engage the clutch, and power the motor directly from the battery for an instant. This is to check all the mechanics and should move the rudder.

If this is not the problem:
The course computer output circuit may have a protection fuse. If not, the problem is with that unit's power transistors, or some burnt circuit track. (Currently they are Mosfet, in their AP I do not know).

[donradcliffe]

Chances are good that it is the brushes. There have been several replacement motors for that drive, so make sure that you get brushes for the right one.

As said above, you can test the motor by jumping it directly to 12 volts. Jump the bypass valve at the same time and the drive should move.

[Tommee]

Thank you for the advice, seems it is the brushes. Hopefully a fairly simple fix

[SoonerSailor]

You can easily check the brushes on that linear drive. When new they are about 10mm long IIRC. Visual inspection should tell you their condition.