Odd RRU behavior

[gotfish]

I have a NavPilot500 series autopilot using an FAP 6111 RRU (40' twin inboard). The boat hasn't been used for a few months while I had the helm pump out getting rebuilt. I reinstalled the helm and bled the system this week (with the steering cylinder disconnected from the rudders). Upon reconnecting the steering ram cylinder to the rudders and turning the helm, the displayed max rudder angle was incorrect/uneven at P/S hardcover and wasn't following the actual rudder movement as I turned the helm. After a few cycles back and forth and verifying that the displayed angle was not consistent with the actual rudder position, the displayed angle stopped at 3 degrees stbd and doesn't change anymore. I disconnected the mechanical connection between the RRU and rudders and get no change when I rotate the 6111 arm. I power cycled the system several times but no change. And the startup self test screen says RRU 3s (matching the displayed rudder angle).

I've researched other posts on this forum and found the info on testing the RRU resistance so I'll do that next time I'm on the boat to see if I have a bad RRU. In the meantime, I'm wondering:
1) Would a bad RRU show a unchanging angle like I see that's not min or max or zero? Or is the unchanging reading of 3 degrees stbd indicative of another problem?

2) Since the 6111 is obsolete, do I need to do anything to the rest of the system to replace it with a 6112?

3) The wiring between RRU and the AP blackbox under the helm is rather circuitous. If I verify incorrect resistance readings on the cable at the blackbox (indicating a bad RRU), can I then cut the cable closer to the RRU, verify the readings are still incorrect at that cut point, and then splice in the new RRU cable at the cut point?

Thanks,
Tom

 

[FishTech]

Where the arm of the RRU connects to the base, there is a screw to tighten the built in clamp that wraps around the shaft that runs into the base. Make sure that clamp on the shaft did not come loose. There is a slot for a "flat head"/slotted screwdriver on top of the shaft, so you can watch that to see if it is moving when you spin the arm around.
The next step would be testing the resistance as you already plan to do.

 

[gotfish]

Thanks for the reply. I noticed that feature on the 6112. I have a 6111 which doesn't have that shaft clamp feature but does have a small set screw holding the arm onto the shaft. I'll check that.

 

[FishTech]

You are correct, that was my mistake. Definitely make sure the shaft is rotating.

 

[gotfish]

Bingo! Tightened the two tiny set screws that hold the lever arm to the pot shaft and readings follow the rudder again. Then just moved them to a zero rudder angle on the readout, loosened the set screws, centered the rudders, and retightened. I love it when there's a simple fix.

 

[gotfish]

Thanks for sharing your expertise!

 

[FishTech]

You're welcome. Happy to help.