My old Raytheon ST400 auto pilot failed me on my sail from Los Angeles to Ensenada. I was able to get a car to the West Marine store in San Diego and bring back a new system (T70153, incl, P70R head, ACU 100, a digital compass and drive arm for my tiller. 

Problem is my compass calibration repeatedly fails.

I begin the process, get a circle displayed on the screen,  and within a few seconds the head notes that the calibration is complete, deviation 188 deg., failed. 

I have tried to simply use the unit in auto mode despite not having calibrated the compass, and the drive arm immediately pushes the tiller hard to port, and after a short while the head tells me that the unit is switching off (I can then go back to stand-by mode.

Some facts:

The head gives me an accurate compass reading. Nevertheless I scanned the location and the boat with a hand bearing compass to ensure that the original location had no magnetic deviation. It was very slight, if any, but I relocated the digital compass to another area before today's failed test.

I have ensured that the cables are generally away from the engine and current sources.

This morning after the second failed commissioning, I relocated the ACU computer farther away from some wiring. I haven't tested this configuration yet, but I'm not putting too much hope in it.

I have conducted the compass calibration in dead flat water, and some gentle swell, at or under 2 knts.

I re-used the plug from my old Raytheon ST400 for the drive arm. the new and old arm and plug appear to be identical  I have a brown wire (which I wired to "A") and a blue wire (which I wired to "B") on the ACU, coming from the drive. The arm drives the tiller properly in standby mode.

I assumed that the locations of the cables to the backbone are not critical. I used the blue and black cable to connect the compass to the backbone, using a "T" connector with a white and black cable.

In the dockside wizard  I set the tiller "hard-over" time, using an average of the time it took using the head's single degree keys and the ten degree keys. I'm at 32 seconds, which appears to be slower than when the auto pilot actually pushes my tiller hard to port as per above in the not functioning auto mode.

I checked to make sure the connections at the ACU were correct. They were, and are. In fact all connection appear to be solid.

So, I'm stuck in Ensenada, wishing I could sail south. Very frustrating, but being a single hander, an auto pilot would be of great help to me.

Any bright ideas would be more than welcome.

Rob Werth,Firefly

Ps. Disturbingly, my manuals for the system do not exactly match what the P70R head menu's show me.  For example, for the compass calibration, I'm in set-up, auto pilot calibration, commissioning, re-start compass. Probably this is not a factor.

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There isn't a compass calibration for the new Evolution autopilot system, there is a cruise that will set the deviation and allow for the system to hold a good heading.  By pressing Reset Compass you are starting that process over and setting the Deviation to 188 which is a default highest deviation.  Follow the description below.

Evolution – No Seatrial Calibration


The new Evolution autopilot system does not have a specific Seatrial calibration, you are to do the Dockside Wizard, then take the boat out for a 15-20 minute cruise, doing a few circles and figure 8's to show the system all the points on the compass rose, keeping the speed between 3-15 knots.  While out on the water, press Menu>Setup>Diagnostics>About Pilot, scroll to the very bottom of the page to look at the Deviation.  If it is within 15 degrees, you are done. Restart compass is used to drop the Deviation in the system and have the heading sensor start over calibrating the Deviation, shouldn't be used unless you are relocating the EV-1 heading sensor.  Compass Lock, is to lock the heading sensor to the current Deviation in the unit, I would recommend that you lock the compass once you have the autopilot functioning the way you want it, usually after a couple of trips where you use the autopilot and it is functioning properly, because the heading sensor is always learning, trying to get a better deviation on the heading and learning the movement of the vessel for better course correction.  Once you Lock Compass it stops the learning process and holds the settings that it has for the vessel.

Thanks Underway! That may be the missing information I need to get things working. I'll try again in a few days and revert here with results


I followed your instructions. Compass deviation is now 2 deg. However, when I put the unit in Auto mode it does the same thing, pushes the arm hard over to one side or the other, spins the boat for about ten seconds and shuts down. I can then go back to Std By mode. When it does this the screen does show the heading that I intended, but the drive arm has other ideas.

Advice is appreciated



This last one was my bad. At the dock this morning I reviewed the basic settings and found that the compass was "locked". I unlocked it and the auto function now appears to be working

Your help has been much appreciated.  Perhaps you can suggest to the powers that be that the installation instructions for the P70R pilot controller, specifically section 5.7 be updated, so that the next guy doesn't have these same problems

Best regards,


Good to hear you are up and running!  I will make sure your update request for the installation instructions are relayed.  Contact us with further questions.


Auto Pilot is not working. The problem is not fixed!

I thought that it was as I did a dock test and the ilot appeared to be correcting for small changes in heading.

I left Ensenada, once again, to continue my cruise south, and again the auto pilot failed to work in auto mode. Again, I made some figure eights and checked the deviation in the diagnostics mode (3 deg now).  Tried the auto mode a few more times and it is definitely not working.

I make sure that the tiller is basically centered before I enter the auto mode.  Again, what happens is that the display shows the heading I set when I enter the auto mode. Then the drive arm pushes the tiller hard over to one side or another, and a few seconds later the system shuts down. The heading on the display does not change as the boat swings around.  I can then take it back to stand by mode.

Back at the dock I tried it again in auto mode and it does appear to be working. As the boat swings the tiller makes small changes to bring it back on the designated heading. 

At the dock: no swell, easy, minor course corrections, no forward speed, and probably some other differences vs at sea.

It seems that I've lost my weather window again. Very frustrated

Expedited help would be much apreciated




I have done some tests of the various settings. To summarize:

Limit of drive arm is ~15 deg off center. I have ensured that the drive arm is mounted so the arm is centered when half extended.

In dockside Wizard, I have tried various rudder swing limits and hard over times.

When I use 15 deg, 8 sec, the rudder swings hard to port (but drive arm motor keeps running). When I do the sbd test, the rudder only swings from port to a little past center to the sbd side, not all the way over, 15 deg past center (motor stops running)

My best setting is 10 deg, 10 sec in which case the rudder swings all the way to port and sbd, but the drive arm motor keeps running on both sides unless I continue the test to completion.

I start all of the above Wizard tests with the tiller dead center.

When in stand by mode, from tiller center position, when I swing the rudder hard over to port or sbd, the display appears to show the degrees that the rudder is moving from one side to the other. Curiously, the rudder swing is ~15 deg each side, but the display only shows ~5 deg of movement.

Deviation is currently 3 deg.

The unit appears to work in auto mode "at the dock", and in any of the settings I've tried, just as it always has done. 


So when you press Auto, while underway, the Tiller drive just goes hardover right away?  Try switching the motor wires A/B on the ACU-100. 

Thanks I'll give that a try if I can't get it working this morning


You were right. That fixed the problem.

When I installed the new P70 system, I re-used the original socket for the drive arm from the old ST4000, as its the same as the new one. It seems that the previous owner had used the blue wire for positive and...

Can you in form your cohort Mark (bad Mark) that the problem has finally been resolved?

Thanks for your help.


We're glad to learn that the problem has been resolved.




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