Nexus Autopilot R-1600 Course Processor Repair

[bojo_bs]

Hi Guys!

I want to share my experience repairing Nexus R-1600 Course Processor. My friends from the club called me to try to repair the autopilot. It stoped working with error code 25 "No Autopilot", rudder angle was always 0 and when SET is pressed the rudder turns right to the end. I checked rudder feedback sensor - it was OK - 1 kOhm potentiometer with 220 Ohm resistor, connected between middle pin and middle output cable. I decided to connect the NMEA-0183 to computer terminal (4800 8 N 1) and i see in the output Accelerometer Error. I changed the accelerometer chip with NXP MMA8451QR1 and then the output was OK with no errors in initalization. Fitted again on the boat and now when I press SET the autopilot follows the course, but again rudder angle was shown 0 and again error 25 when I choose HDG, AWA ot PWR ST modes. Then I decided to change RS-485 driver ADM3493, but when I see this IC datasheet there was no integrated ESD protection. I think the damage was from surge. Then I choose to try ADM3485EARZ, which has 15kV ESD protection and voila everything works perfect. The defective ADM3493 recieves input fine, but the has problem in the output to FDX network. Also I prevantive changed the Gyroscope IC L3G4200D and two LM324 op amps, because they also can be a problem. Note LM324 was Texas Instruments with integrated diodes and I changed them with the same Texas Instruments LM324DR. After that I decided to make soldering points perfect with my IR station, because I used hot air temporary. After that everything is fine, but the voltage to the ADC input to the PIC18F67K22 is from 2.7 to 3.2 V and the rudder indicator shows 2 to 32 deg. Before preheating of these ICs, which I changed was from 0.2 to 3.2 V and rudder indicator shows -45 to +45 deg. Now I will explore where is the preheating problem. I hope this information to be usefull for some, because we cannot find this course computer even in second hand.

[GordMay]

Greetings and welcome aboard the CF, bojo.
Thanks for your informative report.

[bojo_bs]

Thank you GordMay and all mariners!
Update! After 100 hours in reverse engineering and no any support from Garmin and more 20 hours on magnifier, microscope and capacitor by capacitor, resistor by resistor removing and measurement I see one small tinol hair falled from my soldering iron between two resistors. But everything shown above is true. You may decide changing only accelerometer and RS-485 driver, which is more ESD not resistive.

Now autopilot works flawesly and is more ESD protected. I hope this will help some experiencing problems with Nexus Race autopiolts. And as I see they are no small community.

Sinecerely Yours,