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 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 preheating problem. I hope this information to be usefull for some, because we cannot find this course processor even in second hand.

https://wavesails.eu/images/Nexus%20R-1600%20Repair.png