Catalina 30 TRBS #2889 "Northern Light"

Scanner motor repair in Raymarine SL70C Plus Chartplotter

The rest of the modifications.


The Thomson/Airpax S57L048S12-M4 scanner motor in the 19" radome for the Raymarine SL70C Plus Chartplotter is really not one of their better quality stepper motors. It has only a single bushing unlike other Thompson stepper motors that have a ball bearing at each end. Also, my unit from the beginning had some runout (wobble) in the magnetic rotor. Occasionally an iron filing inside the motor would get caught between the rotor and one of the 48 "fingers" and jam the motor.



I removed the pulley with a small gear puller. It was only on by friction.



Inside the magnetic rotor is visible.



There is little clearance between rotor and fingers to begin with, and any runout will ten to create friction that the running motor usually overcomes, but if it stops in a wrong position it can't overcome the friction and restart. I remove the rotor and turned down the magnet very *very* carefully until it ran true. Very little material had to be removed.



Since the pulley tended to slip when reinstalled on the shaft I ground a flat on the shaft and drilled and tapped for a 4-40 set screw.



This shows the motor installed in the scanner.