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. This issue had plagued this Raymarine radome from the time it was manufactured.



I removed the pulley with a small gear puller. It's a press fit, held only by friction.



The magnetic rotor is visible on the left.



There is little clearance between magnetic rotor and fingers. Any runout (wobble) that is sufficient for the rotor to rub the fingers may bind the rotor if it stops in a wrong position. Once bound the motor wasn't able to overcome the friction and get restarted. I removed the rotor and turned down the magnet in a lathe very *very* carefully until it ran true. Very little material had to be removed to make it run free of the fingers.



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



This shows the motor installed in the scanner.