If this is just a simple motor, pulley and belt drive, look for the pulley
slipping on the motor shaft. They used a press fit on early motors, no set
screw or key. I have had no luck with peening the shaft or using a thread
tightner glue (Locktite). Also it is very easy to damage the motor trying
to fix the problem. Raymarine's solution...buy another motor with attached
pulley and swap it out.
Doug K7ABX
"jps" wrote in message
...
In article ,
says...
I've got a unit that is about 7 years old.
Recently, it started turning erratically, causing the display to
pop the Antenna not rotating message, and shutting off.

The antenna's turning, but slows about every 1 to 1.5 revolutions.

I've changed the belt, and had a good look at the unit. It appears
clean, and uncorroded.
I'd like to suspect the stepper motor, as that would be a pretty cheap
fix, but before I go there, I'd like to hear some opinions of what
else might
be causing the stepper to speed up and slow down like that.

TIA

I would highly recommend calling Raymarine and talking about this with
one of their techs.

A couple of years ago I had a bad mosfet chip on my scanner pcb and they
helped me diagnose it, isolate it and point me in the right direction
for a $4 part that fixed it.

If you get someone whose not so helpful, call back another time and try
again.

jps