[amsat-bb] Re: Kenpro elevation rotor repair, Sebastian - W4AS

John Kopala jkopala at gmail.com
Sat Sep 27 11:11:08 PDT 2008


The motors in these rotors use a RUN Capacitor which provides a phase shift 
to one set of the motor windings and produce a rotating magnetic field. 
When the run capacitor goes bad, you get the symptoms that your are 
describing.  Then the motor hums but doesn't run in either direction.  With 
the G-5400B, the azimuth cap is in the controller and the elevation cap is 
in the rotor.  In any case, check the circuit for the nominal 24V AC between 
terminals 6 and 4 and then between 6 and 5 with either Down or Up selected. 
If there is voltage present on both terminals 4 and 5 referenced to terminal 
6, then at least the cap is NOT open.  But it may still be shorted.  Check 
the resistance of the rotor between terminals 4 and 5.  It should read about 
5 ohms if the cap is not shorted.  You will have to open the rotor to get at 
the cap to do further testing or to replace it.

An extra side note.  Yaesu has moved caps from the controllers to the 
rotors.  So the G-400, G-500, G-5400B, G-5600B, and G-5500 rotors and 
control boxes are not interchangeable.  With the G-5500 and G-5600B, both 
caps are in rotors.  With the G5400B only the elevation rotor has the run 
cap in it.  With other models, the caps are in the controllers.

Good luck,


> From: Sebastian <w4as at bellsouth.net>
> Subject: [amsat-bb]  Kenpro elevation rotor repair
> Well I had been back on the birds for the last 3 months or so, and
> while I was getting ready for an AO-16 pass a few days ago, my
> elevation rotor on my Yaesu G-5400B stopped at about 10 degrees.
> That's it.  It won't go back down or up.
> So I checked the wiring on the rotor, everything appeared fine.  I
> removed the elevation rotor from the azimuthal, and took it inside.  I
> made a small patch cord to go from the control box to the rotor, but
> no luck.  All I get is the display of the elevation of about 10
> degrees, and I hear a little hum when I attempt to move it up or
> down.  This tells me that the potentiometer is probably good, and the
> motor is receiving power.
> I've removed the small nameplate on the side, and there is no water
> inside, and I can see the ball bears; there doesn't appear to be any
> rust inside.  I also removed the terminal assembly in case one of the
> wire had come loose, or had a cold solder joint, but I didn't find any
> problems there.  Looking at the diagram of the rotor, there appears to
> only be a small 24 volt motor which turns this; along with numerous
> mechanical parts.
> So the question is.  Before I send this to Yaesu, has anyone had this
> problem before, is it a minor one (something that I could fix myself),
> or is best left to Yaesu?  Before anyone mentions, Norm's no longer
> services these rotors.  The four 'screws' that hold the two parts are
> impossible for me to loosen.  I would have to use a vice, but I do
> have a friend with a motorcycle repair business who I'm sure could
> open it for me in 60 seconds.  To me, this looks like a jigsaw puzzle
> by looking at the diagram.
> The rotor was in service for about a couple of years back in the early
> 90s.  It then sat inside without any use, up until a few months ago.
> If the consensus is to send it to Yaesu, should I bother to send in
> the azimuthal rotor, or should I follow the "don't fix it if it aint
> broken" rule?

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