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Re: [TowerTalk] Yaesu Rotator Puzzle

To: "'Pete Smith'" <>, <>
Subject: Re: [TowerTalk] Yaesu Rotator Puzzle
From: "David Robbins K1TTT" <>
Date: Sat, 15 Sep 2007 12:12:43 +0000
List-post: <>
Measure the resistances on the pot and motor to ground from the shack end
with the control box disconnected.  They should both be open circuit or at
least very high resistance.  My guess would be that you have a leakage path
from the motor power to ground that it is adding a bias on the indicator
circuit.  This is based on the sdx controls where the power to the motor is
only grounded through a 10k resistor in the control box, this is what leads
to the odd one way speed differences.  So if there were a short or low
impedance leak in one of the motor power leads to ground (say one of the
filter caps in the rotor shorted), it could feed current into the ground
where one side of the indicator pot is connected. 

David Robbins K1TTT
AR-Cluster node: 145.69MHz or telnet://

> -----Original Message-----
> From: [mailto:towertalk-
>] On Behalf Of Pete Smith
> Sent: Saturday, September 15, 2007 11:42
> To:
> Subject: [TowerTalk] Yaesu Rotator Puzzle
> I have a G-1000DXA and a G-800SA for the top and bottom tribanders in my
> stack, respectively.  Recently the top rotator (the DXA) started to behave
> erratically.  When I would press the "left" or "right" ends of the control
> bar, the indicator would taker off 45-90 degrees and then begin to
> indicate
> very slow and somewhat irregular antenna rotation.  I thought I might have
> a connector problem, so I cleaned the connector at my entry panel, to no
> avail.  Then I switched the two controllers, and to my surprise, the
> problem 98 percent cleared up (the G-800 controller on the G-1000 rotator
> still displays a momentary indicator swing of ~5 degrees, before rotating
> and indicating position normally).  The G-1000 controller seems completely
> normal.
> I talked to Jerry Darby at Yaesu, who is pretty knowledgeable about the
> rotators, and he said that this was a new one for him.  He did say that
> the
> circuits of the SA and DXA controllers that senses the antenna's position
> are a little different, so that they might react differently to some sort
> of cable problem - excess capacity to ground, for example.  I'm not sure
> that I can measure that, but I did measure the resistance of the motor
> windings and the rotator pots - the pots seem virtually identical, but the
> G-1000 motor reads 15 ohms, while the G-800's reads 30.  Jerry says that
> the motors are the same, so this may be indicative, but he could not
> suggest what to look at next.
> I have a workaround, described above, but suspect that there is still
> something in the cable to the DXA that is haywire.  Does anyone have any
> suggestions for diagnostic steps I can take, hopefully from the ground?
> 73, Pete N4ZR
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