Steve,
I'd start by measuring the resistance of the internal rotor potentiometer at
the ground end of the cable. The pot is (at least in my G-800SDX) 500 ohms,
measured across pins 1 and 3. The wiper resistance (measured across pins 2
and 3) should vary linearly from around 500 ohms to nearly zero as the rotor
is turned through its full 450 degrees. Any departure from this could be
either a bad pot or a leakage path in the cable or connector. At the very
least, it helps isolate the problem to either the rotor/cable or the control
box.
My experience was with a leakage path within the backshell of the cable
connector at the top. The rubber boot that Yaesu supplied failed to keep out
moisture and insects; and when I had symptoms similar to yours, I found
wildly erratic readings for the resistance when measured at the ground, and
when I climbed the tower I found the connector full of insect parts and
associated goop. High humidity or rain would enhance a leak/short across
the connector pins (were talking about INSIDE the connector...where you
originally soldered the cable) and that would cause the indicator to
sometimes swing wildly, and sometimes just be "way off". I cleaned the
connector and made sure the pins and wires were free from wings, legs,
spidersilk etc. I then filled the empty space with vaseline and taped the
whole thing thoroughly (yeah, you won't find it on the "approved" list, but
it's been there for 4 years now...). I haven't had a problem since. Sure
beats removing the rotor!
Conversely, you could find a 500 ohm linear pot and connect it to pins 1, 2
and 3 on the rear of the control box (1 and 3 across the pot, and 2 to the
wiper). The "full scale adjustment" pot should now work as expected, and
turning the pot slowly should cause the pointer to sweep smoothly through
its range.
Give that a shot before doing anything more drastic!
Chuck, N4NM
----- Original Message -----
From: <W5KI@aol.com>
To: <towertalk@contesting.com>
Sent: Tuesday, March 13, 2007 12:30 PM
Subject: [TowerTalk] Yaesu Rotor Problem
>I know this subject comes up regularly, but maybe my exact symptoms will
> ring a bell for a good startpoint in troubleshooting my G-800SA problem.
> It has
> about 200 feet of cable between the controller and rotor. When put up
> new,
> it set up fine and the "full scale adjustment" was perfect throughout
> full
> rotation. Six months later, just by chance, I noticed that it was way
> off only
> at some headings. Everything is fine mechanically--no slipping, no
> binding,
> smooth rotation. But, in recalibrating the "full scale adjustment", I
> found
> that with full CCW on the adjustment pot, I was still 10 degrees short of
> lining up at the desired 180deg point in the process--ran out of pot
> adjustment.
>
> Starting at full left on the rotor, ROTATING to full right, the following
> are the readings:
> Cntlr Actual Hdg Diff
> 180 180 0 (full left)
> 270 265 -5
> 360 340 -20
> 030 360 -20
> 120 120 0
> 170 180 +10
> 210 245 +35
> 225 270 +45 (full 450deg rotation to right)
>
> I am guessing I took a power spike/lightning surge on this hilltop QTH.
> I
> just finished tearing down and fixing an internal mechanical problem on a
> G-450XL rotor, so I am comfortable tearing into this unit. MY QUESTION:
> Anyone
> know the "likely" problem with readings such as above?. Should I start
> with
> the control unit, or the rotor itself, or something else?
>
> Thanks, Steve, W5KI
>
>
>
>
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