[TowerTalk] Yaesu Rotor Problem

[Chuck Lewis]

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 at aol.com>
To: <towertalk at 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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