In a message dated 96-09-05 07:36:13 EDT, you write:
<< The symptom described below happens when the indicator potentiometer
in the rotor opens or when the wires from the control box to the
rotor open. This is in my opinion, a serious design flaw in this
rotor. I do not know of a work around. >>
Fret not, help is at hand......
I had the same problems a year ago... I spent considerable time analyzing the
schematic and experimenting with the controller.... The directional pot in
the motor is a ten turn unit... I (and others) NOW feel that the basic flaw
is mechanical, in that the shaft runs out of lubricant and partially binds...
This back pressure on the 10:1 gear train causes the gearing to lift the
shaft/wiper up off of the winding.... The instant the wiper breaks contact
with the winding the unit does exactly what you describe - stop rotating and
the direction indicator follows the preset knob in real time...
The proven fix is to disassemble the motor box on the workbench until you
can get the nozzle of a spray bomb near the pot and spray some teflon or
silicone lubricant up the shaft.... This has permanently cured all of the
units which have been treated this way... One should also do this on a new
unit before putting it up the tower...
Now, to the more immediate problem... What to do for now?.... I have found
by experiment that if you rotate the pot back and forth across the sticking
point in the rotation that the pot will behave itself for days, or weeks,
before the next episode... Of course, the rotor refuses to turn, so the
method I have evolved is to unhook the wires on the back of the unit and
connect a 270 ohm resistor across leads 4 & 5 , and another across leads 5 &
6 ... This will tell the control box that the beam is pointed due north...
(any values close to 270 will work) Now turning the preset knob full
clockwise and pushing the start button will allow the unit to rotate... BE
CAREFUL... or you will over run the end points and tear coax off, etc.....
only allow it to rotate a few degrees, then turn the power off to the box,
turn the knob full counter clockwise, turn the power on and press the start
button... again, only allow a short rotation and turn it off...what this does
is to jog the beam back and forth 20 or 30 degrees, mechanically wiggling the
potentiometer shaft, allowing it to pop loose and drop back down into contact
with the winding.... put the wires back on and you should be back in
business... It has worked every time for me... YMMV....
I am also reposting an earlier message on this subject, which varies slightly
and goes into obsessive, compulsive detail, but ends up at the same point....
See Part 2...
Cheers ... Denny - The "I got the Tics" rotor man....
|