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[TowerTalk] Orion rotator ... trouble?

Subject: [TowerTalk] Orion rotator ... trouble?
From: Steve Jackson <>
Date: Fri, 26 Oct 2007 18:58:36 -0700 (PDT)
List-post: <>
I have the M2 Orion rotator (sorry, 'positioner') with the RC-2800P-A 
controller unit, red LED vintage.

It's sitting in the tower on a shelf near the top of 80' of 55G.  Turns an 
Optibeam 16-3, a rotating 40/30 M2 dipole, and a F12 N1217 dualband WARC yagi.

Has been there for about 7 years with no troubles until today.

I find that I can't turn the antennas counterclockwise ... I try to dial in a 
heading of, say, 160 degrees when I am at an indicated 197 degrees.  The 
display (in mode 1 at speed 1) shows that it 'wants' to go there, the relay 
clicks, but, nothing.

The other way is bad, too:  An attempt to go from 197 degrees clockwise to, 
say, 220 degrees DOES increment the reading - very slowly and erratically - and 
only by a few degrees.  Then it stops.  Can't go back CCW afterwards, either.

Attempts at control via the serial port result in the same actions.  The 
control box is not overheating, or acting oddly in any way.

DC voltage on the disconnected motor line shows about 48V DC at the box 
terminals.  The disconnected control line voltage is 11.6V at the box.  A 
resistance check of the motor leads (at the box end, and disconnected) shows 
megohms, but inexplicably with a 'negative' sign when the test leads (Fluke 
177) are reversed... odd, like it was being powered from someplace ... and 
there are about 300 mV on the motor wires.  That might be a clue.  I haven't 
the foggiest idea how one can get DC voltage off of 400' of a pair of wires 
that terminate into a motor winding!

A quick walk out to the tower, 300' back in the woods in the misty rain and at 
night, shows no obvious anomalies.  Of course, I'll do a more thorough check in 
the morning when it's light out.


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