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Subject: LX200: strange RA drive behavior
From: Bill Arnett
Reply To: mapug@shore.net
Date: Fri May 24 02:46:43 1996

:-( I am NOT a happy camper!

Tonight when I set up in the driveway to observe a few doubles my RA drive
started acting strangely. At first I noticed that it made an unusual noise
when slewing in one direction but not the other. Then I noticed that the
alignment was WAY off, much more than I had previously experienced. I then
noticed that the motor was running very unevenly in fast slew RA -- I
thought it sounded like a slipping clutch: the motor would periodically
(twice a second?) speed up (and the ammeter would spike up) and then resume
normal speed. Thinking that this might have something to do with all the
messing with power supplies I had done earlier this week, I switched to 12v
DC (straight from my battery) and then to 18v DC (via the DC-DC converter)
and observed the same behavior. I then did a rough alignment and slewed
back and forth from M4 to M22. Each time it went too far in RA by a degree
or so (Dec was about right). Then, while watching Jupiter (which looked
lousy in the crapy seeing), I noticed that when simply tracking it would
jump a bit every few seconds and simultaneously the RA drive would make a
little tick and the ammeter would spike a little. I measured the interval
between jumps at about 8 seconds (+/- .2 secs maybe). The exact same
behaviour occured in all three power modes. Finally, I noticed that in
CNTR speed the motor would speedup/slowdown just like in fast slew mode but
less violently; it made a sort of ticking sound. Needless to say, all of
this is new; my scope worked fine last week and seemed OK two days ago when
I did all those power measurements.

One theory that occured to me is that I have a broken tooth on some part of
the RA gear mechanism. Tomorrow I'll disassembe the base and take a look.
Meanwhile any suggestions would be welcome.

---
Bill Arnett                 "Science is a way of trying
San Jose, CA  USA            not to fool yourself."      -- Feynman
billa@zNet.com                              <URL:http://www.seds.org/billa/>