The Occultation by Tamara

Sept 15, 2017


Preston map

Preston prediction page

This event had a high rank and was JUST close enough to have me intrigued to try it, especially after my success with the Ninina occultation 5 days earlier, even though it was at a god-awful time of night (4:30am) on a weekday. It would mean essentially nix'ing my sleep for Thursday night, but there were two other declared observers on OccultWatcher, and I knew I'd enjoy loading up my iPhone with some new YouTube lectures on climate issues to listen to on the 1 hr drive to and from Paicines Reservoir.

All went well.... until it was time to align the telescope. The scope went into altitude "runaway upward" whenever I got to the point of giving it a star to do the first of its two-star alignment. This same thing happened for two stars I tried before the Germania occultation, and I wrote it off to bad database info, since it then aligned just fine. But then clearly this isn't the issue, first because it did the illegal move of going to the zenith and then beyond after correctly going to the azimuth of the star. This night, regardless of how many times I re-booted, and which star I chose, it did a "runaway upward" on each one. Was the Dec motor circuit bad? No, I also tried an automatic alignment, and during this it goes left, right, and up and down as it decides it's exact orientation, and it did this just fine. It also found the right nearby town using the GPS, so the GPS was working fine.


With just a few minutes to go, I used the controls to manually go to M38 (which was right next to the target, luckily) and found the target, and watched it disappear for about 4 seconds at about the predicted time. I tried to use my stopwatch to at least get an interval, but it was just too faint to accomplish, and a mis-started D foiled me. So, I got no real timings.


Here's a cut/paste from Christopher Ericson, telescope specialist in Hawaii...


Other Meade LX200 Classic scopes have experienced that as well. However 95%
of all axis runaway problems in under-16" Classics is because the optical
encoder circuit has drifted slightly out of tune and a very slight tweak on
the pot for that axis will get the scope operational. Make sure to mark and
photograph the axis pot before you start messing with it. Turning it the
width of a piece of paper might be enough. The required direction is
unknown until you try.

Another serious issue with all models of the Classic LX200's is the aging of
the tantalum caps in the hand controller, motor driver boards and main
boards. The caps are getting quite old, are handling larger voltages than
they should have been and turn into tiny blowtorches when they fail. Worst
of all, one of the two tantalum caps in the hand controller usually destroys
the keypad ribbon cable when it blows. If you have a Classic LX200 and you
have not already replaced all of the tantalum 5uf 24v caps with 50v
electrolytics, do it right now before you turn the scope on again. Ron
Sampson has a limited supply of membrane keypads if you have one with a
damaged ribbon cable. The ribbon cables are almost impossible to repair.

The 16" Classic LX200 is a completely different animal from the smaller
Classics and uses real Pitman motors and HP HEDS optical encoder assemblies.

The GPS models are completely different too.

And the 16" LX200GPS is completely different from the smaller GPS models.

If you have a Meade LX200 scope that is on the blink, please feel free to
email me for assistance and I'll do what I can to help.

I am not a Meade fanboy but I don't mindlessly bash them either. They are
just one more (affordable) tool to an end.

Personally I primarily use my two Astro-Physics mounts, although I have an
LX200GPS-16 and used to have an LX200-16 Classic.

-Christopher Erickson
Observatory engineer