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Play in DEC Position


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#1 midcon07

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Posted 09 April 2007 - 12:12 PM

I have a LXD75 8" SCT (my first scope) which I've had for a couple months but with very limited time to operate it so I'm definitely a newbie. I'm confused about a couple of terms; backlash and periodic correction. I actually don't know if I'm experiencing either one so here are the situations. 1.The scope is just sitting there, no power, both the DEC and RA locks are locked. I have a very small movement (play) in the DEC; the R.A. is tight as a drum. 2. Scope polar aligned, and Autostar 3 star aligned. It seems to take a long time for the scope to respond when I select a slow slew speed, say 3 on the keypad. No problem with fast slew speeds. Thanks for your help.

Jerry

#2 Guest_rtanton_*

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Posted 10 April 2007 - 08:52 AM

Jerry, it sounds as if one of the gears on the dec may have loosened.  If you remove the key shaped port on the motor housing, you can see any slip.  The most common cause (~85%)is a loose gear set screw.  To repair you wll need to remove the motor assembly (two allen screws on the top) nd retighten the setscrews.  These are very small metric allen setscrews.  A second cause could be worm gear slip.  This is bit trickier as there are three screws hold the worm assembly.  Loosening only the center allen screw very slightly (1/16 turn) will tighten this.  If it is too tight, the center screw needs be turned in...but ONLY after loosening the two outer allen screws.  Turning in the center without this step is likely to strip the center threads in the casting.  This procedure requires a bit of trial an error as the three screws interact with each other, but when properly adjusted you will see a big improvement at those slow slew speeds.

Russ

#3 midcon07

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Posted 10 April 2007 - 04:32 PM

Thanks Russ, I'll check that out tomorrow. Appreciate it.

Jerry

#4 p_houlahan

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Posted 21 April 2007 - 12:05 PM

I have a similar problem but with the RA axis.

Do I have to remove the whole motor assembly using the allen screws or can I get the front half off the black plastic drive cover to take a look? I tried loosening the 2 screws that seems to hold the two halves together but I still find resistance when I try to take the front plastic cover off. Am I missing something here? Should it just pop off?

TIA

Padraig

#5 Guest_rtanton_*

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Posted 21 April 2007 - 08:31 PM

The motor housing is removed by loosening the allen screw on the back end of the scope (inside a recess near the polar scope)...a bit hidden.

Russ

#6 midcon07

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Posted 22 April 2007 - 06:04 PM

Well Russ your 85% probability was right on. The first thing I saw was the amount of play in the gears and then found the set screw was indeed loose. Also checked the R.A. side and found the same. I'm amazed the scope was performing as well as it was. Thanks for the help.

Jerry




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