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    Default ETX 70, very jerky target during sidereal, do motor gears ever need lubricating?



    Hello, I acquired a used ETX 70, Autostar 494. After aligning properly in ALTAZ, During the centering of Jupiter with the arrows, the target jumps around. If I press right arrow Jupiter may first jump to left and then start going right (it is set to move right with right arrow). Same with up down keys. Once centered, the sidereal motion of the motor is also jumpy (lot more than just the seeing disturbance). The object randomly jumps to any direction back and forth as if the gears are having problem / catchy etc. That is a continuous problem, not just at a certain spot. I am using fresh 6AA batteries that read 8.6v.

    My guess is that the scope was not used for few years. Do the gears ever need lubricating? Could the motor mount inside be slightly loose? If yes, is there a link on "how to check it/fix)"?

    Thanks.

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    Default Re: ETX 70, very jerky target during sidereal, do motor gears ever need lubricating?

    The jerky movement when trying to centre sounds like you have the slew speed set to high. Press the speed/? Button briefly changes the speed, 1 is fastest 5 is slowest dont hold too long youll get the help menu. The moving after centering sounds like it needs a train drives found in the setup settings. Try google to find an online manual or try check the weasner.com site for info on anything etx there is some good info there. If it had been sitting for a long period the grease may have hardened a bit, the weasner site may have info on lubricating or first you can try do a couple of revolutions stop to stop in both directions to redistribute the grease on the worm and gear.
    Al

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    Default Re: ETX 70, very jerky target during sidereal, do motor gears ever need lubricating?

    Alval, Thank you.

    I took the scope out tonight again. The motor does not seem to have any problem when slewing to seek an object. Say when it is doing the two star alignment, it is going in one direction smoothly. But once the object is located by the auto system, then to center the object I have to use the arrow keys. I had the slew speed set to lowest, which is 2X (like 64th part of 1 degree. With that speed set, the right and left arrow worked fine, very very slow motion movement, would take perhaps a minute or 2 of constant holding the button to move the object to center. But the up down arrow worked very fast. With the 20mm eyepiece, one push of arrow button would move the object about 1/3 the screen. And as soon as I let go the button, the object spontaneously moves back most (not all) of that distance back in the opposite direction (and I can hear the motor sound as this happens). This happened repeatedly. And then some time, it would function at the same speed as right/left arrows. But most of the time, it was the fast speed. I had really hard time centering object in the up down direction because of this. I cannot think of what type of defect would cause this type of behaviour. If it was gummed up gears, then it should be difficulty in all motions not just the centering type controls. Any ideas? Thanks.

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    Default Re: ETX 70, very jerky target during sidereal, do motor gears ever need lubricating?

    What you are describing sounds like rubber banding a common issue with etx. If you search the term there is a lot written about it and the fix is generally to do a train drives and train motors. If that doesnt fix it there may be an encoder issue with dirt or grease on them. Search the weasner site there is more written by better experts than me on how to do it for your particular etx. The drive training is pretty simple with a reticle eyepiece during the day.
    You may find info about the 12 volt power source as well.
    Al

 

 

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