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Help me rebuild my ETX 125

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#1 vdog

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Posted 06 September 2021 - 05:56 PM

So, sometime during the long period I wasn't using this scope, it got messed up.  As in, the entire-mirror-assembly-loose-in-the-tube messed up.  I have theories involving young children and tempting, oversized focus knobs, but it what ultimately matters is that what I thought would be a quick fix quickly turned into a complete rebuild.

 

In this picture, on the left, I think I have the focus knob assembly and rear plate correctly reassembled..  The rear plate wobbles so I imagine I need to screw in the collimation screws that align with those three holes?  The only thing that makes me hesitate is the "don't touch" red paint on the heads of those screws (not pictured). 

 

What has me really scratching my head is that the mirror was not attached to the plate.  I see no trace of glue that wore out; it's like there never was anything holding the mirror in place.  Am I missing something?  Should I cement it to the plate?  Seems like it could just shift around otherwise.   

 

Thanks!

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Edited by vdog, 06 September 2021 - 06:01 PM.


#2 Van Huynh

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Posted 06 September 2021 - 06:11 PM

Take a look at this YouTube video.

Looks like you are missing the retaining ring that holds the mirror in place.


Edited by Van Huynh, 06 September 2021 - 06:17 PM.

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#3 vdog

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Posted 06 September 2021 - 07:08 PM

Thank you!

 

After watching the video, I found the retaining ring wedged into the secondary housing.  Now it makes sense. 

 

I've reassembled it with a 3D-printed back and helical focuser I picked up online.  I'll test it out, but I have my doubts the collimation survived the upheaval .  Fortunately, the new back allows access to the collimation screws, so that may be my next project.

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