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ETX 90 gearbox

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#1 jrussell

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Posted 12 February 2024 - 09:59 AM

A couple of weeks ago I opened up my ETX 90 to see if I could fix the problem I'd been having with motor fault errors when trying to get it to align. Cleaned up the excess grease, put it all back together and gave it a trial run. Fake alignment seemed to work, so I took it outside, did a quick and dirty training of the drives and did a quick align. Not exactly on target, but about as close as I expected not having calibrated and not having done a proper training of the drives. Left it on the moon for about a half hour and the tracking lost it, but it was working.

 

Took it out early last week to calibrate and do a proper drive training and my power source was kaput. Went home, ordered a replacement, powered it up with that, slewed to the left a bit, then slewed back to the right, but when I went right the gears started slipping. I opened it up last night to see if I could find the problem. When I opened up the gearbox I found a piece had broken off. I don't know when it broke so I don't know if it's the cause of the gears slipping, or a result of the gears slipping (area circled). In addition to the broken piece, the piece that the screw that helps hold the cover just above the large gear that the motor turns is split so that screw doesn't go in tightly (arrow pointing to it). Would the cover not being snugged down enough possibly be the cause of the gears slipping? Seems odd since it's only one direction that they slip in. I was thinking I would clean both of the broken parts and epoxy them but I wondered if anyone else has had a problem with slipping gears and what they found to be the cause.

 

ETA: The broken piece is the black plastic piece that's sitting on top of the sliver cylinder (not sure of the name of it) in the center of the picture.

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Edited by jrussell, 12 February 2024 - 10:02 AM.

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#2 ArizonaScott

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Posted 12 February 2024 - 10:11 AM

If you're not familiar with this site, there's a myriad of information available for ETX owners. I can't answer your questions but you may find the answers here http://www.weasner.c...x/techtips.html



#3 jrussell

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Posted 12 February 2024 - 10:56 AM

If you're not familiar with this site, there's a myriad of information available for ETX owners. I can't answer your questions but you may find the answers here http://www.weasner.c...x/techtips.html

I checked Weasner's site after I posted here. Saw a couple of similar situations covered but they were different enough from my situation that the solution wouldn't work in my case.



#4 Skywatchr

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Posted 12 February 2024 - 11:59 AM

A couple of weeks ago I opened up my ETX 90 to see if I could fix the problem I'd been having with motor fault errors when trying to get it to align. Cleaned up the excess grease, put it all back together and gave it a trial run. Fake alignment seemed to work, so I took it outside, did a quick and dirty training of the drives and did a quick align. Not exactly on target, but about as close as I expected not having calibrated and not having done a proper training of the drives. Left it on the moon for about a half hour and the tracking lost it, but it was working.

 

Took it out early last week to calibrate and do a proper drive training and my power source was kaput. Went home, ordered a replacement, powered it up with that, slewed to the left a bit, then slewed back to the right, but when I went right the gears started slipping. I opened it up last night to see if I could find the problem. When I opened up the gearbox I found a piece had broken off. I don't know when it broke so I don't know if it's the cause of the gears slipping, or a result of the gears slipping (area circled). In addition to the broken piece, the piece that the screw that helps hold the cover just above the large gear that the motor turns is split so that screw doesn't go in tightly (arrow pointing to it). Would the cover not being snugged down enough possibly be the cause of the gears slipping? Seems odd since it's only one direction that they slip in. I was thinking I would clean both of the broken parts and epoxy them but I wondered if anyone else has had a problem with slipping gears and what they found to be the cause.

 

ETA: The broken piece is the black plastic piece that's sitting on top of the sliver cylinder (not sure of the name of it) in the center of the picture.

Look closer at the intermediate gear right after the motor.  It looks like the plastic teeth are stripped on the "little" gear. But it's hard to really tell from the dark-ish photo.


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#5 jrussell

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Posted 12 February 2024 - 12:46 PM

I'll try to check that tonight. Thanks.


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#6 jrussell

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Posted 16 February 2024 - 10:53 AM

Well I have an update. Last night I opened the gearbox back up so that I could epoxy the broken piece back into place and to epoxy the hole for the other screw as well. As my luck would have it, when I was putting the broken piece back into place I found that the piece it was needing to be epoxied back to was also broken and pretty much hanging on by a thread. So, I epoxied that back into place as well, then noticed there was a small piece between them that had broken off doah.gif . Luckily found that and added that piece back in as best as I could. After everything had set I put it all back together. I was going to leave it, but I figured I might as well give it a try. Got it powered up and with my expectations set pretty low I gave it a try. It turned left and right. There was a bit of an odd noise a couple of times but the gears didn't skip. So, is it fixed for a minute, or fixed for a lifetime? I don't know yet. I'm going to try to get the drives calibrated and trained this weekend, and hopefully get it out to test the goto (less important), and the tracking (really the only reason I'm going through all the trouble). If it turns out the repair fails I'm pretty sure I'm finding something else to mount it on All that said, the forecast for the weekend went from clear to cloudy so....


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#7 jrussell

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Posted 21 February 2024 - 10:41 AM

I finally was able to take it out yesterday afternoon to calibrate and train the drives. It still makes a little noise like the gears are trying to skip if I'm slewing fast, but they never actually did skip. Got the drives trained, then ran an easy alignment. Just accepted the targets as being centered since it was still daylight, then since it was visible chose the moon as my target. It wasn't centered in the eyepiece, but since I wasn't super accurate in putting it in the home position, and not being able to see the alignment target stars I didn't really expect it to be. Just the fact it was even in the eyepiece made me happy. I let it track for a few minutes and  it moved out of the center again (expected), but it all seems to be working correctly. I turned it off, then decided to give it another try, so turned it back on, ran the easy alignment, and went to the moon again and once more it all worked. So it would seem I fixed the problem(s). I'm going to take it out at night sometime in the next few days to test it more thoroughly.

 

Ultimately what started all this were the motor fault errors I was getting when the mount would just keep turning until hitting a hard stop when doing an alignment, and honestly from the best I can tell the excessive amounts of grease on the gears seems to have been the source of that happening. Fortunately none of the gears seem worn or broken so I'm still not entirely sure why they still try to skip if I have the rotation speed up high. When it was slewing during alignment it didn't seem to be trying to skip, so I guess as long as I don't set the speed too high that won't be a problem any more. I've really been hoping to get a lot more use out of this scope and it looks like I'm finally going to be able to fingerscrossed.gif


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#8 jrussell

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Posted 28 February 2024 - 04:23 PM

Finally get my EC working and now I find a 90 PE for a good price crazyeyes.gif

 

ETA: and just like that it's gone lol.


Edited by jrussell, 28 February 2024 - 04:57 PM.

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#9 jrussell

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Posted 05 March 2024 - 10:57 AM

Took the 90 out for some field testing over the weekend. Had hoped to get some solar observing done, but by the time I got set up some clouds had moved in. Clouds were a problem off and on through the evening but the ETX soldiered on. Alignment was no problem and Jupiter was my first target. wasn't centered and for some reason when I'd try to get it centered the ETX would move it back to about 11:00 in the EP. Was windy so the seeing wasn't great, but it died down for a while. Tracking worked no problem though over time the goto wouldn't get the target in the EP. Got it on the Pleiades and was one of the best views I've ever had of it. A couple of other guys were out with me and were both very impressed with the view. Finally had to give up early because of clouds. Afterwards I remembered that when I had done my alignment I just accepted the targets were in the EP without looking because it wasn't quite dark, but Jupiter could be seen. After it got dark enough I should've done another alignment and checked the target stars. Overall though I thought my shakedown evening with the newly repaired ETX was a big success. Getting out again this weekend for more testing with higher hopes for this scope than I've had before.



#10 Thrifty1

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Posted 05 March 2024 - 11:23 AM

Glad to see your hard work has paid off on this ETX - good job!!   When slewing to a target and centering it, try to finish by only moving up and to the right with the keypad.  This will better engage the gears.  Otherwise it may drift as the slop in the gears is taken up before the gears are fully engaged.  


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