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"Grumbling" ETX-70

Meade mount
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#1 JoeVanGeaux

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Posted 27 May 2020 - 09:39 AM

I discovered a few previous posts that remark on the grinding noises made in the ETX-70 (and maybe others?).  Some of the posts discussing this are reassuring.  Thanks!
 

I have both the ETX-90PE and an ETX-70.  The 90 runs very quietly but, as often described, the 70 "grumbles"...  a lot!  Its very disconcerting and it appears its something that's generally accepted to be in "the nature of the beast".  However, this seems this would be like constantly running a car engine with the "check engine" light on all the time... and at some point its going to be correct but I won't know it!

Has anyone determined the nature of the grinding noises?  Poorly meshed gears?  Lube-less gears?  Loose screws or, maybe, just sloppy clearances in the gear mountings?  (Slew speed does not seem to matter, by the way.)

I recently acquired the ETX-70 scope and gave it a cursory "restoration" with the intention of giving it to one of my brothers who has some OCD issues (real, not the kind we all often kid about) and I'm afraid (almost certain) he will attempt to "fix" the grinding noises and this will result in a disaster.  I didn't know about the noise issue with these scopes; otherwise, I would have looked into other "manual" options.  I only reluctantly went for the "goto", electronic scope because I thought this would be encouraging ... but I'm now thinking long and hard about giving this scope as I don't want a bad experience to kill the hobby that I know he'd enjoy (as he did when we were kids).

Any guidance or insights would be helpful.

All the best!

Joe


Edited by JoeVanGeaux, 27 May 2020 - 09:40 AM.


#2 sg6

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Posted 27 May 2020 - 10:27 AM

Had one for 20 years, still grumbles, although quietly, all the time. Has never got worse or better.

Not sure if there is a reason other then the way it is constructed.

Bought one for a fiend and I think that grumbled quietly also. So as said it seems just to be part of the nature of the scope.

 

Actually unsure if I would like a quiet one, at least I know it is running.

Haven't use the ETX 105 for so long I cannot recall anything about that. Probably quieter.

 

Internals have to be a little different as the 90/105/125's all have end stops, the 70 and I assume the 80 go round and round.

 

Have just assumed it is the motors used, sounds a motor produced noise. Not looked but I might guess that the Az motor has a gearbox on it and that the combination is the cause. If so very likely nothing can be done even if you dismantled one as the pair are likely a unit.


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#3 JoeVanGeaux

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Posted 27 May 2020 - 11:41 AM

Thanks, sg6!

I have been tempted to open it up just for a peek.  However,t since I had repaired my ETX-90 mount before I am reluctant to just open it up only for grins.  I don't want to chance tearing up some wire harness or loosing screws (again).

I also wondered about the the range of motion for the azimuth, since I read somewhere that  the ETX-70s do not have a "hard stop" - I haven't confirmed this.  So, you are suggesting it may go around 360 degrees endlessly if all else is working?  I first oriented my ETX-70 as though it had a hard stop after hesitantly rotating it in the same general (and estimated) orientation as my ETX-90... then wiped my brow when it appeared I didn't tear out any wires or gears and left it alone after it appeared to roughly calibrate itself.  It seems to "goto" and track well enough (of course, noisily) and I always stop it in the "home position" and return it to the same marks I made on the driveway for the tripod before re-starting... lest I be tempted to over-rotate the mount and chew-up the wires.

I did catch myself approaching a near panic once and shut off the scope when it looked as though the mount was going to over-rotate when slewing to an object taking it in the high 300s of azimuth, tho!  Until I understand its operation I will avoid objects in that region of the sky!

I've seen a few videos showing some repair or another to the ETXs but noting showing details "under the hood" of an ETX-70 that convinces me of its drive mechanics.



#4 David Castillo

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Posted 07 June 2020 - 10:56 AM

The noise is coming from the metal gears of the drive servos. They are digital and are constantly sending back a signal to the drive logic to properly move or correct the scope in alt/az as it tracks or slews. It's normal, and don't think about lubricating the gears, as it won't accomplish much. The servos's noise will become erratic or more obvious if the power is dropping. Just help the drives out and train them with each battery change to make sure the scope tracks accurately. Don't let the noise bother you, just enjoy the wide-field views that your 70 offers.


Edited by David Castillo, 07 June 2020 - 11:00 AM.


#5 jhart

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Posted 19 June 2020 - 07:44 PM

I have an older LX200 that grumbled loudly -- tracked well but complained a lot from the RA gears in the base.  Based on the recommendation from Meade I removed the scope and forks from the base, cleaned the old grease from the worm and circular gears (the ETX gear set-up looks to be very similar), applied white lithium grease, and reassembled.  It is much quieter now.




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