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Old 24-09-2019, 10:19 AM
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The_bluester (Paul)
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Celestron focus motor issues

I ran in to an issue last night with the Celestron focus motor on my SCT which I have resolved, but I thought I would post it here in case it is useful for someone else later.

I was running into issues with inconsistent operation, I had put it down to driver issues initially as it would work sometimes and then exhibit some odd behaviour, like not responding then suddenly moving quickly to the requested position. Last night it just stopped moving at all.

I removed it from the scope (which was difficult as the machine screw to release it from the focuser shaft was in a tricky spot and it wouldn’t move) and discovered that the retaining nut which holds the shaft that actually couples to the SCT focus knob had come very loose. With the nut loose the shaft was moving out of its support bearing and the large diameter gear on that shaft was binding on the housing and stopping the motor from moving, a quick tweak up with a spanner and all is back to normal. The nut is a very thin alloy one, I think I will redo it shortly with a drop of low grade loktite or it is likely to happen again.
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Old 06-08-2020, 09:12 AM
Spidy (Phil)
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Hey Paul. Just came across your old post. I put mine on the scope for the very first time last night. The actual installation part went well, but when I tried to run the calibration procedure it sounded like the motor was hitting some resistance. So after removing it and trying again three times, I decided to risk it and let the routine run till the end.


After completion, I manually adjusted the motor with hand controller and it acted and sounded like every other Youtube video out there.


Thought I'd bring this up as Celestron's instructions are not the best out there. My best guess is the routine was rotating slowly so it doesn't exceed the focuser's limits??????


Another point I took away from your experience is the Set Screw came with blue locktight already on it. I'm sure I removed most of it when I removed the focuser three or four times. So I guess I need to be aware of this in the future and keep an eye out.


I hope this also helps somebody out there.
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Old 06-08-2020, 01:52 PM
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The_bluester (Paul)
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What I have noticed is that it is quite difficult to ensure that the focus motor is straight on the shaft (This might be better on the scopes with a larger diameter focus knob that does away with a plastic insert) and the focus knob itself does not run 100% true, so you can hear the motor speed change at the same points every revolution.


I don't recall the calibration routine running at any different speed to normal focus action, but they might have done firmware changes since mine was built as mine is a quite early one.


The loose part I was talking about is actually the lock nut on the end of the shaft through the focus motor body rather than the set screw that locks it to the focuser shaft itself.
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