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Problems with the DS Motor


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#1 thunderbear

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Posted 15 December 2013 - 12:52 AM

You all will have to forgive my lack of knowladge on telescopes. I will try my best to explain my problem.
I bought a 3rd hand Ds telescope. From the things I have read,.it is a Newtonian reflector. It has no model number on it. It just say Telestar by Meade. The lenses are fine. I have a 494 handbox that just came in the mail. I plugged it into the computer control and turned the switch to On.
When the led screen lit up, it first said "Initializing" Then tried aligning. I could hear the motor running, but it wasnt moving the scope. So I took the "can" apart & everything looked ok except one of the gears' teeth were worn down & there was a little plastic tube that looked like a screw that wasnt moving. This tube ran horizontally and had a metal rod through it with tiny little plastic gears under it. There was also a metal arm that looks a whole lot like a clutch. It was very loose and had rubbed grooves into the metal "can" lid. I used the directional buttons with the motor exposed and all the gears were moving except the plastic tube srew looking thing.
I need help with this. Any advice would be greatly appreciated. Im needing it fixed this week. Thanks, Chrissy

#2 MistrBadgr

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Posted 15 December 2013 - 10:09 AM

Hi Chrissy!

Welcome to the forum!

The tube with the threads on it is the worm gear that is supposed to mesh with the big bull gear that is fixed to the inside of the bottom bell, around the center post. If the worm gear is not turning, then it must not be meshing with the little gears between it and the motor. There should be another gear on the same shaft as the worm gear that should be meshing with the gear shaft next in line toward the motor. Not being able to look at it, it is kind of hard to say.

You might try looking at it again and running the motor and see if the other gear on the worm gear shaft is moving and if it is actually meshing with another gear. If it is moving and the worm gear is not, then it has come loose on the shaft somehow. I am not quite sure how to fix that, other than putting in a new worm gear shaft. Such a shaft would have to come out of a different mount. There are no spare parts available other than from another mount that is broken in some other way.

That whole framework is supposed to be pushed up against the bull gear attached to the center column in the bell. There is a stainless steel leaf spring that is supposed to keep the gears pushed together. Then, if something really stalls the scope, the leaf spring can flex to allow the worm gear to pop from one bull gear tooth to the next as the worm gear turns. There really is a loud popping sound when this happens. That leaf spring can loose its tension over time.

When putting the mount back together, a certain gentleness and care has to be used to get the worm gear and bull gear meshed properly. It is possible to jam the two sections together in a way that jimmies the whole gear frame out of the way. That is about the only way I can see that there could actually be wear marks in the bell.

There is also what I call a thrust post that is held in place on one side of the gear frame to keep the whole frame from thrusting in that direction when the worm gear tries to move the scope. In older mounts, it is hard to get things tight enough after that post is loosened once to keep it from turning out of the way. In the most recent version of the mount, the bottom of the post was changed to keep it from moving with the screw in place. Older versions of the scope are normally black with maybe a white or red band around them. The Generation II mounts will have silver gray plastic on the arm or they may be all white.

I am in some family medical things right now and am not looking at the forum as often as a normally do, but look again at the gearing to see the things I mentioned above. It will take me longer than usual to get back with you. If you can tell me which mount you have, all black or with silver gray or white plastic, I will pull apart one of mine to look and see the parts you are talking about. We can see if we can work through this and if there is a reasonable solution.

Bill Steen
Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma

#3 thunderbear

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Posted 16 December 2013 - 10:40 AM

Thanks, Bill.
What you are describing sounds exactly like the guts of my mount. The metal thing is the thrust post. It has a notch in one side like its supposed to hold that frame in place. Now, the frame itself moves when this post is loose. Is the frame supposed to move?
Thanks again for taking your time to read & reply. I hope things turn out good for your family!

Chrissy

#4 MistrBadgr

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Posted 16 December 2013 - 08:41 PM

Hi Chrissy,

Ideally, the frame should not move at all. Since it is made of plastic, it will flex a little. The post should be pushed as close to the frame as possible without binding things up and causing the scope not to move. There is a little spot near the top that sticks out and pushes against the frame. Sometimes, the post will rotate when it comes loose and can confuse you as to its proper position. You have to tighten up the screw as tight as you dare without striping the threads. You might try a drop of glue of some sore under the post, then tighten up the screw and let it set until the glue dries up. I do not know if you could work fast enough to use superglue. There is a material called LocTite that you might be able to get at an auto supply store that is made specifically for that kind of situation.

At this point, I do not know if that is the only thing wrong and that getting the thrust post back in position will solve all the problems, but it is certainly a good place to start. You might also want to look the frame holding all the gears and make sure that it is not broken. I have broken one before when taking gears out to smooth some of the teeth. If that happens, the mount is history.

Hope this helps,

Bill
Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma




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