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yeti monster

Skymax 90 stripdown

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After repatriating my skymax 90 to China, I noticed that there was a blurryness to the image. Looking down into the primary it was clear that there was contamination on the mirror so I decided it would be worth stripping the scope.

I'm uncertain as to how similar the other Maksutovs are to this 90mm model, but I'm sure that they aren't too dissimilar.

Firstly I had to remove the corrector plate, which was just a case of taking a firm grip of it and unscrewing. There are 2 small holes for a face key (or 2 small pins and a bar) but I didn't need these.

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Once the corrector plate is removed then the focuser knob needs to be released by removing the 2 small grub screws:

75039841e5c3b84cce198e04f955140d_4933.jpg?dl=1273020852

With these out, the primary and focusing screw can be withdrawn through the front of the optical tube.

With the primary out, the focuser tube retaining capscrews need removing (better to position the OT vertically and mark the positon of the endcap in relation to the OTA for correct reassembly):

2dd8e20ab7b3efdec4ed29e3f0590ff5_4935.jpg?dl=1273020852

The focuser tube is then free to be withdrawn:

2bafa8096529c913d57033bbdb0c69c1_4929.jpg?dl=1273020852

The naked OT showing the collimation plate:

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Providing the collimation grub screws have not been disturbed, there should be no need to re-collimate the focuser tube, a star test post rebuild will show up any mis alignment.

There should be an o-ring seal between the OT and the focuser tube end cap, mine was broken due to becoming nipped during initial assembly:

ff9c1af862b2204b24ab077b96c64daf_4925.jpg?dl=1273020852

How it works: The focusing of this scope is achieved be moving the primary mirror up and down the OT along the focuser tube, by means of the focuser knob, collimation grub screws alter the attiude of the focuser tube and thus the attitude of the primary as it sits on the focuser tube:

512831a9757d3488ef560eba450543ed_4928.jpg?dl=1273020852

The secondary mirror is integral to the corrector plate and will benefit from cleaning if required:

64c0263560f743d72901925a2ef0cbc6_4930.jpg?dl=1273020852

To remove the focuser adjustment 'nut', this stop screw has to be removed:

ebdbdd5412cec933eeea7ad89978f681_4932.jpg?dl=1273020852

Which will allow the focuser adjustment thread to be cleaned of grease.

Once all the parts had been disassembled, I set about removing almost all trace of the nasty black, ink like, grease from every component, which seems to have got everywhere. Leaving only a light film of lubricant on the parts which need it, I then re assembled the scope, in true Haynes manual fashion, this is a reversal of the dismantelling proceedure. When refitting the focuser knob, the primary needs to be pushed in as far as it will go before tightening the focuser knob grub screws, to ensure that there is as little play as possible. When installing the the focuser end cap, don't forget to reinstall the o-ring seal (I have to locate a replacement for mine, but was able to keep it in position during the assembly).

Edited by yeti monster

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When i had the 127 version i went as far as removing the focussing knob and then stopped.

Looking at your photo's, I'm now pleased I did.

Excellent set of photo's which will be a great help to anyone who feels brave enough to tinker.

Paul

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It is far easier than stripping a conventional Newtonian scope. I suppose, as my job is to dismantle things which others are feared to approach, such tinkering is more like therapy to me.

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Good post here.. thanks for sharing. I always find if you take your time and dont force anything, then tinker.. its the only way to learn. Mind you only do this if required, dont just do it for fun.

Rob

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Thanks YM,

I'd wondered about the anatomy of the SW Maks.

On the 180 Pro there are four rivets around the circumference, just behind the corrector plate - I'm not sure but these may anchor it. There are another 4 at the back, going through the side wall of the end cap and almost certainly securing it.

Bet the 180 Mak would be a right so 'n' so to do a tear-down on.

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I have to say I find therapy in taking bits back to their component parts (dad used to say I would strip down the universe if I were bored enough) but I am nervous of a 180 MAK as well.

I keep getting it out - considering it - then think 'nah' leave well alone :D

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Astro_Baby,

So you went and got yourself a Skymax 180 in the end?

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Thanks for the long-awaited general MAK anatomy lesson - Fascinating! I have (un)screwed the corrector plate of the 127 to drill some new holes in the OTA etc. I also needed to remove the focusser knob, to measure up for a DIY electric focusser. Came within a smidgen of watching the brass shaft etc. disappear into the OTA(?). FWIW I do now remember to keep OTA horizontal, when the knob is removed... :D

On the 180 Pro there are four rivets around the circumference, just behind the corrector plate - I'm not sure but these may anchor it. There are another 4 at the back, going through the side wall of the end cap and almost certainly securing it.
Heheh. To be strictly accurate (at least on the MAK 150 PRO) they are M2.5 "hex bolts" - I gave ONE [at the corrector end] a slight experimental twist, but that's as far as my courage / disgression allowed. :p Edited by Macavity

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Heheh. To be strictly accurate (at least on the MAK 150 PRO) they are M2.5 "hex bolts" - I gave ONE [at the corrector end] a slight experimental twist, but that's as far as my courage / disgression allowed. ;)

Yuup! You're right. Dead tiny hex bolts.

Should've double checked before posting. :)

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Well I kind of inherited a SkyMax 180 ED Pro - its a very long story and this scope has had more owners than you would believe. None of them yet (me included) have ever gotten to use the wretched thing. Its like pass the parcel.

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Should've double checked before posting. :)
Not at all! I'd've probably drilled 'em out by now. LOL. I do casually wonder if the end cell is threaded - like the smaller MAKs, and they just help locate it consistently. Or maybe indeed they do hold the whole thing on... ;) Edited by Macavity

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Nice work, thanks for posting the photographs - Very useful. I managed to buy myself a Skymax 90 on Fleabay at the weekend for peanuts, complete with aluminium case & tripod etc.

I made a clean area in the kitchen this afternoon, and following your post I stripped the Skymax down and gave it a good clean. It was also full of black grease, flaming nightmare to get clean I can tell you!

Unfortuntely mine also as a split O Ring, thankfully it's gone back together perfectly and a dab of superglue work a treat for repairing the O Ring.

End result - I now have a lovely clean Skymax 90 in perfect condition.

Many thanks

Mark

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I think I was watching that one, a goto?

I'm glad it went for a bargain price and I really glad that my report was helpful to you.

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Just had another look at this thread, how is the front of the Mak held in place ?.

Is it a push fit or is it screwed into place like the rear.

Paul

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Excellent and very useful. I was having this very conversation about collimating Mak's with Steve at the last Adur meeting. Is it the larger screws that hold the rear plate on and the small the collimating screws or vice versa ?

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Paul / John,

The front lens housing screws off, the rear is held on by the large allen bolts (three smaller one's are for collimation).

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