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Nexstar 4GT optical system dissassembly question

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#1 Peder_y2k

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Posted 23 June 2012 - 11:13 AM

With no visible screws, how does one dissassemble the corrector plate(lens)from the metal tube? I need to re-glue the meniscus mirror baffle and clean the primary mirror, but don't know how the corrector end is fastened. Is it glued together, or are there threads holding the corrector assembly to the tube?
Thanks for any help........
-Pete, in Tacoma WA USA

#2 Tel

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Posted 23 June 2012 - 12:08 PM

Hi Peter,

Welcome to CN and to this particular Nexstar forum ! :bow: :bow:

Perhaps this photographic depiction of the 4SE's disassembly, reassembly and collimation provided by our good CN friend and colleague, "ibase", (Hernando from Manila), may help ?

https://picasaweb.go...4SEDisassembly#


Best regards,
Tel

#3 Peder_y2k

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Posted 23 June 2012 - 05:58 PM

No help, as the 4GT has no screws like the 4SE. As I wrote, the tube has no visible screws holding the corrector end assembly to the tube. Either it is threaded on, or glued on. If threaded, then a strap wrench could unscrew it.
-Pete, in Tacoma WA USA

#4 Midnight Dan

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Posted 23 June 2012 - 08:38 PM

Hi Pete:

From Hernando's photos, it appears that the 4SE also does not have any visible screws holding the corrector in place. The only shot that really shows the front end in the last one. The others that show screws are showing the rear end where the focuser and primary mirror are.

If your scope is like the 4SE, you may have to remove the rear cell as Hernando did. You should be able to access the inside of the corrector plate from the rear. It may be a little inconvenient working inside the tube, but that might be the only way. From the look of it, my guess is that the front cell is glued in place.

-Dan

#5 Tel

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Posted 24 June 2012 - 02:50 AM

My sincere apologies Pete, I totally misread your 'scope's identification type: (I read 4SE instead of 4GT) ! :bigblush:

Dyslexia rules ! ........ KO ?

As Dan advises though, I wouldn't have thought that there was that much difference in the basic design between the 4SE and its close predecessor, the 4GT; if at all. (?) :idea:

Best regards,
Tel

#6 Peder_y2k

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Posted 24 June 2012 - 11:18 AM

KO for sure.
Now the electronic slew control is malfunctioning requiring a power restart to begin again. Using AC adapter rather than batteries. Unlugged and examined all circuit board quick connections, and found clean and tight. Should I inspect the hand unit internals?

#7 Tel

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Posted 24 June 2012 - 11:26 AM

Hi Pete,

Switch to a set of AA batteries first.

If these work; suspect your external power source. It may well be that your cord lacks continuity or that its end fitting at the mount's jack plug is a poor fit; (often the case). Jack plug fittings are regularly supplied with an internal diameter of 2.5mm. However the pins on these 'scopes ideally require a jack plug of 2.1 internal diameter, (5.5mm outer) to ensure a snug fit. Failing this to hand, the receiving pin on the mount may be spread, (carefully) to make a tighter fit.

Best regards,
Tel

#8 Midnight Dan

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Posted 24 June 2012 - 11:30 AM

Hi Peter:

Sounds suspiciously like a power problem. Since you're using an AC adapter, I would suggest getting a set of brand new, fresh batteries and installing them in the base. If it works, then the problem is with the AC adapter connection.

Depending on where the adapter came from, it may not be the exact right connector. The correct one has a 5.5mm exterior diameter, and a 2.1mm interior. Some adapters come with a connector that has a 2.5mm interior. In most cases, this wrong connector will work, but will be unreliable and occasionally lose connection for an instant, which makes your electronics go wacky ( <-technical term). :grin:

You can try to improve connectivity by spreading the halves of the split pin inside the connector in the base of the scope. You can do so GENTLY with a small knife. Don't go overboard or you risk breaking the pin.

-Dan

#9 Skip

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Posted 24 June 2012 - 11:49 AM

:lol: What is it they say about great minds?! Posted 4 minutes apart and you guys wrote almost exactly the same thing! :rofl5:

#10 Tel

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Posted 24 June 2012 - 12:39 PM

Or Skip, as in Germany, the proverb goes.... Zwei Ochsen, ein Gedanke ! (Two Oxen, One Thought) !

I'm not absolutely sure it's at all flattering though ! (?) :idea:

Best regards,
Tel

#11 Midnight Dan

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Posted 24 June 2012 - 03:42 PM

Yes, I believe our posts crossed in the ether. Oxen are like that! :grin:

-Dan

#12 Peder_y2k

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Posted 24 June 2012 - 08:49 PM

I switched power supply and used my field battery pack and that worked. Problem solved. The AC power supply terminal I had been using was indeed the incorrect size for stable contact.
Now to get back to airing out the room from all that oxen outgassing.
Once that is complete, I can get back to figuring out how to remove the corrector plate from the tube on my Nexstar 4GT
-Pete, in Tacoma WA USA

#13 Midnight Dan

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Posted 24 June 2012 - 10:22 PM

Excellent! Glad it works now. And us oxen will try to refrain from any more excessive outgassing!

:cloudy:

-Dan

#14 Tel

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Posted 25 June 2012 - 01:42 AM

Good result, Pete ! Good luck with the disassembly.

(I'm off for a quick graze and a wee bit more methane production) ! :bigblush:

Best regards,
Tel :gramps:

#15 Peter9

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Posted 25 June 2012 - 04:19 AM

As the Bull said, I want to stay here for Heifer and Heifer and Heifer. :roflmao:

Regards. Peter.

#16 Sameer KM

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Posted 21 November 2012 - 06:31 AM

Hi Pete. Any luck with the diss-assembly? It would be great if you could post some pics. I am also looking forward to service my 4GT

#17 Tel

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Posted 21 November 2012 - 07:37 AM

Hi Sameer KM,

A very warm welcome to CN and to this forum ! :bow: :bow:

Please don't quote me because my recall is incomplete, but I seem to remember since the original post here and from some information source, that the primary mirror cell of the 4GT is threaded onto the tube. The likelihood therefore, is that the corrector plate is similarly attached.

Perhaps try unscrewing either/both, (gently) ?

Best regards,
Tel

#18 Arthur Dent

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Posted 21 November 2012 - 12:42 PM

As the Bull said, I want to stay here for Heifer and Heifer and Heifer. :roflmao:

Regards. Peter.

:foreheadslap:

Art

(PS That reminds me of a rather rude joke Peter, which I cannot share in an open forum!)

#19 Skip

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Posted 26 November 2012 - 12:20 PM

As the Bull said, I want to stay here for Heifer and Heifer and Heifer.


:foreheadslap::foreheadslap:

#20 russdirks

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Posted 14 January 2013 - 02:18 AM

For anyone hitting this thread with the search function, I can confirm, as the owner of a 4GT, that the front corrector cell is threaded on.






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