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12" LX200 EMC Stiff Focus Knob

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#1 Adam Brunette

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Posted 30 August 2013 - 08:03 AM

I have an older 12" LX200 EMC that seems to me to have a very stiff focus knob. My prior experience was a much newer ETX-70. Not much to compare there, but the focus knob is much easier to turn.

The 12"'s knob isn't sloppy or grinding, it just feels like it needs alot of effort to turn. I didn't realize it was too much till I tried installing a robofocus. While trying to calibrate the full travel of the focuser in the robofocus, I noticed the clutch was slipping alot.

My mechanical background is telling me that the grease is old and drying up needing to be cleaned and replaced. I don't just want to go ahead and do this without consulting the forums.

BTW, this unit is before they put the focus lock on the mirror.

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If anybody has any suggestions I would really appreciate it.

-Adam

#2 Skywatchr

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Posted 30 August 2013 - 11:56 AM

Hi Adam, yes it is possible the grease is a little stiff. And I believe the mirror in the 12" is spring loaded. Try running the focus knob all the way CC and CCW several times to re-spread the grease out. If that doesn't help much, then I guess a dis-assembly, cleaning, and re-greasing is in order.

Jeff

#3 *skyguy*

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Posted 01 September 2013 - 08:21 PM

Adam,

I've had a Robofocus installed on my 12" LX200 EMC for the past 10 years. I was unaware that there was a clutch included in the Robofocus system ... unless the newer models now have it? When you say "slipping" ... do you mean the geared plastic wheel is moving while the scope's metal focusing knob remains stationary?

Jim

#4 Live_Steam_Mad

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Posted 12 September 2013 - 10:54 PM

When I dismantled my quite old Meade 7" Mak ex-LX50 to remove the disc weight I found that the red LMX style Meade Petroleum based grease had turned into the consistency of a wax and there was nearly none left whatsoever on the baffle tube anymore, it was nearly all at the baffle tube end, behind the mirror. I removed what was left and relubricated with Rocol MTS1000 which seems to have removed the large image shift problem as well. But I have yet to see if the grease is too viscous in winter. MTS 1000 is a fairly thick grease.

What is your mirror shift like on your LX200? e.g. by how many Jupiter diameters at say 250x? My friend Jon H's LX90 ACF 8" has just started to develop image shift of 1/2 Jupiter diameter after 3 years of use nearly every clear moon free night. Focusser on it still has zero detectable backlash though.

Regards,

Alistair G.

#5 David D.

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Posted 19 September 2013 - 06:16 PM

I removed the mirror on the exact same scope. Its been awhile. From what I remember, move the focuser to pull the mirror all the way back and insert a stabilizing bolt in the mirror base. Remove the focuser. It just connects to the mirror assembly by slipping a hole in the focuser shaft onto a pin on the assembly. Remove the corrector paying attention to the orientation and any shims. There is a white mark to line up the orientation. Then pull the mirror out. Like I said, it's been awhile but I hope this helps.
David

#6 David D.

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Posted 19 September 2013 - 06:18 PM

Oh. Remove the stabilizer bolt before you try to remove the mirror






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