Fix the SW120ed, dewshield off

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Jones
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Fix the SW120ed, dewshield off

#1

Post by Jones »

Bought a used 120ed a few months ago and visually it was awful. Barely better than an achromat. Lots of blue one side of focus, lots of red on the other side of focus. But the colors were bleeding into the focus point and smearing the image of Jupiter. Had to open the lenses and see what was wrong inside. First problem was getting the dewshield off. Here are the tools you will need.
20200724_102153.jpg
To get the dewshield to unscrew will need a hair dryer and 2 strap wrenches. The wrenches should have all plastic handles and rubber straps. No metal to mar surface of telescope.
Arizona- where the sky's are not cloudy all night.
Jones
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Posts: 111
Joined: Tue Jun 23, 2020 12:21 am
Location: Arizona

Re: Fix the SW120ed, dewshield off

#2

Post by Jones »

20200724_110707.jpg
You want to heat the base of the dewshield 3-4 minutes, try not to heat the lens cell.

Position the strap wrenches as in photos while the dew shield is hot. You want the teeth to press down on the rubber strap in the direction of rotation. One wrench on the lens cell to hold telescope steady. Dewshield wrench to attempt to unscrew.
20200724_111038.jpg
20200724_111049.jpg
It took me 3 heating attempts to get dewshield to unscrew. Extreme pressure was required to break free. Position the telescope so it can not fall if you lose control of the strap wrenches when they slip. I left the rings and mount bar on the tube to prevent it from rotating. It might work better with the lens assembly off the tube so as not to jar the focuser shaft. You have to be very careful that the lens assembly does not get away from you if/when a strap slips.
Arizona- where the sky's are not cloudy all night.
Jones
Mars Ambassador
Articles: 0
Posts: 111
Joined: Tue Jun 23, 2020 12:21 am
Location: Arizona

Re: Fix the SW120ed, dewshield off

#3

Post by Jones »

20200724_124616.jpg
With the dewshield off you can see why it would not come loose- the threads are absolutely dry. The lens assembly to tube threads are flooded with grease, why they did not lube the dewshield threads, who knows. To keep the dewshield from ever locking up again, put a drop of oil on a small brush and 'paint' the threads with the lubricant.
Arizona- where the sky's are not cloudy all night.
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