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Fixing interior cables in mount

Page history last edited by Joshua Pepper 13 years, 2 months ago

Previous users of the Paramount ME have noted a potential problem involving the arrangement of cables inside the mount (see here and here).  The problem is that the two cables of the pass-through signal and power lines that run through the axis of the mount and connect to the instrument panel on the versa-plate are typically tied together inside the mount base with a plastic tie that can be extremely tight.  Because these cables are pulled a little bit each time the mount slews (mostly in right ascension), they rub against each other at the point of the plastic tie, and after a long time they can abrade the insulation and even cut the cables.  See this website for a description and photo of the results.


We were notified of this problem by Rob Siverd at Ohio State who directs the KELT-North telescope.  After a long exchange on the Software Bisque Forums, he diagnosed the problem.  Noting his experience, we decided to fix the problem before deployment of KELT-South.


For our purposes, the solution to the problem is (relatively) simple - remove the cables.  Since we do not use the pass-through signal and power lines to connect camera to the adapter plate on the base of the mount (the USB and power cables to our camera simply hang off the back of the versa-plate), we have no need for the cables.  For those who do use the cables, the solution is nearly as simple: remove the tight plastic tie from the cables and secure them inside the mount in a manner that won't put pressure on them as the mount slews. 


Below, we present the step-by-step process for opening the mount and removing the cables, in a manner that does not damage them.  Although we do not need them for our project, we might at a later date, so this procedure should be reversible.



Note 1: I am using the nomenclature for the Paramount components as listed in the Users' Manual, even if they seem a little misnamed.

Note 2: You will need multiple sizes of allen wrenches for the different sized screws on the mount.  In fact, we found we needed both metric and English/imperial sizes.  You will also need a phillips screwdriver for screwing some very small screws.


The first step is to remove all cameras, counterweights, or other outside equipment from the mount.  Second, make sure both the RA and Dec axes are locked with the worm-gears.  Then, raise the altitude positioning screw (after first loosening the altitude retaining knobs).  Move the mount upwards until the top panels on the sides of the mount are fully clear of the wedge assembly.


Then remove the western side panel (assuming Northern hemisphere orientation).  That involves removing all the allen-type screws around the perimeter of the panel, as well as the 5 small phillips-head screws along the bottom of the panel edge.  You do not need to remove the 4 screws in the center of the panel.  Here is a picture of the removal:



Once the panel is removed, here is a picture of the interior:



The point of interest is the small white plastic tie around the black and gray cables right near the RA axis in the center.


We cut the plastic tie using scissors - NOT the recommended method.  We had no wire cutters at the time, which would probably have been a superior tool.  The problem is the that plastic tie is thick, requiring real pressure to cut, and it is right against the cables, so you have to be careful to cut the tie and not damage the cables.


After cutting the tie off, you can see how much pressure the tie put on the cables after the very short time we have been testing the mount to this point:




There is clear abrasion and even slight cutting into the cable insulation already.


Now disconnect both cables from the circuit board.  That should be easy, but note that the grey cable connects to the board with a clip you have to push to remove.


The next step is to remove the versa-plate and disconnect the cables from the instrument panel.  You can also remove the instrument panel box from the versa plate, since you do not need it.  I will describe the steps we followed, but it might be easier to first remove the instrument plate box before detaching the versa-plate.


Unscrew the versa-plate from the mount.  That involves removing the 4 central large screws and the 8 medium sized screws that are located along one of the inscribed circles.  Make sure to note which circle they are part of so you can put the versa plate back the same way.  Once the versa-plate is off, unscrew the black holding plate under the versa-plate that sits between the instrument panel box and the mount, exposing the cables under the versa-plate.  Unscrew the front of the instrument panel.




Disconnect both cables from the instrument panel.  Then unscrew the instrument panel box from the underside of the versa-plate.



At this point, you can set aside the versa-plate.  The cables will be free on both ends now.  The objective is to pull them through the mount and out the base.





We found that our cables snagged when the ends reached the declination box.  We therefore removed the west panel of the declination box.





We were then able to work both cables out, and the interior of the mount base looked like this.




And that's it.  Replace the versa-plate, and the covers of the declination box and the base, and all done.  One of the fun things to do while the covers are off is to watch the RA motor in action.  In this avi video, you can see it tracking, then slewing, then tracking and slewing again:



RA_motor_in_action.avi (2.7 MB)


I hope this page has been helpful to users of the Paramount ME.  Send us any questions or comments.




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