Re: AP900 Dec backlash - more help required

John Winfield

Hi all,

Thanks to the guidance here, I've removed the motor box cover and
inspected the gear train underneath.

I've discovered that when driving the Dec motor at 1x sidereal speed,
it 'jumps', once or twice per revolution.
This seems to predominantly happen after changing direction - if I
keep running in the same direction the jumps seem to stop after a few
I'm guessing this is indeed due to a loose locking screw on one of the

I put a pencil mark on the end of the motor shaft and after a few
jumps it still seemed to be in the same orientation wrt to the locking
grub screw, so I'm assuming it's not that one.

I can't get to the locking screw on the motor shaft through this side
cover to check it's tightness and can't even see the locking screws on
the other gear shafts.

Am I on the right lines - and are there any guidelines on how best to
adjust the locking screws on these other hard-to-reach gear shafts?

I'm not a mechanical whizz, but I'm reasonably competent.



--- In ap-gto@..., chris1011@... wrote:

In a message dated 4/23/2007 2:08:04 PM Central Daylight Time,
winfij@... writes:

Thanks for clarifying that - this is a circa 2003 mount, purchased
used as you say.
In a lot of cases, when a mount has been purchased used, the person
who ships
it will not package it correctly, and the result is that stress is
put on the
motor box/worm gear. This then results in poor worm mesh, so the
first thing
a new user must do when he/she recaives a used mount is to do a
re-mesh on
both axes. Probably the biggest mistake is to take such a mount out
of the box,
set it up outside and expect it to work perfectly. It probably will
not work
quite right until the gear mesh has been checked. Also, many times a
mount can
have other minor things out of adjustment which the previous owner
realized, but which the new owner will see right away. Therefore do
not hesitate to
check all things in the daylight before trying it out in the dark.

Are there any instructions/pictures as to how to remove the motor box
cover, just to make sure I get the correct screws?
The motor box cover is located on the opposite end of the worm shaft
Remove the 6 small Allen head screws and the cover will slip off.
You will then
see the spur reduction gears. Once you see them, you will understand
how it
all works.


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