ETX TECHNICAL TIPS Last updated: 4 June 2006

Subject:	ETX 105 PE RA Tracking Judder
Sent:	Sunday, June 4, 2006 12:46:19
From:	John Kerley (bjohnk@tiscali.co.uk)
I have been using my telescope from new for about 4 months. About a week
ago I started hearing a regular clunking noise when the telescope was
tracking in equatorial mode. Therefore the noise I associated with the
RA motor. (the Clunking obviously occurs in AltAz mode as well). Having
read many articles on your web site I carried out the Reset, Calibrate
Motors and Train Drive. It was when I carried out the Train Drives that
a problem was obvious. The movement in this mode was jerky in both RA
directions when re-centering. This jerky movement was very evident when
viewing the moon which is useless for CCD work and annoying bearing in
mind how new my telescope is.

Rather than have all the hassle taking the scope back to the retail
outlet I decided to see if I could sort the problem. This choice
probably means invalidating the telescope warranty. This could prove a
bad move in the future but its a risk I was prepared to take.

Batteries were removed to safeguard against any accidental electrical
damage. Its not a bad idea to remove the Smartfinder Lens again to
safeguard against accidental damage.

Removing the base involves removing 3 screws which are covered by soft
rubber feet. I tried hard but was unable to remove the feet without
causing obvious damage to them. That's the warranty gone. These feet
were subsequently replace with stick on feet from Maplin (UK). The base
plate was removed and place carefully to one side so as not to damage
the battery wires.

I then checked the security of the 3 screws holding the Central Main
Worm gear housing. All three were loose. All were then tightened. Before
re-assembly I connected an external power supply via the ETX power
socket and placed the scope into its Tracking Mode. Great care needs to
be taken especially when power is applied whilst the inners are exposed.
A short circuit could be disastrous for the telescope. Whilst observing
the clunking noise was still evident. Looking to the right of the Main
Worm Gear (viewed from above with power socket to left) is the Main Gear
Assembly which is within a plastic housing. The clunk coincided with the
far Top Right of this Housing lifting and then dropping. Needless to say
the screw at this location was loose which I tightened down. There were
two other screws holding this housing down which were also tightened.
Beware that one screw is very close to a red wire feeding the electric
motor. I don't know what would happen if this wire was to be shorted but
obviously I wouldn't recommend finding out. Be careful when tightening
screws not to overtighten them particularly the ones around the plastic
Gear Housing which don't seem to bit very well.

The baseplate was replaced, re-screwed and the stick on feet applied.
The good news is that the scope now tracks, as it should, smoothly.
Unfortunately I expect I will need to go through all this again as
vibration will probably cause the screws to loosen again. This really
annoys me as these screws should be locked in place so as not to vibrate
loose. This use to be done by using Shellac / Thread Loctite.(This
Loctite is not Super Glue). I find it pretty poor that Meade do not do
this during the manufacture process of these telescopes. If I do need to
go through this process again I will use such a Loctite compound.

Hope this is useful for others who experience the same problem. It's not
difficult provided care is taken throughout and don't forget the
warranty issues.
 
Cheers,
 
John K
Bristol, UK

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