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Last updated: 8 January 2012

Sent:	Wednesday, January 4, 2012 19:48:47
From:	Russell Colina (
I was observing with my ETX-90 EC recently when it suddenly failed to
respond in altitude, Autostar ominously reported a motor
fault...Switching hand controllers from my Autostar to the stock
controller failed to resolve the problem.

The telescope firmly refused to respond to any key inputs in altitude,
azimuth function worked perfectly.

I removed the base and the problem was revealed, to my horror the yellow
wire feeding through the centre gear of the telescope was neatly chopped
through by the gears in two places!

I replaced the section of lead with wire from computer ribbon cable
which proved to be of similar gauge/size. This I carefully soldered in
and insulated with a length of heat shrink tubing.

I tentatively re-connected my Autostar fearing the worst for the
electronics, however all was well and the telescope functioned again as

However the fear of this re-occurring lead me to find some way to
prevent this happening again. I cut a protective guard from the plastic
cover of a clear file binder as this seemed to be sturdy but not too
bulky. Two holes were cut to allow passage of the wiring and to also fit
around one of the telescope base pillars. Size of the guard is not
critical, just sufficient to prevent the wires from getting caught in
the gears.

The following steps may be helpful;
(1) Remove the batteries.
(2) Peel off the three rubber feet, the screws securing the base are
hidden underneath.
(3) Remove the three phillips head screws now exposed.
(4) Carefully lift the base watching that the wires to the battery
compartment are not overly strained.
(5) I desoldered the power leads from the battery base to prevent any
problems arising from the leads being inadvertently broken away from the
control panel. Ensure you mark the polarity!
(6) Note the position of the wiring within the scope base, a photo is
helpful for reassembly.
(7) Check & repair any damaged wiring in the vicinity of the central
gear, also ensure the insulated sleeve through the centre shaft does not
protrude too far out.
(8) Make and install the protective guard as per the photo's.
(9) Check the connectors on the back of the HBX/AUX/switch panel are
fitted securely and ensure the wires are routed correctly.
(10) Resolder the power leads observing correct polarity. Reassemble the
base to the 'scope  and reapply the rubber feet. Refit the batteries,
again observing polarity.

The photo's enclosed are hopefully clear enough to give the general idea
and, as they say, a picture is worth a thousand words!
I am unsure how much of an issue this is with ETX's, however "an ounce
of prevention is worth a pound of cure" as they say.

The modification has resolved the issue of wiring entanglement in the
gear drive and I would encourage ETX 90 owners to carry out this simple
mod before the wires get cut in the gear teeth, I perhaps was lucky that
no damage was done to the electronics.

Hoping this will prove useful to all ETX owners,

Russell Colina
New Zealand.



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