Last updated: 12 May 2004

Cleaning the Encoders

Sent:	Saturday, May 8, 2004 22:27:35
From:	"Ignacio Perez-Puelles" (
Thank you for this great site, I've been checking it out regularly
before I even bought my own little Mighty ETX.

I've had the ETX-125ec UHTC for a year now, and I'm very happy with it,
it is a very fine optical instrument and also very portable.

Although some mechanical glitches have been bugging me occasionally:
Motor Unit Fault, rubber banding and poor goto's.

But still a good deal when I bought it back then, it included the autostar
#497 & tripod #884 for free, & the eyepiece kit for $99.Also got the
Electric Focuser #1247 (preety nice, a bit expensive), Barlow lens #126
(I don't like it, low quality), and a Series 4000 neutral density "moon"
filter (nice too).

Thanks to your site I was able to build my own #505 cable to hook up
with the Laptop and download updates for the autostar, and control the
telescope using Starry Night Pro software and ASCOM drivers for Windows.
(that is so great!!!). Also to use an external 12v. rechargeable battery
instead of the 8 double AA's. (saves money, lasts longer!!!).

Ok. now on to how I solved my problem with the Motor Unit Fault:

As mentioned on your site, this could happen for a number of reasons:
low batteries, calibrate & retrain, overload, etc. I tried with new AA's
batteries, also had second thoughts on the external 12v. rechargeable
battery, tried many calibrate & retrains.Nothing. Unfortunately for me
it was the greasy mess on the motors that caused the problem, I really
would have not thought of taking the telescope apart, it being a precise
instrument and all..., but thanks to your site, again !!!, this became
an easy yet careful process.

To clean the Declination Motor, remove the OTA, and covers from the right
fork arm, (details on this procedure are found on mike's website). The
excess grease can be wiped off, and the most important part is the
ENCODER, this has to be cleaned very well, mine was a complete mess
covered with grease. I removed the motor assembly and all the gears
completely from the arm and cleaned everything thoroughly, then greased
lightly again the gears only.

To clean de Right Ascension Motor, remove the bottom cover of the
telescope, be careful with the battery compartment cables, again here I
removed the motor assembly and all the gears completely from the base and
cleaned everything thoroughly, then greased lightly again the gears
only. the encoder here was also completely covered with grease. The Right
Ascension's clutch has to be loosened a bit to be able to remove the
motor assembly and the gears, but be very careful with the set of wires
that run up through the middle they may get stripped.

Now this baby purrs like a kitten and it doesn't stop !
I've let it run all night long tracking objects !
Motor Unit Fault - you are history !

Thank you Mike, and all the other people who have contributed to this site, the amount of info available is amazing.

I've attached a couple of pictures below:

Now, the rubber banding and the poor goto's... Well, I've tried the calibrate & train drives many times, but I'm not sure it's working right. Is there something I'm missing here ? There are some options in the Autostar setup menu that I do not understand, I'll list them below for you to check out... I'm using Autostar version 31Ee SETUP: TELESCOPE: Az/RA Ratio: +01.36889 Alt/Dec Ratio: +01.36889 Az/RA Percent: 50% Alt/Dec Percent: 50% Tracking Rate: Sidereal Max. Elevation: 90 Min. AOS: 5 I don't know what these values are for, please give me a hand here. Hope to hear from you soon, bye. My name is: Ignacio Perez-Puelles. Thank you.
Mike here: Check out the article "Calibration, Training, Percentages" on the Autostar Info page. I think that should answer many of your questions. Sidereal means the Autostar uses the same rate as the Earth's rotational rate to compensate for the Earth's rotation. AOS is the minimum altitude for satellite acquisition tracking.

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