8 replies to this topic

[E Sully]

Just thought I would mention something I read on another forum.  Seems as though a new owner was concerned over the accuracy of LX90 ACF.  He changed the gear ratio and accuracy improved.  Another member questioned him about the need to change the ratio.  Eventually, the Dec gear cover was removed, and gear teeth counted. 

It seems an LX90 should have a 154 tooth gear, but somehow this one had a 156 tooth gear installed.  Meade did replace the scope with a new one, and the owner is now thrilled with his scopes accuracy.  It may have been a very rare one of a kind issue, but if you have a poorly performing LX90, It does not take a lot to remove the declination cover and check your tooth count.

 

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[MistrBadgr]

Thanks, Ed!  I read that same account, but did not think to post about it here, since I am concentrating on work with Infinity 60 scopes right now.

 

Bill

[RickScofield]

Thank you that is worth checking.

[Piet Le Roux]

I am the lucky one with the 156 tooth gear and to be fair Andrew Johansen  took my calculated ratio (2.78686) and looked at all the mathematical possibilities and came to the conclusion that the only thing that made sense is that my LX90 was fitted with a 156 instead of a 154 tooth gear but did not think its possibly. I then counted the teeth and confirmed this! But it was a very interesting investigation and all ended well. He then calculated the ratio using the right formula and came to 2.78646875. The scope is still perfectly usable as long as it has this ratio.             

[Piet Le Roux]

It is possible to check if your scope has a faulty gear or a problem with its optical encoder without opening anything and voiding your warranty. It is called a spin test, I call it a 360 degree tracking test. You can use the same terrestrial object that you use to train your drives with or, if you have a bubble level on your OTA, you can do this simple test completely indoors. The object is to compere your scopes electronic angle measurement to the angle that which it has actually travelled. For the  Alt axial (horizontal) you could use the RA scale on the base of your scope. Set the scope up as for home position and zero the RA scale. Switch the scope on and keep on pressing "mode" until it displays "select Item: Object". Press the "mode" key for 4 seconds and it would display your RA and Dec values, press the bottom right down key and it would display your Alt and Az values which should  be all "0".  You can now press the left or right arrow but like the "Train drive" procedure you can only travel in one direction. The moment you over shoot the accuracy of the test is compromised. Rotate the scope for 360 degrees until it reaches the "0" mark again, near the end select a slow slew rate to make it easier. If it has rotated exactly 360 degrees check your Az reading on your handset : if it is on 0/360 degrees you don't have a problem, if you have a 156 tooth gear it would display about 4.65 degrees too much because the drive had to do more revolutions that it anticipated to complete 360 degrees. If you have a dirty encoder disk it would read about 3.3 degrees too little for every vein of the encoder it cannot read, so it would indicate less than 360 degrees.      

[MistrBadgr]

If the encoder is dirty, would you read less than a 360 degree travel?

[RickScofield]

Can anyone provide a link to this story on the other forum or navigation?
Thank you , Rick

[E Sully]

Here is a link to the LX90 gear issue.

http://www.astronomy...r-accurate.html

[RickScofield]

Thank you Sir.