LX200 Mount

[yuklop]

Hi All,

I have an lx200 classic and the drives are not behaving well. The dec drive has a backlash compensation set to the max (99) and it still isn’t enough and the scope is a picky about slewing to northern areas of the sky, it essentially gets stuck with the drives turning and the scope not moving. 
 

I have taken it apart and have the drives out. I can see two options. Service the drives, there is tons of help online for this, or just keep the worm and main gear and convert it to a onstep system. Both pretty cost effective. 

Do folks here have an idea of the relative pointing and tracking accuracy of the onstep system vs a standard lx200 fork mount drive system?

Remounting on a GEM isn’t going to happen as it is very expensive and also I like the fork mount!!

Many Thanks,

Dan

Edited May 28, 2020 by yuklop
typo's

[michael8554]

Dec Backlash comp flat out isn't normal.

If you take the cover off the side with the Dec motor you will see there's a spring loaded adjustment to the worm mesh, needs to be adjusted to allow the worm to come off the wheel a tiny amount.

Slew to high Dec where you were having problems and check if it's binding or unmeshing.

If there's damage you could unclutch, slew 180 degrees, reclutch, you're now on a probably unused section.

Balancing in Dec with lead fishing weights at the front could help.

Michael

[yuklop]

Hi Michael,

Thank you. I know something is pretty sub-optimal with it. It looked quite odd. Where the spring is between the hinge there is a recessed dip that look like it should seat the spring. In my case the spring was mounted over the screw. I wondered if that was normal too. 
The screw was so lagged in a thick  grey grease that I could barely see it. I would expect that was unusual too. 
But actually the most concerning thing is the play in the little cog on the motor shaft. This may also be hardest to repair.

Dan

 

 

 

[michael8554]

Hi Dan

The shafts in the gearbox have flats onto which the gear lock-screws are tightened.

I imagine some of those screws are easy to get to to tighten, some not:

https://www.thefirmament.nl/astro/main_screen.html?https://www.thefirmament.nl/astro/lx200_dec_play.html&2

NOTE - Imperial Allen keys, not metric.

Michael

[yuklop]

Hi Michael,

Thanks for the link. I think the play on mine is on a different cog, but I suspect the principle of the fix could be the same. I will have a good look and see what I can do.

Regarding the RA drive. Does the picture look right? The is a picture of the drive as it is installed before I removed it. What does that adjustment screw below the spring actually do? I can't see its doing much in this setup, other than being a hard stop if the worm is pushed too far down.

Thanks,

Dan

[michael8554]

The spring is meant to keep the worm on the wormwheel.

The Allen screw should be closer, so that the worm can't jump off the wheel during fast reversals of slew.

About a 1/16th inch free play at the tightest point of the Dec range.

That means, slew the scope between your lowest and highest Dec, looking for where the allen screw gap is smallest.

MichaEL