5 replies to this topic

[swagner272]

Celestron CPC 800 XLT with Nexstar* HC

 

I can do a Skyalign, Two star, or solar alignment with no issue and a "success" message.  Once aligned however, the telescope immediately begins to slew ignoring any slew limits. It will occasionally stop for a few seconds and then begin slewing again.  There is no way to stop it without tuning off the telescope. UNDO does nothing, selecting another object may change the direction but the telescope will not go to the object or stop at any point. 

 

Some more background - I just bought the telescope used (amazing deal). It had the original firmware and the GPS issues associated with it.  I was able to update both the MC and HC firmware and the motors do seem smoother. I purchased a new AC Celestron power cord to confirm I was not having power related problems.

 

I have gotten it to successfully align and allow goto and track correctly only twice.  I cannot figure out what i did differently at those times. Once was during the day using solar align to the moon right after the firmware updates and the other a two star alignment that netted a great dumbell nebula shot and poor M31 shot before dew shut me down before the updates manually entering location and time.

 

This has been frustrating as setting everything up involves a little planning and after 4 or 5 nights not being able to use GoTo or track objects I am getting discouraged.  

 

Any advice?  I cannot seem to find any similar problem or solution.

Thanks in advance for any input.

Edited by swagner272, 11 August 2022 - 10:33 PM.

[mclewis1]

Does it run away in one axis or both? Does pressing any one of the direction arrows stop the runaway? Have you done a Factory Settings reset of the hand controller?

 

It could simply be cabling/connectivity issue, like an intermittent connection. I'd carefully unplug/plug the connections to and from the MC board and take a very close look at the connector on the motors, in particular the small connections to the encoder wheel. I'd also take a very close look at both encoders, looking for a loose or scratched disk.

 

To test the scope out I'd do some GET/Goto axis position moves back and forth and watch the Get axis position numbers ... they shouldn't drift or suddenly change to something different, they should just change between with the two positions you're slewing back and forth between. Random drift or sudden changes in these numbers might indicate an encoder problem on one of the axis (my best guess at your likely problem).

 

If I'm right you'll need to either carefully fix a loose encoder disk (there have been a number of threads on CN about doing this for a variety of Celestron GEM style mounts) or replace the encoder/motor assembly for that axis.

Edited by mclewis1, 12 August 2022 - 10:28 AM.

[Cristofori]

Celestron CPC 800 XLT with Nexstar* HC

 

I can do a Skyalign, Two star, or solar alignment with no issue and a "success" message.  Once aligned however, the telescope immediately begins to slew ignoring any slew limits. It will occasionally stop for a few seconds and then begin slewing again.  There is no way to stop it without tuning off the telescope. UNDO does nothing, selecting another object may change the direction but the telescope will not go to the object or stop at any point. 

 

Some more background - I just bought the telescope used (amazing deal). It had the original firmware and the GPS issues associated with it.  I was able to update both the MC and HC firmware and the motors do seem smoother. I purchased a new AC Celestron power cord to confirm I was not having power related problems.

 

I have gotten it to successfully align and allow goto and track correctly only twice.  I cannot figure out what i did differently at those times. Once was during the day using solar align to the moon right after the firmware updates and the other a two star alignment that netted a great dumbell nebula shot and poor M31 shot before dew shut me down before the updates manually entering location and time.

 

This has been frustrating as setting everything up involves a little planning and after 4 or 5 nights not being able to use GoTo or track objects I am getting discouraged.  

 

Any advice?  I cannot seem to find any similar problem or solution.

Thanks in advance for any input.

I think Mark is on the right track. I had a similar problem with a CPC1100, which was a power connectivity issue. If the power connector is the same on the CPC800, the pin in the connector on the mount is not a solid pin and can be spread apart using a micro screwdriver. After spreading my CPC100 connector, it fits more snugly with the power adapter and has eliminated the random slewing problem. I hope this simple tip fixes your problem!
 

[swagner272]

I will have to go shopping as I do not have the correct sized allen wrenches to get the case apart and the clutch knobs off.

 

It is only moving in one direction on the ALT axis.  It even appears to go to the correct AZ when putting in an object.  Given what I know so far, it seems the MC board or a connector is likely the issue.  I'll let you all know when I get the thing apart. Probably not for a few days.

[mclewis1]

If it is a fairly solid problem with no motion in one direction on the AZ axis then first try swapping the AZ and ALT motor connections going into the MC board. You won't be able to perform an initial alignment but the resulting behavior will tell you a lot.

 

If the AZ axis continues to only move in one direction then the problem lies in the cable or the motor/encoder assembly.

If the problem moves to the ALT axis then the problem is with the MC board.

[swagner272]

OK-- I got it all taken apart-- most instructions I have found leave out the screw under the Celestron logo on the base cover.  I reseated all connections multiple times. No luck.

 

It is not that I can only get it move in one direction - it just constantly moves in that direction.  After further diagnosis, I have come to realize the Telescope is not getting an ALT reading. I assume that because of this, as soon as it tries to track or slew to anything it revs up the ALT motor in an attempt to get it to the correct coordinates. As it thinks it is at 00.00.00, it keeps the motor going.

 

At this point it is surely either the decoder/motor or the motor control board. I am not sure which.  To figure that out, I know I need to switch the ALT and AZM connections on the main board and see if the problem sticks with the ALT motor or switches.  The motor is about $130 and the Board about $160.

 

Is there any other reason the HC would not be getting the ALT signal?  I also tried using NexRemote on a PC and it gets no alt signal as well.  Both can manually slew the motors in all directions.

Edited by swagner272, 13 August 2022 - 01:28 PM.