Help - persistent problems with Nexstar SLT mount skyalign

[Myllymaki]

I've got a Nexstar SLT mount (with Skyalign goto). The goto function used to work quite well (alignment would work on about 4 out of 5 tries, and the goto would then work well). Lately, the alignment procedure works on only about 1 in 4 attempts (using the 3 star align). After alignment, the goto does not work at all. If I ask it to slew to something (like the 1st of the 3 stars I used in alignment), it will literally overshoot the target by about 20 degrees in Az. Its just way off, as if it has no idea how far it has slewed (especially in Az).

I've read a number of posts and have tried a few things (have pulled it apart, put it back together, no broken gear teeth or anything obvious). Has anyone had similar problems with this mount? I'm trying to determine whether it can be fixed or if its just fried and its time to give up on it. Thanks.

[ronin]

This might be a stupid question but the clocks have just changed in the US for Summer Time, in effect DST is now ON when it was OFF some 10 or 12 days ago. Have you accounted for this ?

I know most scopes ask you everytime for DST On/Off but that does not guarantee that all scopes do.

Yours seems to still work from what you describe, I would expect it to simply not work at all so I am guessing that data has changed so if not the above, is there anything else or is it worth performing a complete reset to factory defaults and then re-entering your data fully again.

[matsey]

Hi and welcome to SGL

I would agree with ronin and check your daylight savings settings, that sounds like the most obvious problem - (according to my quick google!) stars move across the sky 15 degrees in the space of an hour, so that would definitely account for everything being roughly 20 degrees out. And again, agree that if you had a hardware problem I'd expect either completely erratic behaviour or for the mount to not work at all - if your handset is confirming that alignment was successful but everything is slightly out, that would seem to imply that something in the data is incorrect - date, time or location.

Other than that, maybe have a go at a two-star align. Not sure how well you know the night sky, but if you can locate and name a couple of bright stars using something like Stellarium or a star atlas, use that method instead and see if you're getting better results. I've got the 6SE which has the same alignment routine, and I've always found the two-star align more accurate than the skyalign, and it will succeed every time (provided you've correctly identified the stars that is - spent 30 minutes once with failed alignment because of that - oops!!). This also might help: http://www.ilanga.com/bestpair/. It's a little piece of software that allows you to pick the best alignment star pairs for greatest alignment accuracy.

Good luck, hopefully it is just a daylight savings issue, but do let us know how you get on.

Matsey

[Myllymaki]

Thanks for the replies. I'll try the two-star align, and if that doesn't help, will reset to factory settings and re-enter my information again. I'm inputting the daylight savings info each time and giving it the correct information, so I doubt that is the cause (also, wouldn't that prevent alignment in the first place vs showing up as goto error after successful alignment, or am I wrong)?

[Myllymaki]

Well, I've confirmed its just broken. Reset to factor settings, did the two star align (polaris, sirius), then told it to goto Jupiter (which it did), told it to go back to Sirius (which it did), told it to go back to Polaris, and it went to Polaris and just kept right on going and stopped about 25 degrees past the target. Told it to go back to Sirius and of course it stopped about 25 degrees short on its way back. Its like it just "slips" internally somehow every few slews and get way, way out of whack. Its a decent manual mount, but the goto is fried.

[matsey]

Hmm not too sure then, would have thought it's a data issue, not sure what else to suggest. Hopefully someone else will come along with some other ideas, particular around the mechanical side which I confess I'm clueless about!

Only other thing I can think of is how you're powering the mount. If by batteries that can cause problems, but even then I'm not sure it would do what you describe. If you can get to some external power source might be worth trying that.

Also... how old is your telescope and did you buy it from new? Might be worth giving the supplier a call for advice - if it's less than two years old it should still be under warranty. Obviously can't say without knowing what the problem is whether it would be covered but it may be worth a phone call at least.

Sent from my iPhone using Tapatalk

[Galilean]

My old 4SE did exactly the same thing - GOTOgot less and less reliable and eventually packed up altogether. And I was always very careful about the correct timing, lat/long etc. Eventually I got rid of it and converted my EQ5 to SynScan - a better solution IMHO.