Maintenance and troubleshooting of a goto dob.

[bomberbaz]

I wasn't sure where to put this but decided here might be a good idea as it gives some perspective to owning one of these to potential new owners.

After owning mine for over two years I started to get some problems,goto accuracy was one http://stargazerslounge.com/topic/256145-goto-accuracy-issue/, slop in the focuser due to heavy ep's another which led to another issue during replacement.

http://stargazerslounge.com/topic/258667-collimating-a-moonlight-focuser/

Another problem with using heavier ep's and pimping the ota up with additional finders etc was clutch slip on the goto system which also needed looking at.

Nearly forgot the handset issue with the manual right slew button sporadically failing to function.

The first issue dealt with was accuracy, I had tried various things including realigning the encoders but for me the thing that fixed it was to simply reset the handset to factory settings, update to the latest firmware and bobs your uncle, or maybe auntie in these modern times! Another point to add here for alignment is to get an illuminated reticle eyepiece and let your star drift into the cross hair, makes a difference but that's my preference and not a must do.

Slop in the focuser was my next concern due to a recent purchase of a heavyweight Nikon eyepiece coupled with a Televue Power mate adding a lot of weight. Prior to this slop had never been a concern but now I was in an all new arena. So a purchased a moonlite focuser and was unsure about collimation of this. To cut this one short my second last post in the thread explains it but here is the copied response:

Simply made sure the secondary was correctly collimated before switching focuser. Then inserted a cheshire into the newly fitted moonlite and checked to see how the mirror looked through this. There was a need to tweak the bottom right hex key and use top right, bottom left to take up the slack to get a even view of white card around it and it was then bob on as they say.

Clutch slip was another problem I saw for the first time after purchasing the Nikon and P/mate. Solved simply by buying some rubber coated weights held in place by 2 earth magnets. I have a 1.5kg one that is on the base of the ota whenever it is in use. When the heavier combinations of ep's / p/mate is used I have a 2.5kg one that can be used in its place.

OK so far, I'll tell you I was shattered by now. Next the manual slew button issue, I first thought that the handset was goosed but it was simply dirty connectors inside. Carefully remove the back cover and seperate the electrical card from the rubber buttons. Now clean the connectors with baader wonder fluid using cotton buds and the problem was fixed. Now reassemble and sorted.

Oh I also cleaned the primary whilst at this and have to say its far easier than I first thought. Additionally I replaced the cheap screws on the primary clamps with high tensile hex bolts.

Finally I collimated the whole scope although it was esentially tweaks on the secondary and full primary alignment.

So as I write this it hard taken two weeks to complete (waited a few days for the hex bolts) but goto is now back to how it should be, the focuser is a dream to use, ota balance is now perfect and collimation is bang on leading to excellent views.

Its been hard work but I am very pleased with the results and its been worth the time spent.

Steve

[Owmuchonomy]

Handy post Steve considering I own the same scope.

[faulksy]

glad you sorted it steve, good result

[Astro Imp]

That's a very timely post as I will be getting the 10" once the holiday season is over.

Thanks for posting.

[knobby]

Great post Steve, you deserve a few clear nights now !

[bomberbaz]

Thanks for the replies chaps especially Chirs and Alan. I hope this does prove useful to you at some point. 

I will just elaborate on some points covered.

The loss of accuracy reason is unknown, it just happened. Maybe a jolt when moving it or just a software glitch nut but as mentioned  the reset cured.

The previous crayford focuser was absolutely fine prior to the heavier weight ep's I bought along with the powermate so might not be a concern to most people. It had previously held some quite chunky eyepieces without problem but add a powermate and the extra lentgh just put a lot of extra stress on it that i wasn't happy with. Hence the replacment.

Also the clutch slip is a new thing as mentioned and again the scope had previously dealt with some quite chunky ep's in the business end. But I think the straw that broke the camels back was me swapping a lightweight RDF for a 60mm scope on a dual mount coupled with a 9x50 finder and this adds a lot of additional weight.

Finally the handset I think still needs an additional clean. I think this time I am going to use some very fine emery paper to clean the connections before giving them a wipe over with the wonder fluid with cotton buds. The amount of muck I got off last time was quite surprising but it still seems to be struggling to get a good connection on the right slew button.

Oh and the bolts I replaced for the mirror clamps were R5 x 45mm and really was a worthwhile thing to do. The screws fitted at the factory are very poor quality and i recommend replacing when you first clean the mirror. I also replaced the screws around both sections on the ota with hex bolts too, a 10 minute, easy to do job.

hth

steve