Fixing LX200 altitude motor issue...

[Sfarndell]

Recently upgraded my scope, but since it is relatively old ('99 LX200 classic), things started to go wrong soon after purchase. Current issue is with the altitude slewing. The motor moves erratically in the slow/medium slew when moving towards the horizon and just vibrates continuously. Opened it up and cannot see the reason (not obvious so has to be electrical).

Any electro-boffins out there with a clue as to what is wrong and how to fix it?

[barkis]

Are you certain it is electrical, does the noise from it change, or is it the just the movement itself that is not uniform. I'm thinking a mechanical problem. Of course a simple bad electrical connection could do it. A rapid make and break connection allied to vibration.

Of course we are in guessing mode here.

Ron.

[David Galvin]

Sound like the infamous dec run away problem which may be a loose connection or, worse, a broken wire.

It can be repaired if you are okay with a multimeter and soldering iron, if not I would suggest that you make enquires with Telescope House as they know what they are doing and are well versed in the service and repair of the LX200. If you are happy to do it yourself then I would suggest that you read the info on this site very carefully, http://members.aol.com/ccdastro/decfix.htm

I cannot take resposibilty for the accuracy of this information.

[barkis]

That's a brilliant link David, and although I am hoping I never get a reason to make use of it, I have the reassurance of it's availability should I ever need it. I hope Sfarndell can solve his problem with it.

Bookmarked.

Cheers.

Ron.

[Sfarndell]

Thanks for the info and links. That is one very useful site.

I will have to read it a few more times before I start playing around with the wiring though.

Regarding the noise, when it skips the noise changes, but not much. The current indicator on the front left of the main board also spikes when there is a skip. To my limited knowledge this may indicate a mechanical glitch - increasing resistance and requiring more current to turn the motor. The skip also happens at regular intervals, but only at low slewing speeds (I haven't been able to test it in tracking mode yet). From limited disassembly, I haven't been able to visually detect anything that would cause this. :scratch:

Keep the ideas coming though.

Scott

[barkis]

If you don't already have it, here is the link to the LX90 site with loads of instructional help.

Ron.

http://m1.aol.com/kewtasheck/lx90.html

[Jeff RV]

Not sure how your powering the scope but i take it it's a good independent supply?

Jeff.

[Sfarndell]

I haven't powered the drive independantly yet. Just trying to gather as much information as possible before I dive in and accidentally destroy the rest of my scope.

Probably won't have time until the weekend to take another look at it, but will keep this post up-to-date with my progress

For anyone else having similar issues, I was also referred to the following site http://astro.lecza.com/Scope/fixes by Alan Sickling, another LX200 fixit guru.

[Jeff RV]

Not sure if the classic has internal supply?, If so Using internal battery's may be part of the problem, you should check this out before proceeding as this is a common problem with the later LXs, it just doesn't leave enough voltage for the scope to run smoothly as well as powering the goto & can be a cause of all sorts of weird things.

Jeff.

[zero]

it's most likely one of the 2 voltage regulators on the dec driver board. They are varialble, so adjusting is relatively easy and done by motor tone and the ammeter on the front panel.

Don't be tempted to power the motor independantly as you stand more chance of knackerring it. The dec on classics is always a little rough so I wouldn't worry about it too much. Run it on 12v not 18 (even though it says 18 on the front panel) and it'll be fine. Also don;t read too much into all the stories and fixes on the net, quite a lot of them are 'sledgehammer to crack a nut'. adjusting your dec should take minutes. One allen key and one screwdriver.

There is a chance that it has gone, and tbh if it has, they are usually not worth the time in stripdown as they don't always survive.

Parts are getting harder to get hold of, as Meade no longer make the spares in the U.S, they only re-condition them. Due to this, and European regulations on lead, Meade U.K can only get complet service kits now, which consist of a motherboard and both motors at £450 (and that's fitted with no labour charge -trade plus vat because they are so expensive). Brian Bond has been known to resurrect lx200 bits -he's a genius, and has done so for BCF for years when supply has been tight.

[Sfarndell]

Reading at how much everyone seems to know about these scopes, I feel somewhat small and ignorant. I am glad, though, as my scope now works!

My problem ended up being the little potentiometer grating being misaligned. The original owner had glued it to the gearbox, so I assumed was it was correctly aligned (why glue something misaligned??). :scratch:

Starting with the recommended basics form the first link, I realigned it visually then closed the gearbox (no screws yet) and turned the scope on. Then I moved the gratings around until the motors stopped running away. A quick test on slow slew mode in both directions to test if there was jerking and presto...job done. Total time: 15 minutes.

Took the scope outside last night and the goto was bang on - even on a 180deg slew from Jupiter to Polaris.

Thank you Ron, David, Jeff and Alan for your expert advice and support. It's nice to know there are chaps like you out there to help guys like me.

[barkis]

The important thing is it's working properly, so now let's hope the sky does it's bit, and allow you some observing time to really test it to the full. Well done, and give yourself some credit, the guys supplied the clues, but you did the job. :salute:

Ron.

[David Galvin]

I am pleased that you have got it working again and I hope it continues that way. I would always take note of what Steve (Zero) has to say as he 'knows stuff ' about telscopes. :salute:

[Jeff RV]

Its nice to see its all tickety-boo at last Scott.

Clear skies.

Jeff.