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Cymrych79
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Reged: 03/18/13

LX200GPS Level North fault new
      #5976737 - 07/17/13 08:09 PM

Hi everyone, I believe this is actually my first post, despite lurking in the corners for a while.

First, a bit about me: Recently purchased an older 8" LX200GPS, which is my first Cass scope, and my first motorized alt-az mount. I still have an old entry-level Meade 114 on an equatorial with Autostar, so I'm familiar with how Meade programs their scopes to move. I've also had a few older non-powered Newts, of various lineages (read: cheap) on both simple EQ and alt-az mounts. I've done about as much as I can with that old 114 and its limitations, and this LX200 is my stepping-up into a more serious role in this fascinating hobby.

Not sure how old this LX200 really is. Due to Meade's nonsensical serial numbers, I've no way to really figure it out. I suspect its an early run of the GPS line, since the handbox had version 1.2b of Autostar II when I got the scope. I've updated it to 4.2g prior to taking it out in the field for the first time.

So, I got my new 8" on the 4th of July, and as usual for a new scope, either weather or work keep me from getting First Light until last night. The sky was clear, but transparency stank (very VERY humid, with moderate-to-bad skyglow) and since I'm on the road for work and don't know the local haunts, my viewing location was very much less than ideally dark. What I could see, say, +30 degrees above horizon was good; I like the optics and the much improved field of view over my old 114, and what stars I could see were nice and sharp ... they were only limited to lower mag 6s, unfortunately.

The one glaring issue I had was with any Auto alignment I attempted. From a loosely set Home position by hand, I turned on the scope and selected Auto Align to start. The scope made a slight slew to north just fine, then tried to find level ... and failed. The ota just rotated straight up to vertical, and gave me the Level North Error message. Double checked my tripod's level was true, tried it again. Same result. Tried the Easy alignment, paying much more careful attention to my maunally set Home position: same error message. Eventually, I used a 2-star manual alignment, which worked fine. Once I confirmed that alignment was indeed possible one way or the other (ie: that I remembered how to do it from my 114 days), I attempted to do a calibrate sensors routine. Failed again on the detect level step.

In the end, I just stuck with the manual 2-star alignment, and went about my evening viewing. Despite the incessant mosquitos, air so humid you could cut it with a knife, and the ever-present glow from the baseball field's security light, I still say it was a qualified successful First Light!

Now then, back to the finding level error ... any thoughts? The scope slewed accurately to north every time, and the GPS always successfully got a fix (verified, sort of, by examining the time in the Setup menu). I don't rightly know, but it seems that the Tilt and Tip position measurements must be based on the scope actually finding level, so obviously, they failed as well.

I've severe concerns about sending this scope to Meade at the moment for servicing, given their current troubles, and at any rate, it's way out of warranty and I ain't about to shell out cash for something I can likely fix myself, so long as its hardware related. To that end, I've no fear about popping a cover and examining the innards ... just need some guidance about what to look for and what to check!

Thanks for your patience reading this long post.

-Jason

Edited by Cymrych79 (07/17/13 08:30 PM)


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Cymrych79
member


Reged: 03/18/13

Re: LX200GPS Level North fault new [Re: Cymrych79]
      #5976747 - 07/17/13 08:15 PM

I should have mentioned that I don't know if the Level North Error existed prior to updating Autostar II to 4.2g. When I picked up the scope, the seller already had it up and running, so I didn't see his alignment technique (and never even gave it a thought, frankly). Updating to 4.2 just seemed like the logical thing to do while I waited for the weather to cooperate enough for me to get it outside. To the best of my knowledge, all the options in the menus were properly set (yes, including the Use Sensors bits as well) menu by menu and item by item by me after updating the firmware.

Also, if it turns out that fixing/replacing this sensor is more of a hassle/expense than its worth right now, that is fine. I don't mind a manual alignment process (they're kind of fun, actually). But it seems as if the level of the base becomes a hugely important factor for precision manual alt-az alignment, and I don't know if any precision adjustments exist, akin to the drift tests for precisely zeroing in RA and Dec on an equatorial. Any advice here would be appreciated as well (if for nothing else than the knowledge of how to get the precision I usually strive for)!

-Jason

Edited by Cymrych79 (07/17/13 08:25 PM)


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jrcrillyAdministrator
Refractor wienie no more
*****

Reged: 04/30/03

Loc: NE Ohio
Re: LX200GPS Level North fault new [Re: Cymrych79]
      #5976778 - 07/17/13 08:28 PM

Celestron's contemporary Nexstar GPS models used a ball-in-track level switch and it wasn't unheard of for the ball to get stuck. Rotating the tube through level a few times would clear it.

I don't remember what the Meade level switch looks like but I think I remember that one could hear it click. If you release the clutch and rotate the tube in elevation you should hear it. If you hear it but the mount doesn't see it then there's an electronics problem. If you don't hear it then the switch could be stuck and you might be able to free it.


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Cymrych79
member


Reged: 03/18/13

Re: LX200GPS Level North fault new [Re: jrcrilly]
      #5976802 - 07/17/13 08:46 PM

There is indeed a nice little click of what sounds like a bearing in a track as I rotate the ota through level. Setting up an experiment now, from a clearly nose-low attitude, to see conclusively indoors in the light if the scope will pass through level without stopping.

I imagine there must be contacts of some sort at the limits of the track, which might be corroded or dirty?

EDIT: Test failed at finding level, after clearly hearing the bearing shift in the track while scope slewed. So, obviously, the sensor isn't reading the position of the bearing in its track.

Edited by Cymrych79 (07/17/13 09:01 PM)


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Cymrych79
member


Reged: 03/18/13

Re: LX200GPS Level North fault new [Re: Cymrych79]
      #5976885 - 07/17/13 09:58 PM

Hmmm, doing some more research, and there seems to be some suggestion that Calibrate Sensor remembers the north and level off-sets and applies them to ALL future alignments (of course. What else would a calibrate function do?). I seem to recall aborting a Calibrate sensors after updating my firmware. I wonder if I inadvertently "told" the application that level was in some utterly wrong position, and the scope is attempting to find this misplaced "level"?

Perhaps an Autostar Reset is in order ... start from square one, and see what happens.


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P26
Vendor - Peterson Engineering


Reged: 05/02/12

Loc: RI, USA
Re: LX200GPS Level North fault new [Re: Cymrych79]
      #5977652 - 07/18/13 10:45 AM

You may have a loose cable in either fork arm. And a number of scopes have failed when a wire in the cable running in the GPS arm breaks due to continued flexing.

First I suggest disconnecting and reconnecting both ends of the cable runs in both fork arms. If that doesn't work run a continuity test on that flexing cable.

Clear skies,

Pete Peterson


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Cymrych79
member


Reged: 03/18/13

Re: LX200GPS Level North fault new [Re: P26]
      #5978208 - 07/18/13 04:00 PM

Well, checked in both fork arms. Glad to report no obvious circuit board failures or poor connections. All wiring was nice and snuggly connected and clean. Checked the gears, since I was in there, and likewise see no tell-tale signs of unusual or uneven wear, and the grease is still clean and without any metalic grit.

On the left side, I did have to pop a zip tie on the level sensor ribbon as it wraps around the declination axis, mostly to example a rather folded and crimped section of the ribbon. Again, everything looks ok. Have to find my electrical tester to confirm continuity still.

One issue I did find was on the sensor board itself, specifically, the forward-most of the two chrome set screws used to attach the board to the top of the ball-track plastic box screws into a cracked housing. As a result, the board has some flex to it, and doesn't sit solidly on the ball sensor. I'm waiting for the glue to set now.

Is there a preferred or better way to route the sensor ribbon? It just seems like no matter how I try to arrange it, there's a good deal of flex on the ribbon every rotation in dec.

Thanks all,

Jason

Edited by Cymrych79 (07/18/13 04:04 PM)


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Cymrych79
member


Reged: 03/18/13

Re: LX200GPS Level North fault new [Re: Cymrych79]
      #5978594 - 07/18/13 07:59 PM

UPDATE:

Yep, turned out I did have a discontinuity in the ribbon cable, on one strand of the 7. Sure enough, there was a slight break in the plastic coating right at the break too. Didn't have much luck finding a computer shop with spare ribbon, so fannagled a quickie soldering job on the broken strand, waited for the glue on the busted bearing screw-hole to cure, and plugged it all together.

Turned on the scope, a selected a Calibrate Sensors function, and success! The scope found level on all its various dips and bobs, and if I listened closely, as soon as I could hear the bearing the motor would stop. So, it seems as if everything is doing what it should (although, I was inside, so the GPS fix failed, and when it attempted to turn to Polaris, the scope ran the wrong way. A full test will have to wait until I get the time to get it outside.)

Anyhow, the electrical break in the ribbon was the culprit. My fix seems to have worked, but frankly, I don't particularly trust my soldering! But this buys me time until I can locate some new ribbon, and perhaps a new sensor (or at least the plastic bearing part of the sensor) from Meade.

Thanks for everyone's help!

Blue skies

Jason


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P26
Vendor - Peterson Engineering


Reged: 05/02/12

Loc: RI, USA
Re: LX200GPS Level North fault new [Re: Cymrych79]
      #5979587 - 07/19/13 10:45 AM

Hi Jason,

It's best to ask Meade for a replacement ribbon cable. This is a frequent failure mode and they should be used to accommodating it.

As for the ribbon cable run, observe the cable while moving the OTA up and down to see exactly where and how it flexes. Many many scopes ship with the cable run set so that the cable flexes at one point in a very sharp bend. Rearrange the cable so that the bend has a maximum radius, preferably with almost the entire length of ribbon cable bending at the same time in a large arc.

I also doubt that your solder job will hold, given the flexing. Either go for a new cable from Meade or make up a new one utilizing the existing end connectors and some ultra fine stranded wire.

Clear skies,

Pete Peterson


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Qwickdraw
Pooh-Bah
*****

Reged: 03/03/12

Loc: Ann Arbor, MI
Re: LX200GPS Level North fault [Re: Cymrych79]
      #5980373 - 07/19/13 07:06 PM

Quote:

Well, checked in both fork arms. Glad to report no obvious circuit board failures or poor connections.
Jason




As a former Electronics repair tech I can assure you that you would want to find a loose connection.


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Cymrych79
member


Reged: 03/18/13

Re: LX200GPS Level North fault new [Re: P26]
      #5986508 - 07/23/13 05:38 PM

Quote:

Rearrange the cable so that the bend has a maximum radius, preferably with almost the entire length of ribbon cable bending at the same time in a large arc.

I also doubt that your solder job will hold, given the flexing.




Hi Pete,

Yeah, the way it was routed (presumably by the manufacturer), almost all the flex was isolated at 2 locations on the ribbon, where the wire was already bent most sharply. After my temporary soldering job and re-routing, the flex is spread out over much more of the whole length of the ribbon. I don't know, that seems to make more sense to me!

As for my soldering, I don't anticipate it lasting terribly long either, despite stiffening up the particular area with heavy tape. Mainly, it's just a band-aid until I get ahold of Meade. I can't imagine that a ribbon would cost too much.

Thanks again!

Jason


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Cymrych79
member


Reged: 03/18/13

Re: LX200GPS Level North fault new [Re: Qwickdraw]
      #5986517 - 07/23/13 05:42 PM

Quote:

Quote:

Well, checked in both fork arms. Glad to report no obvious circuit board failures or poor connections.
Jason




As a former Electronics repair tech I can assure you that you would want to find a loose connection.




Indeed. Built enough computers over the years to know what can happen with a shoddy contact. Worst case scenario: What's that burning, ozone-like smell??


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