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DEC Motor for Meade LX-850

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15 replies to this topic

#1 wdhensley

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Posted 16 March 2024 - 06:55 PM

My DEC motor on my LX-850 has frozen up.  I know this because I took the covers off the drive housing and I can not turn the gears by hand.  When I took the top cover off, ther is a thin white power inside the housing so I think it burnt up.  Where might I purchase a new motor to install in my mount?

 

Thank you,

 

Wayne Hensley

(313) 407-2288


Edited by wdhensley, 16 March 2024 - 06:57 PM.


#2 OzAndrewJ

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Posted 16 March 2024 - 08:33 PM

Gday Wayne

My guess is you will need to ring Meade

as i have never heard of an LX850 motor needing replacement.

Also, I havent heard of anyone who has fully removed the motors from an LX800/50

but i know they are a different "setup" to the LX200s etc as

The LX200s have an integrated 50:1 gearbox and 256 line US digital encoder

The LX800s have a 36:1 external gearset and 500 line AVAGO encoder.

The LX200 "motors" are specially wound for Meade by Igarashi

but based on the different configuration, and the fact the LX850 doesnt have

a gearbox, i would be suspicious of the motors axle dia.

If it is really burnt, maybe remove it and take some piccies :-)

 

Andrew Johansen Melbourne Australia



#3 AF7JQ

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Posted 16 March 2024 - 10:04 PM

You might also contact this guy...he works on LX850 scopes.

 

https://www.meademods.com/

 

John



#4 wdhensley

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Posted 17 March 2024 - 06:00 AM

Gday Wayne

My guess is you will need to ring Meade

as i have never heard of an LX850 motor needing replacement.

Also, I havent heard of anyone who has fully removed the motors from an LX800/50

but i know they are a different "setup" to the LX200s etc as

The LX200s have an integrated 50:1 gearbox and 256 line US digital encoder

The LX800s have a 36:1 external gearset and 500 line AVAGO encoder.

The LX200 "motors" are specially wound for Meade by Igarashi

but based on the different configuration, and the fact the LX850 doesnt have

a gearbox, i would be suspicious of the motors axle dia.

If it is really burnt, maybe remove it and take some piccies :-)

 

Andrew Johansen Melbourne Australia

Thanks Andrew ... I have also sent an email to Meade.  I am going to remove the motor today and I will post some pics.

 

Wayne



#5 wdhensley

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Posted 17 March 2024 - 06:01 AM

You might also contact this guy...he works on LX850 scopes.

 

https://www.meademods.com/

 

John

Thanks John ... I sent him an email as well.  Thanks for the info though!

 

Wayne



#6 wdhensley

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Posted 17 March 2024 - 08:36 AM

Here are some photos of the Drive assembly and motor.  AS mentioned in my earlier post, I can't turn the motor by hand.  I see that it is made by Maxon ... I went to their site and searched for the number number shown on the motor (397077) but nothing came up.  I see there is a Meade dealer in the UK (https://www.meadeuk....r-Assembly.html) that has the entire assembly.  I have sent an email inquiring about the availability.  The price around $750.00 US.  Seems very high but I would rather spend that amount than to have to replace my LX-850 mount because of a $125.00 (?) motor. 

 

in Image 1379, there is a white substance on the housing ... not sure what it is.  There is also an odor, not the smell of a burnt resistor, that would indicate something something burnt.  In image 1382, I assume the black housing on the back of the motor is an encoder ... the odor is strong around it.  I am unable to remove the cover to view inside so I may need that item as well.  Anxious to see replies to this post.

 

Wayne

 

 

 


 

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#7 MikeBY

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Posted 17 March 2024 - 02:25 PM

Hi Wayne,

I'm surprised to hear of an event like this with a LX850. Not to say motors don't fail, but it's FAR more often motor driver chips, encoders and interconnections that cause issues. 

1st off, 

Andrew is as good as it gets on Meade gear.

Meademods is relatively close geographically and that's good news if you need direct assistance, and of course there's Meade support. Hope you will hear soon.  Meade might be able to supply specific tech data if you ask the right questions on motor windings resistance,  etc. I haven't interacted with them lately.  

 

Thinking about what I might add to the discussion, and few things I'd suggest checking at this point.

Your nose smelt an overheating.  But the important unanswered question is not only WHAT but also WHY.

* is the motor actually frozen now that you've got it out? 

* check and record motor windings resistance, opens, shorts. 

* check windings for shorts to motor frame/case.

 

At this point you'd be looking to see if the windings are intact, have actually burnt out or a short exists, but the actual readings might be a useful reference for future use. 

 

The motor driver board status is a big ?? in my mind, especially if it's pushed enough current to burn or overheat a motor winding and in fact could be the root cause of a damaged motor. 

 

* Have you reconnected the motor since removal to see if the driver will move it during scope initialization ? 

 

If the DEC axis motion was frozen in a power off condition and is now free with the motor removed I would speculate that the LX850 motor has integral gear reduction and that's where the failure occurred. It might not be immediately apparent under no load stand alone testing. I'd give it a try as it might be illuminating. 

 

What was the status of the OTA and associated optical gear at the time of failure?  

What was the DEC balance like?  Nose or mirror heavy?  Position? In retrospect were there any prior symptoms?

 

Before ordering and putting expensive and hard to obtain replacement parts in place,  it's important to understand everything we can about what failed, how it failed. and to the extent possible what caused the failure. So too, also inspect and test as many of the involved component parts as we can in the process both to rule out root causes and to identify any collateral damages.

 

I'd be hesitant to wholesale replace the entire DEC assembly. Seems to me that a very expensive sledgehammer is the wrong tool at this point. I would not contemplate anything as drastic, as you put it,  a mount replacement due to the cost of a motor. 

 

Just as a point of reference and context for myself and others, as I haven't seen or heard much about LX850 hardware issues, and if you don't mind sharing, might I ask:

How old is the scope? Can you estimate how much operational time is on it? It's sufficient to say even in broad category; ie. occasionally, X times/month, weekly, daily. 

Is it permanently mounted (observatory,etc) or portable use. If portable, is it set up and taken down each time or left set up on a tripod with wheels, etc.  

I'm just trying to get an idea of circumstances in general to gain better insights and a knowledge record from your unfortunate incident and situation.

There is a great community here, ready and willing to help you work through this best we can. Every bit of info recorded in posts here will likely help others at some point. 

 

Regards, 

Michael 



#8 wdhensley

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Posted 17 March 2024 - 03:24 PM

Hi Michael,

 

First off ... thanks for your detailed reply.  I think I made an error in saying it was the DEC Motor ... it is really the RA motor.

 

Looking at the board, there are no signs of things being burnt ... not discoloration.  I posted some images of the board in the previous post.

 

In terms of taking measurements of the windings and shorts, I am not really certain how to do that.  I have put a meter across the red and black wires and checked for continuity and there is ... when I measure resistance, it is like 3.6 ohms.  When I check for shorts between either wire and the motor casing there doesn't appear to be a short

 

In the past, I have been able to take the cover off the of the gears and have been able to turn them with ease.  This time, I can't move them at all.  so that is why I took the RA motor completely out of the housing and tried to turn it ... it will not budge.  That is why I am suspect of the motor. 

 

To give you some history of the mount:

Purchased June 2017

Use - Prior to moving to Michigan, I lived in Arizona and would probably use it one or two evening a week.  In Michigan, I would say several times a month (weather isn't very good in Michigan for regular observing). 

OTA - Stellarvue SV-130 Triplet, Feathertouch focuser, SBIG STF-8300 camera Piggyback scope - Stellarvue 80mm imaging system with ASI2600MC camera

The system is reasonably balance if anything it might be a little tail heavy.  The tripod is on dolly wheels and the system out of the garage to my driveway for imaging so it is not permanent.

The system was connected to my computer using the skyX,  I had collected images of M42 earlier and change to Bodes galaxies.

 

The motors seemed to sound normal, didn't sound like there was any strain on them.

 

I really haven't had any other problems with the mount over the years ,,, the occasional runaway after finding home, GPS not getting a fix, but that is about it.

 

I was imaging Bodes Galaxies, when I decided to stop for the evening, problem occurred at the end of a session when I try to home the mount.  The DEC would home but not RA.  I brought the system back into the garage and tried to move RA ... it would not budge.

 

I would really like to get it working again.

 

Looking forward to reading other replies.

 

Regards,

Wayne


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#9 OzAndrewJ

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Posted 17 March 2024 - 04:44 PM

Gday Wayne

OK, that motor is definitely different and i have never heard anything about it.

The black box is the encoder, so open it up to have a look, esp if that is where the smell is.

It is on the unloaded end of the motor, but its bearing may have seized,

esp if you cant turn the shaft with the motor removed from the mount,

or maybe there are vents in the end so the smell just comes out there ???

The data i have for the encoder is it is an AVAGO  HEDS-5540 A02

but i dont have details on how easy it is to remove the cover.

 

As to the board, Michaels comment re double checking it is valid.

The normal mode of failure is the PCh mosfet dies ( big red arrow )

but it can also be a fault in the NCh mosfet or the transistor switches that drive them.

Soo have a really close look for burns or pimples

Andrew Johansen Melbourne Australia

 

MotorCard.jpg

 


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#10 wdhensley

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Posted 17 March 2024 - 06:29 PM

Hi Andrew,

 

Here is a closeup of the board ... it looks fine.

 

As for the motor, it is definitely seized up. 

 

I received a reply from Garry Ingle of MeadeMods.com and he indicates that " If you motor has ceased up than the motor control board has an issue. I do sell upgrade parts and motor encoder assembly‚Äôs.  Would be best to send in your mount for service and upgrades."  We talked on the phone about the service and I am going to send my mount to him to do all the repairs and upgrades for an LX-850.  Much much cheaper than replacing the mount that's for sure!  grin.gif

 

Thanks to the group for all the replies.  Will post updates when the mount is returned.

 

Regards,

Wayne

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#11 OzAndrewJ

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Posted 17 March 2024 - 06:58 PM

Gday Wayne

I dont know if Gary has worked on LX850s before, but they are very different to the LX200s

and their RA boards are not interchangeable without modification.

I see on your board the green jumper wires added to make the LX200 RA board

work with an LX850 RA wiring loom

Meade stuffed up the coding for the Home and PEC sensors,

and rather than fix the code they added jumper wires :-)

Also, as noted earlier, the motors and encoders are very different

and i have not heard of anyone working with them,

let alone having spares.

 

Edit.

As to the card being the problem, you can do a very quick test if you want.

Unplug the motor and set a multimeter in voltage mode onto the 2 pins on the board

Start the mount into the 444 test mode.

In this mode, nothing "automated" will start

Mode past the first test of sensors and LEDs

In the motor test, press the up/down keys and the DEC motor should move.

Now use the left/right keys

The multimeter should ramp up to +12V or -12V depending on key used.

If that happens, the board is probably working OK.

 

Andrew Johansen Melbourne Australia


Edited by OzAndrewJ, 17 March 2024 - 07:03 PM.


#12 wdhensley

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Posted 17 March 2024 - 07:22 PM

Thanks for the info Andrew,

 

I talked with Garry on the phone about the repairs.  He is a now a vendor for the motors (different numbers than that of Meade's motors).  The encoders are pare of the motors and he has them in inventory as well as the boards.  He has worked on LX-90s, LX-200s as well as LX-850s and a multitude of other systems.  I feel pretty good about my conversation with him and feel confident that he can repair it.

 

I appreciate the info on testing the board.  Either way I need to send it in for repairs.  If the board is bad, he can replace that as well.

 

Regards,

Wayne



#13 OzAndrewJ

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Posted 17 March 2024 - 07:34 PM

Gday Wayne

OK, sounds like he is up to speed on them.

Just wanted to be sure as i havent heard of anyone working with LX850s

as they are very different to the LX200s in subtle ways

 

Andrew Johansen Melbourne Australia



#14 MikeBY

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Posted 20 March 2024 - 01:33 AM

Hi Wayne,

Thanks for the background info and circumstances of the failure. Also for clarifying It's the RA motor

It's the first time I've heard of a failure like this going from working to completely locked up with no prior symptoms. 

Good to know Gary works on the 850s

I'll watch for your updates.

Michael 



#15 wdhensley

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Posted 29 March 2024 - 09:36 AM

Update on my LX-850 Mount.

 

The mount has been received by Meadmods and is currently on the bench.  The RA motor was probably burned up because of a shaft that got too hot and seized up.  The shaft has been polished and the gear installed.  You can now move the gears with one finger.  When the issue occurred, you couldn't move the gears by hand.  There is significant play in the mount ... this will be resolved with some updates and RA & DEC motor assembly adjustments. 

 

More to follow.

 

Wayne



#16 wdhensley

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Posted 03 April 2024 - 07:33 PM

Update on my LX-850.

 

I was just informed that my LX-850 is being shipped back tomorrow.  the bad RA motor has been replaced and works great!.  MeadeMods went through the mount completely, re-lubing, adjusting all clutches, backlash, and gear mesh and adjusted the homing sensors.  I also had him do his upgrades to the allen head locking bolts.  I now have rosette knobs, new RA locking bolts with handles, DEC & RA clutch knobs and much more.  I am very anxious to get it back and set up.  He stayed in touch with me almost daily giving me status updates and pictures.  I believe him to be a very reputable man and very knowledgeable about the LX-850 mount.  I understand he also works on LX-200a, LX-90 and I think some Celestron mounts.

 

Will let everyone know how it performs when I get it back and set up.

 

Wayne




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