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My Adventures in Fixing a Meade LXD75 Mount


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The Meade LXD75 (CG5 class) mount has been around a while and although there is a lot of information online about it. After some intense quality time with it I thought I might give some of my impressions.

Some background about me:

Having always been a space enthusiast, I did not get started using a telescope until 2002. I purchased a Meade ETX-125EC for the Mars opposition and though I had the basic EPs that came with the scope and really didn’t see much of anything with the skyglow from the light dome of NYC which is 40 miles away, that first glimpse at the Martian polar cap had me hooked. Since then I replaced the fork on the ETX with a Meade LXD75, then I sold the ETX and added a Hardin 10” dob, a William Optics SD66, and a stable of four 8” SCTs (one Meade, three Celestron) in various working condition. Originally I bought into the hype and was a Meade guy but I have since become wiser in my ways.

I have also been a member of the Rockland Astronomy Club since attending my first NEAF in 2004 (though I’m not currently a very active member.)

Some background about the mount:

I purchased the LXD75 mount used in June of 2006 and I'm not sure if the seller was the original owner so I'm not sure of its vintage. The mount did not come in its standard configuration as it had the WarpsDrive modification to the motor drives, three 10lbs weights (it normally comes with two) and the tripod that was included in the sale was from a Celestron CG-5GT with the 2" steel legs and the spreader/eyepiece tray. The mount also had an illuminated polar scope, which was obviously not standard as the black plastic cover for that end of the RA mount had a rough cutout made in it so that the illuminator could stay connected while covered.

Originally purchased to replace the broken fork mount on my Meade ETX-125, I have since upgraded to a Celestron C8 OTA and have a William Optics SD66 piggybacked for wide field or guiding. With the exception of a heavy vibration when making guide corrections in the east RA direction, I was operating the mount successfully until September this year when it began misbehaving by running backward from the direction I was trying to point it and then running at full speed regardless of the speed setting on the Autostar hand controller. I contacted Meade support to try to get a diagnosis but, having been unemployed since February, I did not have the funds to ship it to them for repair. Thus began my journey of disassembling and rebuilding it. I replaced the final screw the first week of December. Why did it take so long? When you only have a few minutes each day between looking for work and caring for three children under 5, you do things when you can.

Poor thought processes:

I started troubleshooting the mount by attempting to reset the hand controller to factory defaults which did absolutely nothing. Thinking that the hand controller had gone south, I purchased a used known-good controller to replace it hoping that that would solve the problem which it didn't. After trolling the internet for some possible solutions, the consensus of what I read indicated that the electronics on the main board that is housed in the RA drive probably burned out so I then continued on the spending spree to acquire a replacement RA drive. Before even attaching the new drive to the mount I tested it with the new hand controller. Much to my consternation, the same problem was there with the all new [to me] hardware. I then tried all of the combinations between the two RA drive assemblies and the new and old hand controllers and every time I received the same result. More reading online and some direct advice from very well respected members of the amateur astronomy community indicated that I should replace the encoders on the drives.

When all was said and done I realized that when the problems first started I had swapped out the power supply with another one that I had so I could use some dew strips that I had received in trade when I sold the ETX. Once I put the original power supply back the motors worked correctly.

Poor timing:

While I was waiting for the new RA drive to arrive I had noticed that the mount still had a fair amount of the green goo that Meade passes off for lubrication. Every forum I've read says that that goo should be cleaned off and the mount should be greased with a decent lubricant. Following the directions on Astronomyboy's website I began disassembling the mount and cleaning it up.

One of the major differences between the standard CG-5 mount and the Meade LXD75 is that the Meade design has the inclusion of ball bearings (four different ones, as it turns out) in both of the axis.

Rebuilding and discovery:

Without thinking about it I removed the ball bearings from the Dec housing, and in doing so severely damaged the large 6811Z bearing to the point where it had to be replaced. The soft metal shield that covers the ball bearings became bent into the path of the internal raceway for the steel balls. The smaller 6906Z bearing on the counterweight side of the Dec housing had some cosmetic damage but was still very smooth and functional. Note to all - do not attempt to remove a bearing using a screw driver and hammer. I ordered a replacement 6811Z bearing from VXB.com and cleaned the Dec components until the new bearing arrived.

Once I cleaned the dec elements up I was very surprised by the condition of the parts. With the exception of the bearings, ring gears, and worms, all of the metal parts are sand cast instead of machined. Cast parts are formed by pouring liquid metal into a form constructed of compressed sand or wax, rather than being machined from a solid billet of metal. I guess asking for machined metal in a class of mount this inexpensive is asking for a bit much, but the parts should at least be QA'ed once they cool. As you can see in Figures 1 and 2 there is a relatively large void in the axis itself which would not bother me so much if it weren't for the fact that the void is on a mating surface where it rubs against another surface. A void this big in this location should have sent the axis into the re-melt-and-use-again bin.

Figure 1 - Pits

Figure 2 – Missing Metal

All of the mating surfaces were very dark grey and some surfaces had some pretty large scratches in them. Following the instructions I sanded the bearing surfaces with some 240 grit sandpaper to get rid of the rough surfaces. The flash makes it difficult but you might be able to see the difference in Figure 3. When you use 240 grit to make something smooth, you know it was pretty rough to begin with. The poured metal is also very brittle as I later found out.

Figure 3 – Sanded surfaces

Both of the axes have clear plastic washers at various locations within the assembly. In cleaning the parts I could see some significant scarring on the washers, as if there were still some grit from the manufacturing process in the assembly. Some were so scarred they needed to be replaced. I also had inadvertently bent one of the washers while cleaning it, so in addition to ordering the new encoders from Deep Space Products, I also ordered their Teflon bearing replacement kit.

Even the ring gears were disappointing. I cleaned the inside of the teeth with a tooth brush as directed and the toothbrush left some fine striations on the aluminum gear. See Figure 4.

Figure 4 – Marks on the ring gear

When the new bearing came in, I began to reassemble the Dec axis, but again, while attempting to re-insert the new bearing without the proper tools, I damaged the new bearing. And the Dec housing. The pieces of the housing that broke off are hidden by the setting circles See Figure 6, but it is annoying nonetheless. Order up another 6811Z bearing.

Figure 5 – The dead bearings

Figure 6 – Damage to the Housing

To get the bearings back into the housing I built a press (Figure 7) out of 1/2" threaded rod and nuts purchased from one of the big hardware stores and some 3/4" thick hardwood floor s****s that I had lying around the house. I roughly cut the circles using my miter saw and used an orbital sander to get them to the proper diameter. Did I mention I don't have the proper tools? I used a socket wrench and crescent wrench to perform the compression and it worked pretty well except for when the pressing circle wasn't quite centered and proceeded to break apart as I put the large bearing back in. I wound up having to use the ring gear in place of the wood circle to press the bearing into place which I had wanted to avoid. I reassembled the parts and lubricated everything with some lithium grease I had lying around from another project.

Figure 7 – My press

I performed the same procedure on the RA assembly, but did not attempt to take large 6809Z and smaller 6807Z bearings out of the RA housing. Consider it lesson learned. I removed the old encoders and placed the new encoders onto the motors and proceeded to remount and adjust them so they operated smoothly.

Now that it's cleaned:

The motor housings need to be opened in order to make any adjustments with the motor, and this requires the removal of four Phillips-head screws. This is not a problem on the Dec motor, but on the RA motor two of the screws are hidden by the base of the mount itself with no access holes. You have to remove the entire RA motor assembly to be able to access the motor and worm which is a major pain. Two access holes would have been very welcome. I may add them in the future.

I attached the Dec motor housing back into place and adjusted the distance so that the belt was taught but not tight. Unfortunately, the connection point between the motor and its protective black housing is very thin plastic and in tightening the very small Allen screws the two (of the four) intact holes cracked, so now the plastic just kind of hangs there. I can live with that for now. The axis itself has some more friction than I would like, but it is light-years better than it was. The RA motor housing took a lot longer to get adjusted but is now very smooth.

A quick calibrate using the hand controller (and the right power supply) now has the mount working very well. I have yet to get it under the stars, but it feels ever so much better.

Disappointments:

Keeping in mind that the LXD75 is an entry-level mount, here are some of my qualms with the mount.

It's loud! My mount has the WarpsDrive conversion, which is reported to be quieter than the standard gearing from the factory, but even that is loud. I have the original gears, but no desire to put them back in for a comparison. Maybe the motors themselves are to blame, I don't know. At least I know that if any bears or skunks wander by I can scare them off by slewing to the other side of the sky.

As stated in the above the materials and build quality of the parts is pretty lacking. I know that with most things astronomy, you get what you pay for, but I would have hoped that a little more attention would have been given to making sure the contact points between elements were smooth and the lubricant used at the factory hadn't been something that came out of someone's nose. While there are plenty of aftermarket upgrades that can be done to the mount, we really shouldn't have to go through all of this trouble to make it work well. Some annoying design issues are also on my list including the inability to adjust the RA motor without having to disconnect the whole housing.

I know this is not really meant to be an astrophotography mount, but the lack of an ST-4 compatible guider connection is pretty glaring, especially considering that the competition has one. Instead of giving us an Aux port that no-one can seem to find a use for, replace it with a guider port.

Some built-in levels on the mount itself would be welcome as well. I detest having to take the whole thing apart to make sure the tripod is level and then re-assembling it. There are some aftermarket products out there with levels but it would be nice to have them right out of the box.

Things I like:

As far as computerized mounts go it's pretty inexpensive at under $600 new and it is pretty lightweight. I can lift the entire thing (tripod, mount, and attached OTAs) and haul it out the back door in one trip. Getting the rest of the setup out like EPs, computer, imagers, power, etc. is a whole other matter, but the mount is doable in one piece.

The menu driven Autostar handset is wonderful and it's nice to be able to add your own objects or elements. The only quibble with it is that computer memory these days is cheap, so there should be enough memory to hold all if not most of the major catalogs of objects that could possibly be seen with an under 30lbs. OTA that the mount is rated for.

The alignment routine is pretty simple and effective. On more than one occasion it has gotten me close enough that I had been able to keep clusters and planets in the center of the EP for over ten minutes unguided.

Conclusion:

It's a good entry level mount for visual work and its okay for astrophotography. The construction certainly has some issues as I mentioned. There are certainly better mounts, but this is near the top in its price class. The Celestron ASGT might be a little better choice for astrophotography, having a slightly higher capacity and an autoguider port, but the Meade LXD75 is certainly a viable option for a portable computer-driven mount.

Overall I spent just over $300 and over three months of my time fixing the $600 mount. It would have been less had I just sent it to Meade to begin with however, I have performed some upgrades and fixes that I probably would have had to do anyway.




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