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LX200 16" Specific Issues

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Subject: LX200 16"--Cannot Slew Using NESW on Handset and Drive Stops --part 1 of 2    Top

From: Martin Gaskell <> Date: Jan., 2000

Some months ago I asked the list if anyone else had run into the problem of the N-E-S-W buttons on the handset of an LX200 all failing to work and the drive tracking at twice sidereal rate.

Some people responded and basically said that the only solution was to return the unit to Meade and they would do something to the motherboard. I wanted to update the list on what happened with this problem. I will post several different e-mails with different subject headings to assist future searches.

After the usual difficulties in contacting Meade (which have been the subject of much complaining on this list), they eventually gave us an RGA ("returned goods authorization"), we shipped back the drive base, handset and dec. motor of our 16-inch LX200 and paid them in advance. A few weeks later everything was returned with no explanation of what had been done. At first everything worked, but on my second night of using the telescope the problem recurred. Since Meade had obviously not solved the problem (and in fact, as far as we could tell, had not changed anything on the telescope) we decided to try to find out ourselves what the problem was. In doing this we learned a number of things about LX200s which might be of interest to the list and which I will post separately. However, the answer to the problem of why the motherboard was failing turned out to be the ST-7 CCD autoguider. We are still working on this problem, and I'd be interested in knowing if anyone else has had this problem (no one mentioned the autoguider in earlier discussions of the problem). I'll discuss in my next e-mail how the autoguider is causing the LX200 to fail.


Subject: LX200 16" Cannot Slew Using NESW on Handset and Drive Stops --part 2 of 2   Top

From: Doc G, Date: Jan., 2000

When the LX200 runs at twice sidereal RA rate. it is because the West key or West command is being sent to the telescope. This command, when from an external guider, probably overrides any other keypad command. The problem should go away when the ST is not connected to the LX. If it does, then it is the ST which is sending the command. If not it's the LX that has a problem.

Note that the command is simply a shorting of one of the control lines to ground. Thus another problem might be a short in the cable or a defective connector on the LX or the ST. If you use a relay box of some sort, it might be a stuck relay.


Subject: LX200 16" Not Finding "Home" in Declination - Magnetic Sensor Alignment  Top

From: Martin Gaskell <>

(This is another brief note on an LX200 problem which might be of use to some users.)

After we re-installed the declination motor on our 16-inch LX200 we found that the telescope would fail to find home in declination. It is useful to know how the telescope finds home. The home position in declination (and I assume in RA too) is referenced to two magnetic sensors (Hall probes) and magnets. One of these is on the end of the worm gear. As soon as you turn the telescope on if you watch carefully you will see the worm turn slightly until it is aligned relative to the magnet. The other magnet is on the big gear and it gives the coarse position. When the telescope starts the "home find" it goes quickly 15 degrees in one direction and then comes back looking for the magnet. When it has found it overshoots and then comes back very slowly to center on it. If you have had to remove the declination motor (not something you should ordinarily do) and if you do not get the sensor which detects the magnet on the big gear in exactly the right place then it will not detect it and you will get a "home search failed" error message. The solution is to tinker with the positioning of the probe until the home search succeeds.


Subject: LX200 16" Power Flickering Off   Top

From: Martin Gaskell <>

(this is another in a series of short notes on problems we have had with out 16-inch LX200 and the solutions).

When we reinstalled the drive base after it had come back from Meade we found that it did not work. This proved simply to be because the ribbon cable connecting the front panel to the motherboard had come undone.

Later I also had the power flicker off erratically while testing the telescope at night. We traced this to shorting caused by the circuit board having come loose inside. The board is meant to be held down by some small plastic clips, but these had got broken in shipping. Putting in a new clip to stop the circuit board from touching the metal interior of the base solved the problem.


Subject: LX200 16" Declination Motion Binding  Top

From: Martin Gaskell <>

This is a short note on a minor problem with our 16-inch that might be of possible use to someone. When we got back our 16-inch LX200 drive base and declination motor back from Meade I found that the declination motion would bind at

some declinations. This was because the large declination gear is not perfectly round (or is slightly mis-centered). The problem is solved by loosening the worm gear a little. If it is too loose then there is an unacceptable amount of backlash. As far as I can now tell it works as well as when it was new (backlash in declination is about 6 seconds at fine guiding speed, more than ten times worse than my homemade telescope, but not problem).


Subject: Tips for Disassembling 16" Drive Base   Top

From: Assaf B <> Date: Jan 2002

Today I opened the drive base of our club's 16" LX200 for re-greasing. I left the fork base attached (didn't pry out the fork base from the bearings) but I do have a note or two, should it ever be needed for someone opening one of those scopes.

The most comfortable way to deal with the large piece is to put it on a few hard foam pieces with the "front" of the drive base facing you. Make sure the RA slow motion knob is free to rotate if you intend to clean (or rotate for any other reason) the RA gears.

a) In the 16" the printed boards (3 of them) are attached together to an aluminium plate which, in turn, is attached with 3 plastic clips to the bottom plate. After removing the 6 screws holding the bottom plate pull the remote end of the plate (the circular end) so that the lower end remains laying on the inner edge of the drive base.

b) You'll need to unplug :

  • the short ribbon cable (the larger ribbon connector goes between two of the boards and can be left in place).
  • two red connectors: one goes to the DEC socket in the front panel and the other to the RA drive.
  • two small (2 leads) red connectors which feeds the power to the motors: the one marked J3 goes to the RA drive and the J4 goes to the DEC drive (it joins the cable going to the DEC socket).

c) The motor can be powered directly with two or three 1.5v batteries in a comfortable rate to allow cleaning of the large gear, I didn't try higher voltage. The power should be fed to the black\white wires coming from the J3 connector, those wires goes directly to the motor.

d) When cleaning the gears be careful not to hit the right angle arm holding the magnetic sensor.

As in the other LX200 models, be sure to keep the sensors (two of them in each drive) clean from grease and be sure to mark a point on the RA wheel so that you can bring it back to the same spot.


Subject: 16" Drive Base Disassembly   Top

From: Assaf B <> Date: June 2002

I took apart the drive base of our club's 16" LX200 for cleaning and re-greasing. Here's a step-by-step list I wrote after the base was open and as I closed it back together. I hope I didn't forget any important detail. I hope this will be helpful for anyone who deals with those large scopes.

  1. Release the hex screw in the black cover plate covering the RA shaft and remove the cover plate, the retaining ring and the black ring underneath it (tip over the drive base and let it fall out).
  2. The most comfortable way to deal with the large piece is to put it on a few hard foam pieces with the "front" of the drive base facing you. Make sure the RA slow motion knob is free to rotate if you intend to clean (or rotate for any other reason) the RA gears.
  3. In the 16" the printed boards (3 of them) are attached together to an aluminum plate, which, in turn, is attached with 3 plastic clips to the bottom plate. After removing the 6 screws holding the bottom plate pull the remote end of the plate (the circular end) so that the lower end remains laying on the inner edge of the drive base.
  4. You'll need to unplug:
    -The short ribbon cable (the larger ribbon connector goes between two of the boards and can be left in place).
    -Two wide red connectors: one (J3) goes to the DEC socket in the front panel and the other (J2) to the RA drive.
    -Two small (2 leads) red connectors, which feed the power to the motors: the one marked J3 goes to the RA drive and the J4 goes to the DEC drive (it joins the cable going to the DEC socket). Use duct tape to secure the RA motor wires to the drive base body to protect them from damage in the following steps.
  5. Remove the spring from the worm assembly. Use a screw driver to push it out from between the two pieces of the worm assy'
  6. Use a sharp knife to mark the exact position of the worm assembly on the drive base housing. The unit I worked on had precise holes for the two screws holding it in place but if the holes are oval or larger (meant to allow fine tuning in the position of the worm with respect to the large RA gear) you should have marks so that youll know where excacly to put it back later.
  7. Take out the two hex screws holding the worm assembly to the drive base. Move the assembly so that it will clear the main gear. This is required for the gear to move out with the RA shaft. Secure the worm assembly to the drive base. You cant take it completely apart because of the 3 wires going to the main gear magnetic sensor. DO NOT touch the right-angled arm holding the sensor or it can be VERY difficult aligning it back to its position. Also be careful not to tear the delicate wires of the sensors. They are quite difficult (for me, at least...) to re-solder once broken.
  8. Connect the fork to the drive base using the supplied 4 bolts.
  9. Here I used pieces of wood to create wedges to support the fork from the sides (the lower sides of the arms, near the places where they are connected to the drive base). The height of the support wedges you use should hold the fork+drive base about 2 cm above the floor. Place pieces of foam underneath everything. The drive base will be released and fall about 0.5 cm (approx) once the shaft bearings are released.
  10. Open the black panel in the fork that hides the shaft (attached with 4 tiny hex screws).
  11. Tap the center of the shaft with a hammer. Place a piece of wood to prevent metal-to-metal hits that might damage the thread of the shaft.
  12. On some point the drive base will get loose and fall to the foam. On the unit I opened the upper bearing was released from both parts of the base and the lower bearing stayed attached to the lower section of the base (the static part).
  13. Disconnect the fork from the rotating section of the RA base.
  14. Take out the magnet threaded right next to the main gear. Its quite delicate and it is safer to put it aside until the re-assembly.
  15. The main RA gear can be left in its housing. If you dont take it out, however, it is a bit uncomfortable to open the 6 hex screws that are connecting the two assemblies: the one with the main RA gear and the other, with the RA setting circle and clutch.
  16. To get the setting circle out (and the slow motion tooth wheel and clutch) take out the 6 philips screws. Youll than be able to take out the large tooth wheel and underneath it youll find the clutch plate, held in place with two small hex screws.

The motor can be powered directly with 4 AA 1.5V batteries in a comfortable rate. After re-greasing its easy to connect the drive base to the fork, turn the whole thing up side down , connect the battery compartment leads to the motor leads and just leave the battery on the drive base so that the motor can do a few full rotations to each side to evenly spread the grease.

Re-assembly is a reversed procedure. It is comfortable, due to the size and weight of the parts, to connect the setting circle section (once re-assembled) to the fork (when its up side down) to ease the connection of the RA gear section (holding the setting circle itself in place). I also used the tipped over fork to connect the drive base housing onto the spinning assembly. I simply sled it over until the large bearing (that was in the bottom of the drive base) was fully seated onto the shaft. I then disconnected the drive base from the fork, tipped it over once again and inserted the upper bearing to its place with gentle tips of a wooden hammer handle. Make sure to tip all around the bearing to prevent it from getting stuck inside its housing. After the bearing is in return the black ring, the retaining ring and the black cap in place and youre all set.

One more tip: before setting up the scope again connect all the essential cords (power, DEC (from front panel to fork and from fork to DEC motor) and keypad to make sure it starts up OK. Its better to find any problem now before you lift this big and heavy scope and then find out it was for nothing.


Subject: 16" LX200 RA Drive Problem --part 1 of 4   Top

From: Paulo Cacella <> Date: May 2003

Jason, I have the same problem of RA drive errors, or something very similar, as I've seen in your images, but I'm sorry to say that I've not solved it yet.

I've tried everything you can imagine. Dismantled drives several times, tried every configuration imaginable. Today I am certain that it is related with gear/worm gear engaging. I do not know if a regrease can make things better or if you must make a tighter adjustment on axis but be aware. This is not a simple problem to solve. If someone had this experience before I would be very grateful with any tips.

  1. If like mine, this is NOT periodical error at all and CANNOT be overcome using PEC. In fact PEC makes things worse.
  2. Try to observe with oculars and see if it has a periodical behavior. Otherwise is better to change declination and verify if it has a sinusoidal pattern (as expected for PE ) or not.

If you solve this please make the solution available to the group.

-----Original Message-----
From: David Dixon: There is a DOS Qbasic executable that can read the LX200 16" PEC EEPROM into an file that can be manually modified and then the program can write the modified file back to the EEPROM. Not the simple process that PEC training is on the other models of LX200. Mr. Scott Roberts at Meade may be able to help those who need the program obtain a copy.


Subject: 16" LX200 RA Drive Problem --part 2

From: Sylvain Weiller <> Date: May 2003

Do you know about "astrosnap" software at:

Interesting functions are camera orientation, PEC measure, polar alignments. Use any webcam or video + frame grabber.


Subject: 16" LX200 RA Drive Problem --part 3

From: Gene Chimahusky <>

I took your supplied images and stacked them unregistered and also viewed them animated in IRIS.

If I got the math correct, using an ST-9 with 20u pixels at cass focus of a 16" f/10 the scale is 1arcsec/pixel. The images provided show what seem to be one cycle of the worm and the total excursion comes out at 10-11 arcsec.

Should better be expected? What is the worm period for the 16"? The image 9 is the far left of the excursion and image 13 is the final return with the intermediate ones tracking right then left.

No sign of dirt in the gears, at least the way it manifested itself on my smaller scope.


Subject: 16" LX200 RA Drive Problem --part 4 of 4

From: Doc G

>From many comments on this site over the years, you should be able to get
> about 5 arc seconds at best with excellent PEC training.

The period of the worm on the 16" is 4 minutes. That is because the 16" gear is 360 teeth instead of the 180 teeth on the smaller scopes.


Subject: Temperature Ratings of Components on Motherboard inside 16"    Top

From: Martin Gaskell <>

(this is another in a series of short notes on our experiences trouble shooting our 16-inch)

While trying to find out the cause of the misbehavior of our 16-inch, Bob Kelty, the head of our departmental electronics shop (and an EE Ph.D.) carried out extensive checks on the temperature sensitivity of components inside the base (Bob builds circuits meant to operate below the polar ice in the Arctic so he's very knowledgeable about the effects of extreme cold on circuits!).

Since our problem with the N-S-E-W buttons failing (see other posts to this list) first occurred on cold nights one of our first suspicions was that temperature was a problem (it can get well below 0 F (about -18 C) in Nebraska on clear winter nights). Temperature proved not to be the problem (Bob chilled almost every single chip with a circuit cooler spray), but people using LX200s in cold climates might like to know that on looking up the chips on the board Bob did notice that some were being operated well below their specified temperature ranges. This was not a problem for us, but it could be for someone.

By the way, the chip which is very HOT on the circuit board, is the voltage regulator chip (perhaps 40 C to 50 C on our board). This is normal and it has a heat sink. So long as it is putting out 18 volts, it's OK (ours was right on). On our board the voltage regulator chip is at the back left corner.


Subject: 16" Purchase Advise   Top

From: <>, Date: June, 1998

Hi Jerry, I would strongly advise getting a 16" LX200 OTA only, and a Paramount GT1100 mount to carry the tube. The 16" LX200 I had went back to Meade for a full refund after 8 months and three trips via truck freight, of Meade trying to get it to track with less than 20 arc seconds PE. It wouldn't point to better than 12 min. and the dec motor squealed like a pig when it got cold outside. I have some images that Scott Roberts made through this scope after they had reduced the PE from ~60 arc sec to 20 and can send you them via e-mail if you care to see how poor the mount really is.

The scope's tracking speed was not correct in quartz mode, but could be made to work in manual mode for short periods until the timing or the circuit became affected by the ambient temperature and drifted. This has been reported by others that bought this scope.

The optics on both OTAs that Meade put on the scope were awesome. I can attest to the fact that Meade's ability to make fantastic 16" SCT is beyond description and you really need to see through one of these scopes to appreciate what a 'good' large aperture, long focal length SCT can be capable of on a steady night. Truly impressive!! I could go on for a few hundred pages of raves about the optics. They absolutely got that nailed.

The mount and de-rotator is a miserable piece of work, and a real shame to put under such outstanding optics, but at ~$8k for the tube and < $10K for a Paramount you would truly have a "world class" instrument for under $20K. A bargain for sure. DO NOT buy the 16" LX200 unless the system can do as advertised and work out of the box as a unattended imaging machine and you have personally seen it (or anyone) do this.

If you try to do this with a stock 16" LX200 you will be very disappointed, it is not up to the task.......period! If Meade refines the LX200 portion of this scope it will be worth every penny, and then some. But for now the extra $3k is well spent on a Paramount and just the Meade 16" OTA.


Subject: 16" Mirror Removal    Top

From: Mogens Winthe

Doc G wrote :
>I simply must defer to someone who has actually taken the
>primary out of one of these and reassembled it successfully.

This is not an easy task. The primary settles on the focus tangential arm -- see:


On a 16 " this is merely locked by means of a tiny hex bolt - this primitive mounting method locks the focus arm - but demolishes the baffle tube thread.

In addition - the tangential arm seems mounted with locktite - anyone having experience in removing that focus tangential arm - contact me.

Unfortunately - in our case the primary mirror is loose. Tightening the focus tangent arm merely 5-10 degrees clockwise would be enough securing the mirror. However - this appears not to be possible - two persons could not move it even 1 degree.


Subject: Max load for a 16"   Top

From: Joe Hartley <> Date: Dec., 2000

Paulo de Almeida wrote:

> Can some one tell me what is the max load of a LX200 16"?
> I have a "Chinese" 150mm refractor OTA that I would like to
> pig-back on the LX200 16" will this cause any damage to the mechanics?

Properly balanced, the 16" will support up to about 45 pounds if I remember correctly. We were going to piggy-back a 7" Astro-Physics Starfire, and it would have handled that OK.


Subject: LX200 16" OTA Dimensions    Top

From: Remi Lacasse <>

The OTA diameter is 17.25". The total tube lenght is 30.75" with the pivot point of the DEC axis 12" from the back plate of the tube. The fork clearance from the DEC axix is 23".


Subject: 16" LX200 CCD Connector Pin Out    Top

From: Doug Carroll <> Date: Aug 2001

The instruction manual is almost correct except the pins are labeled correctly, but they are not in the correct order.

Looking at the CCD connector on your scope the Pin out is: 6 3 5 2 4 1

What Meade shows is the pin out in numerical order:

Pin 1 - Normally closed
Pin 2 - West
Pin 3 - North
Pin 4 - GROUND
Pin 5 - South
Pin 6 - East

So to correct this, here is the way it should look:

>Pin 1 - Normally closed
>Pin 4 - GROUND
>Pin 2 - West
>Pin 5 - South
>Pin 3 - North
>Pin 6 - East

On the 201XT Your looking at the Plug end so it is reversed. So they have this which matches the correct pinout but reversed and again named wrong:

Pin 1 - Right
Pin 2 - Up
Pin 3 - Down
Pin 4 - Left
Pin 5 - Grd
Pin 6 - +5V

So to correct this side, reverse the Pins and as in the Meade manual the pinout is wrong Bracketed () pins are the correct pin number:

*Pin 1(1) - +5V
*Pin 2(4) - Grd
*Pin 3(2) - Left (West)
*Pin 4(5) - Down (South)
*Pin 5(3) - Up (North)
*Pin 6(6) - Right (East)

I hope this all make sense The Pinout with the '>' in front is the correct pinout and numbering to connect it up correctly and comparing it and the one with the '*' in front you can see they are the same. So it's non-standard numbering going on as the problem.


Subject: 16" Classic--One or Two RS-232 Ports? --part 1 of 2  Top

From: Jim Duke <> Date: Nov 2003

-----Original Message-----
From: David Dixon <>
The LX200 classic: 7" thru 12" models have two RS-232 ports on the same RJ-11 connector, one is the PC serial port and the other a MISC serial port used for the derotator, or in my case dome control.
-----End of Original Message-----

The 16" LX200 "classic" according to the manual has the identical configuration and the same pin out. However I have been unable to communicate to the MISC serial port with the same cable that works with my 12" LX200, and the lack of the second port is a major problem for dome control. Can anyone verify that a second port does or doesn't exist and provide any assistance on using it if it does exist. Or how do others work around dome control with a single serial port?

The Technical Innovations Home Dome (DDW- Digital Dome Works) includes a Serial box which connects the LX200 Serial to both the DDW control box, and the PC. Also I think I've seen other posts talk a bout a way to split the port to two serial ports, but can't be sure.

For muliple serial ports on my laptop I use a USB to RS2s2 multiport hub, I've seen others using simple USB hubs and USB to serial adapters, but the RS232 hubs have additional buffering and stuff to help it be more reliable at high data speeds.


Subject: 16" Classic--One or Two RS-232 Ports? --part 2 of 2

From: Bob Denny <>

> Or how do others work around dome control with a single serial port?

This has been addressed by the ASCOM Initiative. There is a new Dome spec, a generic hub with built-in dome geometry and synch. Also, there is a version of DDWCP that ties into the ASCom Telescope interface and provides synch that way. Onlyone serial connnnection to the scope is required.

PS: <>
PPS: ACP1 pre-dates the relevant ASCOM standards and won't work with the above.


Subject: EZ Focus Kit for 16" LX200    Top

From: Pete Peterson <> Date: Aug 2001

We've had a number of 16" owners ask for an EZ Focus Kit, and they asked for a MAPUG notification if one became available. A special version of the EZ Focus Kit is now available for the 16" LX200. Price will be the same as the kits for the smaller scopes - $30

Our beta test site reported that the focusing action was much smoother and easier with the kit installed. Apparently there's no significant focuser backlash in the 16" because of the very heavy mirror cell spring preload, but this same heavy spring causes the focuser action to be stiff with the Meade standard setup. The EZ kit corrected that big time.


The EZ Focus Kit is a modification of Meade's focus mechanism. It does two things: it significantly reduces focuser backlash, and it provides a light precise feel to the focuser.

On the 12" and 16" scopes, there is a spring behind the mirror cell. This spring counterbalances the mirror weight so that there isn't a huge force on the focuser, and it also serves to reduce mirror flop. Mirror flop is associated with the fit of mirror/cell assembly onto the scope's baffle tube. There is a very special all temperature grease between these 2 parts, and if the grease is properly distributed it will reduce the effect of the gap between the 2 parts. It is this gap that causes mirror flop.

The EZ Focus Kit therefore, does not directly address mirror flop. But during the EZ installation procedure, since the scope is already partially apart, we do provide instructions for redistributing the grease between the baffle tube and the mirror/cell assembly. And redistributing the grease has been known to reduce mirror flop.

The comments of our 16" beta tester were mostly about a very significant improvement in the focusing action brought about by substitution of the thrust bearings for the greased nylon washers that come with the focuser. Apparently that mirror spring is a really big one in the 16", and it generates a lot of friction, making the focuser action stiff.


Subject: 16" LX200 Focuser Fix   Top

From: Bob Parry <> Date: Sept 2001

First, we removed the corrector (carefully} and after releasing the focusing rod, we removed the mirror by lifting the mirror out. There is a fairly healthy spring behind the mirror, but as I was lifting the mirror straight up it did not present any difficulties other than you must be strong enough to lift it.

Jack suggested that we install 6 spring detent set screws 3 in each end of the mirror support tube. These are threaded set screws with a spring loaded ball on the end. I drilled and tapped the six hole #10x24 making certain that the mirror was protected.

The fix is fairly simple once you have the mirror out of the tube. It involves drilling and tapping three equally spaced holes about 3/4" (20mm) from the top and bottom of the tube that the mirror slides along. Insert into these holes set screws with a spring loaded ball at the end. These are not that difficult to find, Industrial Fastener Suppliers should have them. Home-Depot?? maybe. This is obvious but having had projects built over the phone in the past I try and reduce errors at the beginning. Buy the set screws BEFORE you tap the holes! and match the hole thread to the set screw.

Reinstalling the mirror was a little tricky with the detents making the fit very tight, but rotating the mirror assembly as I pushed down gently did the trick. The mirror now no longer shifts and focus remains true across the entire sky.

I have made a quick drawing of this procedure if you want it send me a note at <> and in what form you can read. The original is in AutoCad R14, but it can be saved in some others.


Subject: 16" Focus Mods   Top

From: Bob Parry <> Date: June 2002

I have a drawing detailing my modifications to the focus mechanics for the 16":

Focus Mods Diagram

Here's a download of an engineering drawing.


Subject: 16" Motion Limiting System   Top

From: Assaf Berwald <> Date: Nov 2001

The motion limiting switch is attached to a piece of wood that is glued to the fork arm.

The two limiting pieces are glued to the Dec circle and each of them is long enough so that even as the scope keeps slewing after the power is cut off due to its momentum, still there's no chance that the limiter will pass the motion limiting switch. This is to prevent a momentary shut-down of the scope (The idea is to keep the scope turned off until the user switches the bypass switch to return the scope to its safe working area).

Motion Limit Switchj

Photo-Control Box--
The switch and warning light are clearly visible, along with the wiring at the bottom of the box, going to the scope, microswitch and power supply.

Motion Control Box

Photo-Control Box Sketch--
In the photo of the control box you can see 5 wires going out of the box instead of two or so just because I did some messy job installing the box.

Motion Control Sketch


Subject: PEC Retraining on LX200 16"  Top

From: Arto Oksanen <> Date: Nov 2001
                            or <>

There is a QBASIC program to do the trick. It is by no way an automatic procedure as with the smaller LX200s with a keypad, but the software allows to download the PEC table from the telescope to the computer as a file and then you can manually modify the values before sending it back to the telescope.

I have a copy of this software, so if anyone needs it just drop an email. You'll need an old WIN3.1 to run QBASIC.


Subject:16' LX200 Classic PEC Problem --part 1 of 3  Top

From: Mike Gerszewski <> date: July 2004

James Marsden wrote:
Mike, you need to determine the source of the PEC problem before trying to correct it. To do this, you need to accurately record the PEC error over a couple of worm cycles, which would mean for at least eight to ten minutes.

If you have a camera that can guide and also allows you to record the guide errors or corrections to a file, then you can use this procedure to analyze your PEC.

1. Disable PEC

2. If possible, use a h-alpha filter on your camera. if you do not have h-alpha, then use a red filter. This will reduce seeing effects on guiding.

3. Use a star near the intersection of the celestial equator or near the meridian, preferably an hour left or right so that the meridian is not crossed during recording which can a 'jump' as the weight shifts. Use a guide star that is bright but does not saturate the detector.

4. Enable guiding but set the gain, to zero or as low as possible so that the camera does not actually cause the scope to be guided. You only want to measures and record the guiding error, not correct for it.

5. Guide at 0.5 sec or 1.0 sec depending on the guide star brightness.

6. Record guide errors for at least two worm cycles - long enough to get 512 samples at 1.0 second guiding or 1024 samples at 0.5 second guiding.

7. Do a fourier transform on the data. determine at what frequency the guiding error is occurring. It may not be at the worm rotation frequency but at the frequency of one of the reduction gears in the motor gear reducer. If it is, the you need to clean the gear train or replace it.

8. If you have recently added something to the scope or rebalanced it, you may also have changed the loading on the gear train which could change your PEC.

------end of quote-----------

Response: great advice. This is somewhat like what I was planning on doing, but you have described it very well.
A couple of points:

>1. Disable PEC

This is what i need the software for. the 16-inch's PEC is factory set and always on, and there is no way to turn it off without completely deleting the settings. Meade released the API for it, and I know of at least one person who has written software to read and write the PEC corrections, but can't find the software anywhere (might just have to write my own...). I have heard that it can be deleted through the hidden menu, but I want a copy of the settings to look at before I delete the settings...

> 7. Do a fourier transform on the data. determine at what frequency the
> guiding error is occurring. it may not be at the worm rotation frequency but
> at the frequency of one of the reduction gears in the motor gear reducer. if
> it is, the you need to clean the gear train or replace it.

Just so everyone's on the same page here, the 16" doesn't have a gear train like the smaller scopes. It has a motor direct driving a belt which drives the worm. So the only sources of PEC issues are the worm and main axis gear, assuming the motor and belt are working properly. But i will remember your advice for our smaller scopes if a similar problem occurs.


I now have some hard data. here are the links to the graphs:

There are some noisy points where MaximDL thought it had the star in the field, but it really wasn't. Y values on both graphs are change from the avg pixel location in that axis. The CCD is oriented almost orthogonal to the telescope's ra/dec axes. x is ra, y is dec.

A bit of analysis:
First off, there is a definite sinusoidal pattern in ra (x), that drifts somewhat. I don't see anything that would have caused the barbell-look in the image, except that the top of one of the curves looks flat. The period is approximately 4 minutes, but if I get more data over a longer period, I may be able to tell if it is maybe a flat/peaked oscillation.

Is it possible that PEC miscorrections are causing this?

Are the PEC settings for the 100-second flat interval fine, as it stays approximately 1 pixel away from avg throughout almost the entire interval, and within about .5 pixel of each other throughout that interval?

Since it is repeatable, would guiding reduce this issue?

Both graphs show that our polar alignment is slightly off the delta y graph has a calculated drift of 0.03 arcseconds/second. The delta x graph also shows a definite drift, but less pronounced at about 0.007 arcseconds/second.

What do you think, are the PEC corrections in RA just somehow way off? Could the PEC corrections in RA be compounding any polar misalignment if they collectively add up to a drift?

I really need that software to read off the PEC settings so i can see if it corresponds to the changes seen in the graph.


Subject:16' LX200 Classic PEC Problem --part 2 of 3

Jim Burrows wrote:
> this says, I guess, if you were to do a perfect PEC with the worm
> contacting the worm wheel at one position, the runout would make it look
> bad at another contact position (PEC would cure scale factor error).

We certainly don't expect perfect PEC, but right now, it is virtually unusable. Some of the 60-second images are sometimes shaken by PEC miscorrections (two mostly circular endpoints connected by a thinner line).

> maybe Meade uses better gears for the 16". Just for curiosity, it might
> be interesting to run TPoint to see what it says about these gear errors.

The axis gears in the 16" are 11" in diameter, and the worms are pretty large too. Also I believe they have a 4-minute worm, as opposed to the 8-minute worm used on the smaller scopes. Actually, we didn't have a problem until recently. A couple of years ago after a good polar alignment we were able to take 5-minute CCD images at .46 arcseconds/pix without trailing. Something happened recently to throw the PEC off.

We don't have TPoint, unfortunately. I could probably track it with the guider to see how much a star moves during the 4-minute period. In fact, that was the method I was thinking of using to re-program it. read the current values, save them to a file, clear the PEC, and then use the CCD guider to see what kind of corrections are needed.


Subject:16' LX200 Classic PEC Problem --part 3 of 3   Top

From: Doc G

I have adjusted the belt on one of the drives. You need to be sure the belt is very tight; especially if the scope is old. these belts stretch with age and use. I had to make a significant adjustment of the motor to get the belt tight enough. They are a standard belts; so you should have no trouble getting new ones from a gear house. One of our belts actually jumped a cog from time to time. That is very much too loose.

The motor actually has gears. If you scope is like ours, it has a Pittman gear head motor. The gears are there but are inside the gear reduction head. You can tell if it is the gear head or the worm by looking at the shape of the errors you are getting. If it is a gear, it will repeat at 4 minutes and be rather sinusoidal looking. If it is the worm it is likely to have some good spots and some large and sudden jumps. yYour description of two star images connected by a line suggest a bad worm to me. Also you need to note that the wiggles over a single turn of the worm, four minutes for the 16" scope, are entirely due to defects in the worm. The worm pushes on only one tooth of the main gear because it is a spur gear and not a true worm wheel. A true worm wheel has a surface of contact with the worm since it is a throated gear. I have not worked on the mechanics of the 16" yet; but will be doing so soon.

The worm can be severely damaged if you allow the worm to disengage from the large spur gear. The jumping of the gear will pond flat spots on the very edges of the worm that are doing the guiding. The smoothness of the worm has to be in the sub-micron range to get arc-second tracking. The best I have ever seen in an LX200 is 3 to 5 arc seconds after a very good PEC training. I have polished both worms and spur gears in several LX200 scopes. These can be improved significantly. In the honing/polishing procedure, the worm and the gear are both ground together to make a pair. This is a major task which only experienced instrument makers should attempt. It can be done.

Iam sorry to report this; but, I think your tracking goal is highly optimistic and you will find it almost impossible to get this sort of tracking with the LX200 mount. That is even with excellent PEC training. We are putting our 16" optical tube on a Paramount for that reason.

Additionally, the fork is too subject to vibrations and oscillations for consistent imaging. I strongly suggest you get an SBIG camera with an AO unit to do precision imaging with this mount.


Subject: 16" LX200GPS & ST-9 with Derotator?   Top

From: Mark de Regt <> Date: Jan 2003

Andreas Philipp asked:
> I want to build up an observatory of digital imaging by using a 16" LX200
> with field derotator, f/6.3 reducer and ST-9. Does this combination work
> without problems, especially the autoguiding with the ST-9 and the field derotation?

Andreas-- I image with a 10" LX200 at f/12, using an ST-8E camera, guiding through the AO-7. I have never used a field derotator, but I consistently hear that, at best, a field derotator complicates things considerably, and at worst, simply do not work well. If you are going to get a scope as large as a 16" LX200, you will not be moving it a whole lot; I would guess that you will mount it on a pier and leave it there. I would strongly recommend permanently mounting it on a polar mount.

I think that a reducer is fine as part of your arsenal, but I would also highly recommend getting an AO-7, and imaging at f/10 whenever conditions permit. The AO-7 is a miracle worker with the LX200 mount. I think that you will be disappointed in time by the low resolution you will get with the large pixels on the ST-9E.

You might also consider some smaller OTAs, like the Meade 12" or 14", or the Celestron 14", and mounting it on a good mount (like the AP1200GTO or the Bisque Millennium). The combination would not cost much more than a 16" LX200, and you might like the added flexibility.


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