RA Drive Concerns --Page 1

       

Subject: RA Drive Problem Experience  

From: Kevin Dougherty PLEIADE0aol.com

It turns out that the noise and vibration I experienced were not related to a worm/screw drive grease deficiency -- the noise was clearly coming from either the RA motor or gear box. I removed the motor assembly and in the process managed to loosen the mask in front of the diodes (it actually looks like a small broken piece of black sheet metal) - and as Doc G explains in the archives, it is VERY difficult to reposition properly. It probably wouldn't have mattered anyway since I think I had a problem with the motor or gear assembly - so I've just sent my electronics back to Meade for the $200 replacement package.

A couple of things I learned:

1. I did reassemble the mask pretty closely to factory - as evidenced by marks on the housing. However, close is not close enough - the drive acted erratically when reassembled and pointing accuracy was terrible (well outside of 20 MM Super wide field of view). Also the scope would jump in RA every few seconds. This leads me to suspect that the tolerance of accurate placement of that simple little mask can have a significant influence on pointing accuracy.
2. If you have a really really good reason to open up the scope and work on the drive motors, DO NOT LOOSEN THE 4 ALLEN SCREWS HOLDING THE COVER OF THE GEAR BOX - it is only their tension that holds this mask in place - once it moves, my bet is that you are probably in for the $200 repair special and loss of scope function for 2-3 weeks. There is a flexible cover on one side you can peel back to look at the gears instead, although this approach doesn't give you full access to the assembly.
3. In speaking with Ozzie at Meade over all of this and discussing the original problem he mentioned that in addition to the grease fix, tension is also controlled by a straight blade screw in the end of the screw drive. Another item to keep in mind if you experience problems with the drives.

Subject: RA Drive Noise Fix   

From: Rob Roy <rroyexeculink.com>

I recently posted that my RA drive was making a new noise. It was cured by regreasing the gear. The drive doesn't need to be taken apart to regrease the gear.

To get at it, lay your scope on its side on a workbench with the base's control panel facing up. Remove the four Philips screws and the two tiny hex-head screws which hold the base plate. Take off the base plate and carefully disconnect the large ribbon cable. You can now get at the main RA gear quite easily.

Disconnect the RA lock, plug in your scope and start it up (Dec cable not necessary.) You can now apply grease in short sections and move the gear around with your keypad E/W buttons (scope itself will not move with RA lock unlocked.) I put a small red dot on the gear so I would know when that spot came around again.

Subject: RA Drive Noise Caused by Metal Chips  

From: Doc G, Date: Apr 2001

Once you take the electronics out, the rest is easy. You have a few very robust mechanical parts. Just take it apart, and remove the grease on the gear with some solvent. Mineral spirits is fine or use carbo chlor. These are available at any hardware store. I use a tooth brush to scrub the parts clean.

Do the operation on a nice bath towel (an old one) and do not drop the gear on a concrete floor and you will be fine. The easiest way to get it apart is to tip the base on its side on a towel so it does not slide around easily. Then take a short piece of 3/4 inch wooden dowel and a hammer and tap the worm wheel from the bottom. If you tap it firmly and turn the FMS with respect to the base, you can little by little force the two parts apart. Be sure to tap it firmly an all around the edge so it does not jam crooked. Suddenly, the two pieces will fall apart as the bearings release the

When the parts are clean, regrease the gear and reassemble. See pictures on my website under the LX200 Information /
  LX200 Mechanical Analysis section

It is really easy and should only take an hour to get a nice clean smooth RA axis drive. In fact, it is really a lot of fun to take these things apart. You will understand your telescope mechanics much better afterward. And, most important you will have a clean and smooth RA drive. Not to worry, this is not like taking apart a watch.

> How does one adjust the worm when reinstalling?

A good start is to center the worm against the big gear and snug it up against the gear. Then tighten the two holding bolts. The platform should have a tiny amount of play. I would say 1 mm at most. The RA gear is generally very nicely round and cannot wobble from side to side like the Dec gear.

While you have the drive out, check for any looseness in the worm and platform bearings. If has slop, just tighten the end screws a tiny bit. Do not tighten them enough to make them bind. When done everything should be smoothly moving but with no end play.

Meade does use Loktite in certain critical spots. If you have a problem loosening a bolt or screw, you need to do two things. Use a very well fitting screwdriver, new Allen wrench or whatever tool is appropriate. And, apply heat as necessary to soften the Loktite. A small torch, a large soldering iron or a large gun type soldering iron will usually work well. Do not be afraid to heat the part holding the screw thoroughly. A real disaster is ending up with a stripped Allen head screw. Use an Allen wrench with a T handle and push it into the offending screw very hard.

Subject: RA Drive (classic) Repair, How It Works   

From: Bill Miller

Being an engineer, I enjoy understanding the vehicle (LX200) as much as I do understanding the journey (through our universe). So let me know if this technical detail is of interest. It's a lot of work to improve or fix equipment, easy to damage something, and getting parts is real difficult. Reverse engineering from ground zero takes a lot of time. It's time I share my experience with MAPUG.

My rev 4.3 LX200 12 inch which is pier mounted was working just fine until the evening I inadvertently turned on it's power from inside the house and it spent the night outside wrapping itself in its cords and cover until the RA drive motor stalled. I'm glad the cords were anchored securely so the ST-7 CCD camera and NGF-S motorized focuser did not get ripped off.

Upon discovery and fearing the consequences of my negligence, I said to myself, it's a good thing the fuse in the LX200 power panel is there. To no avail the 2 amp fuse did not blow. So I've replaced it with a 1 amp fuse in hopes to prevent any future catastrophe.

Damage was as follows:

The 1 watt resistor to the RA motor was really cooked, PC board darkened under it. It measured 0.8 ohm. I took it off and installed a 2 ohm 3 watt resistor since 2 ohms is on the Dec motor's circuit.

RA motor windings of the rotor were burned out, open circuit. I opened up the gear box. Pulling off the gear/strobe disk from motor shaft was done by using a 14 gauge bicycle spoke's threaded end to drive down into the 0.079 inch hole in the top of the strobe disk/gear assembly (while holding the motor shaft) and it pushing the motor shaft out. I ordered some Mabuchi motors from Edmund Scientific, but the 18v motor had 59ohms resistance and the 6v motor had 0.5ohms. What I needed was 5ohms (probably 12v).

I put it all back together and powered it up. The system initializes now, but the L2724 chip must have an internal problem since its input is OK and it's output is intermittent. Getting that part is impossible. I found 3 major distributors. Orders are backlogged and there is a 99 week lead time! John did say Meade is in the business of selling scopes instead of parts. Any suggestions?

--------------------------------------------------------------------------------

This is the main board components (classic) that power the DC, barium ferrite magnet, Mabuchi motors:
   (Note: schematics are available at: <http://www.ccdguy.com/lx200/lx200.htm>

SGS-Thomson Microelectronics, L2724, 9 pin single inline package. Low drop dual power operational amplifier, pin2=18v, pin5=GND. The op amps drive the motor in push-pull fashion. Pins 8 & 7 are VCC/2 reference voltage inputs. The signal enters negative inputs 9 & 6 to form inverting amplifiers with gains of -2.7 and -1.0 respectively (-27K/10k and -10K/10K) with output 1 driving input 6, so the overall gain = 5.4. The 1ohm .22uf Boucherot cell and the 2ohm are for stability. There is one L2724 U18 for declination drive and one L2724 U17 for right ascension drive. The L2724 shuts down if it's temperature rises above 145 degC. With a continuous output current rating of 1amp it's capable of burning out the 2ohm resistor and the motor.

|--one L2724 from here-> |--one L2724 from here->The bottom cover plate of the LX200 is bolted to the L2724 heat sink to help keep these devices cool.VCC/2=ref>----------o------------------------------------------------------| | . . | | Op Amp >--o--2ohm--o----Motor----o--< Op Amp | |---| - . | | . - |---| VCC/2=ref>----------o------------------------------------------------------| | 8 | . |-1ohm--.22uf-| . | 7 | |---| + . 1 | | 3 . + |---| . 1 (RA) | 9 | . | | . | 6 | -| + . | | | | | Op Amp >--10Kohm--o----27Kohm-----o-------10Kohm---------o---------------| -| - . | . <------| . LM324N

• SGS-Thomson Microelectornics LM324N preamplifier U16 drives both L2724.
• Low power quad operational amplifier, 14 pin dual inline package,
• pin 4 =VCC=18v, pin 11 =GND. It's 4 op amps provide the following:
• pin 14 - VCC/2 reference voltage for both L2724, as illustrated above.
• pin 8 - Bias voltage 2.5v for AC coupled inputs of op amps on pins 1 & 7.
• pin 1 - Inverting Preamp for RA, gain = -27K/4.7K = -5.7
• pin 7 - Inverting Preamp for Dec, gain = -27K/4.7K = -5.7

--------------------------------------------------------------------------------

This is the drive unit board which detects flashes from the IR Light EmittingDiode shining through 90 slot rotating strobe disk mounted on motor shaft:

• New Japan Radio Co, 2901N, 14 pin dual inline package
• Quad single supply comparator (2 comparators are used) pin3=18v, pin12=GND.
• The circuit function is two inverting comparators with hysteresis.
• When input pins 4 or 6 go >2.84v, output pins 2 or 1 respectively go to 0v.
• When input pins 4 or 6 go <2.11v, output pins 2 or 1 respectively go to 5.0v.
• The 2901N comparator outputs are NPN pulldowns with the pullup provided by RN3
• 4.7Kohm resistors to 5.0v on the main board. When bench testing the drive
• without connection to the main board then only it's 27Kohm resistors pullup
• the comparator outputs and their Vtrip high and Vout high change as follows:
• When input pins 4 or 6 go >2.50v, output pins 2 or 1 respectively go to 0v.
• When input pins 4 or 6 go <2.11v, output pins 2 or 1 respectively go to 2.5v.
• IR detector bias current is adjusted by turning the 20Kohm potentiometers.

I found the pots set as follows: old RA unit 710ohm and 865ohm, replacement RA unit unit 323ohm and 274ohm, Dec drive unit 780ohm and 832ohm. Measure resistance with the power off. Turn the power on and with the motor running at moderate speed set the pots to get 2.1vDC 1.0vAC on CompIn4 and CompIn6. Then with the connector to the main board plugged in (or with 4.7Kohm pullupsadded) fine tune the pots to get 3.1vDC 2.3vAC on CompOut2 and CompOut1. What are the optimum voltages? I don't know. This is what got me up and running again. This adjustment changed the pots on my replacement RA driveunit from factory settings above to 331ohm and 318ohm respectively.

Access to the probe points to measure voltages is convenient. The 3 gold pin set on the corner of each drive's small printed circuit board (starting from the board corner) is CompIn6, CompIn4, and GND. The comparator outputs are the 27Kohm resistor leads sticking up (again from the corner) CompOut1 and CompOut2. The 5v supply is the 56ohm resistor lead sticking up.

The RA unit 2901N output pins 1 & 2 go to input pins 5 & 9 respectively of U13 a SGS-Thomson T74LS14B1 hex Schmitt trigger (hysterisis trips at 0.8v & 1.6v) located on the main board, then out of U13 pins 6 & 8, over to U12 pins 6 & 7 a XYLINX XC3030-70PC68C field programmable gate array.

The RA and Dec boards have identical circuitry, except the RA also contains a sensor located on the worm that sends 18v/GND signal to pin 9 of U11 another T74LS14B1 located on the main board. It's primary purpose is to let the periodic error correction know the position of the RA worm, and it may also be used in the power up self test. The worm shaft has a 1/8 inch hole drilled in it and a magnet inserted. Each time this magnet passes the Hall effect IC mounted next to the worm shaft a signal is sent out the white wire to the main board of the LX200. Since the switch is magnetic and not mechanical or optical any grease should not affect its operation.

5v >--------o-------------------o-----o-----| |<--- 2901N ---->|
regulator | | | |
78L05 | | | 10Kohm
56ohm 20Kpot<--| | |-------o-----27Kohm-----|
| | | | 10Kohm | 5 |
| Strobe Disk | | | | |----| + 2 | Black
| | | | | GND | Comp >----o----- LED ~~ DET | | 4 | |--GND | 10Kohm LED ~~ DET | |-------------o----27Kohm------| | | 20Kpot<--| 10Kohm | 7 | GND |-------o-----------------------------| - 6
| V |-------o-----------------------------| - | | | | |----| + 1 | Blue
| | | GND | Comp >----o-----

I have not yet determined the purpose of the duality of this control circuit. The 2 groups of slots in the detectors' mask do line up together with the slots in the strobe disk. Perhaps it is for redundancy and reliability. --------------------------------------------------------------------------------

When tracking, what speed are all the mechanical parts running?

1 rev / sidereal day on the RA axis. 365.24 sidereal days = 366.24 solar days.

1 rev / 8 min on the worm driving 180 teeth (180x).

1 rev / 2 min on the 11 tooth gear driving 44 teeth (4x).

2 rev / min on the 9 tooth gear driving 36 teeth (4x).

1 rev / 8 sec on the 8 tooth gear driving 30 teeth (3.75x), motor rpm.

11.25 slots / sec on the 90 slot strobe wheel (90x).

One revolution of scope axis = 972000 slots passing by on strobe wheel.

The above uses sidereal minutes and seconds = 1.0027 solar min and sec.

How many strobe wheel slots correspond to one angular arc second?

360 x 60 x 60 arc sec = 972000 slots = 1 revolution of scope

For DEC 1 arc sec = 0.75 slots 1 slot = 1.3333 arc sec.

For RA 1 arc sec = 0.75/cos(DEC) slots 1 slot = 1.3333 cos(DEC) arc sec.

How many strobe wheel slots correspond to one right ascension sidereal second?

24 x 60 x 60 RA sec = 972000 slots = 1 revolution of scope.

1 RA sec = 11.25 slots or 88.88 RA msec = 1 slot.

For the PEC's 8 min/200 = 2.4 second period = 27 slots.

What's the speed of the motor when slewing?

2 deg/sec slew rate = 1 rev/3 min on scope axis, 3600 rpm on motor.

8 deg/sec slew rate = 14400 rpm on motor, 21600 slots/sec on strobe.

No wonder it makes that notorious noise when slewing.

--------------------------------------------------------------------------------

Hope you enjoyed this. If anyone spots an error, please let me know. Again, I recommend you don't open up your scope unless you are willing to deal with all the consequences. Knowing how it works is satisfying enough.

Subject: LX200 Classic Runaway Condition -- Part 1 of 2  

From: Doc G, Date: April, 1999

Chris Vedeler wrote:
>Today I disassembled the RA drive again, only to find a small metal mask
>with two groups of three holes had fallen off. It was obvious where it
>came from as there was a clean spot on the metal right over the encoder
>diodes. I epoxied the mask back in place and then reassembled the RA
>drive. Confident that I had fixed the problem, I powered on the scope
>to make sure the motors acted normal before I put the bottom plate back
>on the LX200 and return it to it's happy home in my observatory.
>
>To my horror, the RA motor ran at full blast to the West. Nothing I
>could do to the control pad would stop it. If I pushed the E key with
>the scope set to slew, it would slow down from it's run away 8 degrees
>per second, but that was it. I have checked and rechecked the encoder
>and can't find anything obviously wrong with it.

Unfortunately the positioning of the encoder mask is not simple. It probably has to be placed within 0.01 mm of the correct position and at exactly the correct angle as well. I believe this is done in tuning up the original drive by having a mask with a long tab on it and placing the drive in a jig. The mask is then moved until the bi-phase signals are correct, as observed on an oscilloscope, the side plate is tightened and the long tab cut off. (you need a two channel oscilloscope to do this)
It is almost impossible to do this without a new encoder mask that has the tab. It can be done by trial an error, but it is difficult. You need to extend the tab with a tiny piece of sticky tape and then manipulate the encoder into place with the motor running. This can be done to the motor assembly on the bench. (not in the scope but powered) But proper equipment including an oscilloscope and suitable power supply are required. Meade has made it almost impossible for the normal user to repair the drives because of their basic design.
I wish I could give you better news. But home repair is exceedingly difficult except unless you are a near expert in electronics and encoders and have the proper equipment. Some of the problems are of course explained on my website.
------------------------------------------------------------------------------

Subject: LX200 Classic Runaway Condition -- Part 2 of 2  

From: B. S. Jones

I've had my LX200 now for about a year and for the most part it has work really well. About ten days ago I was using my system and the system would either continuously keep running in the east direction or it would not run in the east direction at all. I had my laptop hooked up to it and I was able to properly control the RA movement through the laptop and LX RS232 port. I called Meade and the technician and I agreed that this sounded like a bad keypad. So even though I was slightly out of the warranty period they shipped me a new key. The new keypad arrives and seems to work fine in land mode (couldn't wait to test at night). Well, I went out last night and everything seemed to work fine until I linked the laptop up to the LX and established the link. From that point on the LX demonstrated the same kind of behavior, either no response from the E key or would just flat keep running. All other keypad functions seemed to work OK and the laptop could easily still control the LX. On one of the restarts of the system as soon as the system went though its initialization it started slewing E and had to be turned off. I went through the MAPUG Topical Archives and was unable to find anything like this. I apologize in advance if this has already been covered on the list. Has anyone out there encountered this before?
If you look at LXcircuits there is a set of electronic circuits that cover most of the LX200, i.e., the external boards and the main computer board but not the power input header or the keypad at present. If you go to the LX200 part of my web page there are a set of circuits listed 1 to 9 get the image of circuit 9 and print it or look at it in a program such as Paint shop pro or some equivalent. If you look at the output pin of the device called MAGPIC in the circuit with a voltmeter as the worm wheel rotates this will go between +5 volts DC and zero volts DC for a short period in the rotation of the worm. This is a magnetic hall effect device that checks the position of the worm. If you also look with an oscilloscope at the pin 1 U2A and Pin 2 U2B there should be a set of square wave pulses on these outputs again at five volt levels. If all these signals are there then it is most likely a main board fault not on the motor header. It is possible for any one with basic tech experience to service this part of the circuit, not the same for the main board though...
Sorry about the hi tech answer but I do not know any other way.

Subject: New LX200 Classic RA Drive "Runaway" Cause  

From: Harry Gilday Date: March 2001

>Well I just unpacked and setup the new 12" for the first time. Turned it on
>and the RA drive continuously goes at a fast (slew?) pace. I turn it off,
>and wait a reasonable time, then on, and the same happens.
>
>I've found this site which seems to indicate this is "RA Drive Runaway".

I know exactly how you feel. When I got my LX200 12" that is exactly what happened to me. Anyway the fix in my case was the cable had a short in it. I called the place I got the scope from and they sent me a new cable. I think that Meade has problems with their cables. I have had the same problems with other Meade cables.

Subject: LX200 Tracking Problem Solution--Metal Chips in RA  

From: Doc G, Date: Mar 2001

The attached message is important for all LX owners. I have taken three of the RA assemblies apart over the last two years and noticed a chip or two in the base. But I recently had another base that I took apart again recently for a total rebuild. Astonishingly there were not just a few chips, but a lot of chips in the grease.

These seem to migrate from somewhere in the housing. The base should be taken completely apart and totally cleaned and degreased. Then relubricated. While the attached post says the worm is cutting the main gear, I find that hard to believe. Almost all worm/worm wheel combinations are made of a stainless worm with a wheel made of aluminum or brass. Both are soft. If the gears are clean in the first place and then lubricated properly, There should be no additional wear. That is not to say that one should watch for wear.

The speeds and forces on the LX gear system are very low so they should last forever. However, and I emphasize, they have to be clean a free of chips and other dirt in the first place.

I am sorry now that I did not emphasize this two years ago. I was under the impression that a chip or two was unusual. Unfortunately it seems lots of chips is normal.

Subject: RA Disassembly Procedure  

From: Doc G

> Kevin Macey <kmaceymediaone.net> wrote:
> Doc G., I have read many of your articles and postings and thought that you
> may be aware of any articles or procedures for the complete
> disassembly of the R.A. mechanism on the Meade LX series of scopes.
>
> I am working on several modifications to the drive and need to drill
> and tap several holes into the RA axis components. I am afraid that
> I will get metal shavings into the internals and would like to
> disassemble the drive to prevent this.

But of course you have asked the right person. :-) I have had the base completely apart. There is one tiny screw that holds the fork mounting structure onto the base. That does not mean it is easy to get the forks off of the base. The procedure is not for the faint of heart.

First remove the forks from the fork mounting structure. (For short I will call this piece the FMS) The FMS rotates with respect to the base and is held to the base with two rather large bearings. The fit is very good and quite tight, as it must be for smooth RA motion.

To get it off you first remove the electronics completely. Then under the cover plate on the top of the FMS there is a large washer held by a tiny screw. Remove this. Now the FMS can be removed from the base. It is generally very tight, but held only by the friction of the parts against the bearings.

The easiest way to get it apart is to tip the base on its side on a towel so it does not slide around easily. Then take a short piece of 3/4 inch wooden dowel and a hammer and tap the worm wheel from the bottom. If you tap it firmly and turn the FMS with respect to the base, you can little by little force the two parts apart. Be sure to tap it firmly an all around the edge so it does not jam crooked.

Suddenly, the two pieces will fall apart as the bearings release the parts. You put it together in the same way, by tapping the parts about the edges until the assembly slips together.

I found the base full of machining chips of all sorts on the two that I disassembled. A rather disturbing event.

Also, I have a series of 8 photos of the Base of the LX200 disassembled. These are raw jpg files. They are all together rather large being a total of 4 Meg. If you want these pictures please contact me privately and I will send them to you. I have also prepared a reduced resolution set which is 500K. Please state if you want the high resolution set or the low resolution set.

Subject: RA Motor (Classic) Problem Erratic Slewing -- FIXED  

From: Tim Long <Timtigranetworks.co.uk> Date: Dec 2005

Just reporting back on my RA motor problem, in case anyone else has a similar experience. My RA drive is now working again and all that was required is adjustment of the two variable resistors on the motor assembly PCB. It is a simple and painless adjustment but does require access to an oscilloscope.

The symptoms began as erratic slewing in ACP - sometimes the slew would not start and ACP would freeze waiting for a slew that never happens. In the process of troubleshooting the drive began making a strange clack-clack-clak-clak sound during the power on self-test, and I noticed that if I slewed away 10 degrees and back 10 degrees, the return slew would only make about 8 degrees of movement. I also noticed that the motor was having little spasms while searching for the home reference and that is what was causing the clacking sounds.

The cause of this problem is that the quadrature encoder circuitry deteriorates over time. The controller expects a square wave with equal mark:space ratio and the two signals should be offset 90 degrees in phase. The signal coming out of the motor is actually a sinusoid which gets converted to a square wave by a comparator. The sinusoid outputs can be checked by attaching an oscilloscope to the 3-pin test header on the encoder PCB - pins 1 & 2 are the outputs and pin 3 is ground. The variable resistors on the motor PCB adjust the comparator threshold and hence affect the mark:space ratio of the square wave. It seems that over time the adjustment drifts and the square wave deteriorates until it gets to the point where the controller can no longer determine the direction of the motor, whereupon operation becomes very erratic.

Solution: attach oscilloscope and adjust the resistors until both signals have a nice even square wave output. Simple in theory but complicated in practice. It is easiest to remove the motor to make the adjustments unless you can make or obtain a special tool that will fit into the cramped space. Another complication is that the circuit diagrams available from Telescope Service are incorrect. In their diagrams, they show a 6-pin connector (instead of the actual 7 pin connector) and the pin numbering is incorrect. However, on the TS diagram, there is an inset drawing of the encoder PCB showing the position of the encoder outputs and that diagram is correct - so the wires can be traced from that point back to the connector on the main PCB, where it is easier to attach the oscilloscope. Once the signal is clean, the motor can be refitted.

Thanks to Brian Bond for his troubleshooting tips and to TelescopeService.com for their circuit diagrams.

Subject: RA Slewing Overshooting Problem --part 1 of 2  

From: Rod Cook <cookrodgurulink.com> Date: Apr 2003

Bruce Gillespie wrote:
>The problem is my 10" LX200 'Classic' overshoots whilst on the Right
>Accession axis after slewing to an object, but, get this, only when
>moving counter clockwise.
>I managed to repeat the problem, and as we often say in the computer
>world, if you can replicate a problem, you have practically solved it.
>
>Here's what happens: Slewing counter clockwise via a GOTO to Jupiter
>from Saturn (I am 26 Deg South), the 'scope will swing past Jupiter
>about 30 degrees. Moving between these objects involve about 300 degrees
>RA movement. Once moved back clockwise to Jupiter via the keypad, the
>Declination is fine, and a Sync sorts out the tracking. Then slew to
>Saturn (clockwise movement of the RA axis) and it lands spot on
>Saturn, no overshoot. Slew back to Counter Clockwise to Jupiter, same
>problem (about 30 degrees overshoot on the RA).

I had a problem on my scope that showed up as a tracking problem which is not the same as what you're experiencing, but I think could possibly cause problems as you are experiencing. The problem was caused by loose opto-dectectors in the gearbox of the RA drive. The system uses LEDs and opto-detectors in the gearbox to generate pulses that are interpreted by the system as rotation direction and angular movement of the axis. Bruce Johnson has prepared an excellent discussion on how all this works....should be able to find the link in the archives. On my scope I found the glue that holds the detectors (which look like clear LEDs) had loosened and they were partially withdrawn from the hole in the gear box on the RA drive. I also checked the Dec drive and found the also loose but they had not yet caused a problem on this drive. I have re-glued the Dec drive detectors in place since this drive is easy to remove. But I have not removed the RA drive. I have wedged a piece of foam between the gearbox and the case to hold the detectors in place. Have not had any problems since. Someday when (if) I have a good reason to dismount my scope from the wedge, I'll fix the RA drive.

The are discussions in the archives how to get to the DEC drive. Very easy to do. To see the RA drive you need to remove the front panel of the base. There are also discussions in the archives about doing this. You will see the RA drive gearbox behind the control panel. Strongly recommend you read Mr Johnsons write-up first so you know what you are looking at. Be gentle when working with the opto-detectors or LEDs to avoid stressing the leads from the devices.

----------------------------------------------------------

Subject: RA Slewing Overshooting Problem --part 2 of 2

From: Tim Prowten <TimTelescopeService.com>

Bruce, he only thing I can think of that could cause this symptom is a problem with the opto feedback circuit on the R.A. motor assembly. The optos provide two pulse trains in quadrature which are monitored by the microprocessor on the main board. One pulse leads the other in time depending on which way you are slewing. If you are overshooting that means there may be too few pulses from one of the optos. In other words the microprocessor has to slew further to get the correct number of pulses for the calculated move. I believe the microprocessor selects the leading pulse train to count, so if one is producing too few pulses you would get asymmetrical behavior from the motor. The opto feedback circuits are adjustable so you should be able to tweak them to work correctly.

Subject: Description, Analysis, and Repair of Classic Dec & RA Drives URL  

From: Bruce Johnson

I've prepared a detailed description, analysis, and repair procedures for the Dec & RA drives at:

   <http://www.mapug-astronomy.net/ccdastro/decfix.htm> Note: should open a new browser window.

Subject: RA Drive Binding Problem  

From: Bruce Johnston Date: Feb 2004

-------Original Message----------
Tom <stoneflycomcast.net> writes:
I have a used LX200 Classic in 8". The scope was missing cords, finder, hand controller, etc. After hunting down parts and setting up the scope, everything works fine except for the RA drive (azimuth). Using the hand controller, the drive will not move through a full 360 degrees. After about 90 degrees the drive starts to labor, slows down and eventually stops. Unlocking the scope and returning it to zero (with the lock and fine adjustment knob facing the electronic control panel) and then using the hand controller starts the RA drive moving again, but it then labors and stalls at about the same position.

Similar results occur in GOTO mode, where the Dec moves fine but the RA will move to the same approximate location and bog down and then stop.
-------End of Original Message----------

Tom, you've been given some good ideas to check out, so I'll just add a bit to them. No matter what the problem is, you'll have to take the bottom off of the scope so as to get to the RA drive mechanics. This is no big deal, though.

Now, when you get in there, look for the foreign objects in the grease as has been mentioned. But if all looks well, what you want to do is to run the scope in RA while you're looking in from the bottom and the scope laying down. Just run it at a relatively slow speed of slew and let it go until it begins to bog down for you. (You can have the RA clutch disengaged during this so that the scope won't try to turn on you.)

When you get to that spot, assuming you haven't already seen what the cause of the bind is already, then put your finger on the gearbox and lightly push it so that the worm moves away from the worm gear. It should move about 1/8" or so, but it definitely should be able to be moved.

If you find that you can't get some clearance between the worm and worm gear, then this is the cause of the bind; they're meshed too tightly. There is a set screw that screws in from the bottom of the unit, that pushes the worm assembly up toward the worm gear. If the screw has been adjusted too tightly, it causes the worm not to move away.

The whole purpose of this set screw is to allow for some movement, but not to allow the worm and worm gear from ever completely disengaging. The person you got this from just may have tightened the set screw too tightly. It's not uncommon at all for people to adjust this screw and end up making it too tight. They've perhaps adjusted it because the gears were truly beginning to unmesh, but went too far. Then, with the temperature change between places where the scope was used... or whatever... the adjustment is now too tight. If so, then again, adjust it so that you can get a max of about 1/8" of movement between the worm and worm gear.

If the person you got the scope from has replaced the RA drive and had problems with it, then called Meade, they will have suggested that he make this adjustment because of excess gear slop. As I say, it's not uncommon for this person to get a bit too ambitious go a bit too far and make it too tight.

Just another thing to add to your possible causes. But don't get too concerned. There have been many people over time that have had your symptoms, and almost always, one of the suggestions you've received has fixed it.

Subject: LX200 Base Construction & Limitations  

From: Doc G, Date: Jan 2004

I have now taken the base apart to the point of removing the insert in the bottom of the cone. This insert is threaded into the bottom of the cone from the bottom. The cone holding the bearings is a part of the base casting and has at the base of the cone a threaded opening which takes a threaded part that has a center thread for the 1/2" -13 rod from the tripod mounting bolt.

I can now assure that the cone assembly including the threaded insert is exceedingly strong and free of any flexure that I can detect. Thus I doubt that an additional threaded bolt going from the top of the cone to the wedge below will have a significant effect on the strength of the entire structure. I can still recommend that a center bolt be used with the wedge. This has, I understand, been done with the new 14" LX200 GPS. It seems wise to use this same technique with the other LX200 scopes. The modification is very simple since only one hole need be drilled into the wedge and a 1/2-13 bolt installed.

With this post on the design of the base, I am essentially through with analysis of the base design. The springiness of the forks has, in my opinion, been tracked down to the bearings and the fact that these bearing are too close together. There is no simple modification that can "fix" this problem. It is a problem that is inherent in the Meade design of the base of the LX200. I believe that Meade has done the best they could with the base of the LX scopes. Their fork design has set a standard for what a fork mount should look like. And, unfortunately, a standard for the quality that can be expected from this design. It is too bad that his design has received such poor results and gleaned a bad reputation for fork designs over the years. A fork design is actually quite capable when done correctly.

To see a design that works well, you have to go to the Mountain instruments site. It is actually the Mathis Instruments site. See it here:
<http://www.mathis-instruments.com/>

As you will see at that site, the solution to the instability of the fork mount requires an extended RA axis which allows the bearings to be placed further apart. This is an obvious solution, but I know of no other designers, than Mathis Instruments, that do this correctly. I recall that there were several others, but I have lost the references. Perhaps one was Optic Craft. If there are others I would be happy to have the references. I am personally pursuing getting a fork mount from Mathis Instruments.

This will be my last post on the LX 200 base design. I am convinced that within the package profile that Meade uses, insists on, there is no way to fix the problems with an unstable RA axis. And, there is, in my opinion, nothing more to say about the Meade design. It has been an interesting journey.

Subject: Removing Lower RA Bearing --part 1 of 3  

From: Bruce Johnson Date: Sept 2001

Doc G writes:
<< I think you will find driving the bearing out is easiest from the bottom after you take the electronics out. Normally they are not that tight. Use a torch on the thing if necessary. That helps a lot and will not warp anything. These aluminum castings are massive and tough. But don't burn the paint off of it. That is too hot.>>

Driving it FROM the bottom?? Sorry, Doc, but I must be missing something here! The bearing appears to be pressed IN to place from the bottom! I can't see any way of driving the bearing out, except to come in from the top of the cone, where the upper bearing is, and driving the bearing down, toward the bottom. Am I looking at something wrong here?

Update: I got the lower bearing out! I just heated the housing holding the bearing with a torch for around 10 minutes until it got hot to the touch, then tapped on it with a cutoff piece of broom stick handle, through the opening that the upper bearing sits in, and that did it. Thanks to all that responded.

The numbers on the bearings are:
For the upper one, my replacement bearing says: SR-20 and that's all. The lower one has 6013-2RS1 stamped on it. Here is at least ONE place where you can get the bearings online if you wish. It's where I ended up getting mine.

  <http://www.arrowweb.com/bake/home.htm>
   Bearings by Johnson Bearing and Industrial Supplies.

Be advised, though, that the owner of the company is going to probably suggest to you that you not replace them, but rather, remove the rubber seal on the side and wash out the old grease, then re-pack it with new grease, He very strongly recommends a Teflon based grease.

Both the owner of Johnson Bearings and also a local bearing supply house say that when it comes to 'precision', none of it applies to the application as we use the bearings. That only applies to how well the balls in the bearings respond under extremely high speeds or very high temperatures or both. That using the lowest grade of bearing will have no effect compared to using the most expensive, 'precision' bearing.

-----------------------------------

Subject: Removing Lower RA Bearing --part 2  

From: Doc G

Well, now I do not understand. There are some pictures on my web site about this. But in words, you first take off the cover plate on the fork. Then you remove I screw and take of the fender washer. Then you go into the bottom and tap against the gear mounting plate until the base comes off. The two bearings will come off at the same time. It is wise to take them off at the same time so that the bearings do not get jammed.

See the photos on my website at Mechanical Analysis.

-----------------------------------

Subject: Removing Lower RA Bearing --part 3 of 3  

From: Bruce Johnson

Okay, Doc, I think the problem perhaps was in my terminology. If we use your upper left picture on your page, we see that the lower RA bearing is still mounted on the lower section, with its inner race resting on the 'cone'. However, you can also see that when the lower section is joined to the upper section, the outer race of the bearing will slide into a 'ring' that is just below the RA gear, and that ring is in the upper section.

In my case, when the upper and lower sections were separated, my lower RA bearing did NOT stay on the 'cone', but instead, the outer race was snugly held in the 'ring' below the gear. It was a very tight fit, in fact. The only way to get the bearing out of that 'ring' in the upper section, was to come down through the opening for the upper bearing and tap the lower bearing down. That forced it out of the 'ring'.

However, my bearing was so tight that I had to heat the 'ring' to make it expand a little, so as to allow it to come free when tapped from above.

Apparently, it is most common for the bearing to stay stuck to the 'cone', based on what happened with Scott, and other feedback I got offline. My situation was just the reverse. I think that the reason for the difference is, when I last had the two units separated, I made sure that the entire 'cone' in the lower section was well greased, so that the units would more easily slide together. That helped keep the lower bearing from seizing on the cone.

Tomorrow, when I install the new lower bearing, I'll not only lubricate the inner race, but the outer one as well, and it should slide into the 'ring' much easier than it came out. Also, for the past few days, my bearing has been in my freezer so as to shrink it a little, and that should make it slide into the ring even easier. But before I join the upper and lower units, I'll first let the bearing warm up, so as to not be tighter than necessary on the inner race to the cone.

I hope this makes sense, and explains why I had to come in from the top unit to get the bearing free.

Subject: Replacing LX200 Worm Gear Spring  

From: Bruce Johnston Date: May 2001

I've replaced that spring in my own scope, and once a person can get past the 'fear factor' of digging into the scope, it's really not bad at all.

One has to remember that many of the issues facing the Dec drive, such as retrograde motion, backlash compensation, etc. aren't significant factors for the RA drive, so there's a lot more latitude in what a person can do without negative effects.

Just remove the RA gearbox and worm assembly by removing the two Allen screws, then unplugging the connector from the RA assembly where it plugs into the main board. You're taking if fully out, only to give yourself some room to look at it comfortably. You don't really have to unplug it if you don't want to. You should, however, unplug the ribbon cable that is coming from the control panel to the main board, just to give yourself plenty of room. (This may sound scary the first time, but actually, you'll see there's nothing to it.)

When you have the gearbox out, you'll see that you can just lift the spring out from between the two plates holding it. One end sits down into a small recess to help keep it in place when you put it back together.

Take the spring to your local hardware and find a spring that's about the same diameter, but a bit stiffer. If not stiffer, then perhaps just a little longer. You very well may have to buy a somewhat longer spring and cut it to the necessary length to get the desired tension. The idea is to find one that you can put in the originals place but with maybe 50% more tension or so. Pop that spring in, in place of the original .... the recess in one of the plates helps in holding it in place for you... and put the assembly back in. Wiggle the assembly and check for the original sloppiness. If it's quite a bit better, you're probably all set. If not, cut a little longer section of spring, or get a somewhat stiffer spring, and try again.

Put the gearbox back in, plug the gear drive connector and the ribbon cable back to the main board and you should be ready for a live test.

Just keep in the back of your mind that this isn't brain surgery, and don't be afraid of messing up. That's why you kept the original spring in original shape!

Subject: Mod for Adjusting the LX200 RA Worm Spring   

From: Bruce Johnston Date: Nov 2001

I just put a new drawing at the end of my 'dec fix' writeup. It's nothing to get excited about, but perhaps others might want to add it, or the other change with it, when they have their LX200 base plate off. It allows for adjusting the spring tension on the drive assembly without having to remove the base plate in the future.

Rather than have to go through the entire writeup on Dec and RA repair, you can just jump to the last page by going to the following address: <http://www.mapug-astronomy.net/ccdastro/decfix_9.htm>

Subject: Removing Dec/RA Motor Clutch Plates   

From: Ray Wallace <raywallacealtavista.com> Date: Nov 2001

I have done the Dec. axis bearing mod. as suggested by the Mapug Topical Archive. I had a hard time getting the screws off that secure the back clutch plate to the Dec.., too. I tried heating them with no luck. The Allen wrench stripped the holes. I finally used a drill to take the flat head off the screws. I did discover an easy way to break the seal caused by the glue that was used. I used a small claw hammer that was small enough to slide the claw into the space between the side of the clutch plate and the side of the fork arm housing. Rest the claw against the back of the clutch plate and the hammer head against the back of the fork housing. I found an easy, but firm tap on the end of the hammer handle was sufficient to free the clutch plate and slide it off. The remaining screw studs were easily removed using a pair of vice-grip pliers.

Subject: Bias Weighing the OTA Fork Arms vs. Elastic Pulling  

From: Bruce Johnston Date: Dec 2001

I thought I'd pass along a little trick that I brewed up recently. As many of you know, it is suggested that the forks be weighted somewhat to one direction, so that the East side has more weight, thus making the RA drive 'pull' the scope against some resistance. There are several reasons for this.

The bad part about just putting some kind of weight on the Eastern fork, is that the only time when that particular weight is having full effect is when the scope is aimed pretty near your meridian. As the scope is aimed more easterly or westerly, the effect of the weight diminishes, and when aimed truly East or West, the effect has completely disappeared.

What I did for my pier mounted scope was to first balance the scope with a weight until it was nicely balanced East/West. Then I grabbed a square, hollow metal bar that I had around here. It's about one inch per side, and about 18 inches long. (Remember; I used that size only because I happened to have one left over from some other experiments.)

I took the bar and shoved it beneath the plate on top of my pier, between the pier and the plate, with the bar running East to West. This isn't a tight fit or anything. It just sits there, very loose.

Next, I went to a sporting goods store and bought an inexpensive mechanical fish scale and then went to the local merchandise store and bought a strip of elastic about two feet long. Cost so far, about $4.00.

Next, I cut a piece of the elastic from the strip, attached one end to the fish scale and the other end to the Eastern fork arm. I took the remaining piece of elastic and connected to the other end of the fish scale, then wrapped it around the bar under the plate on the pier. I now am set.

When I aim at an object to take an image, I just rotate the bar to either take up more or less of the elastic, until I get a reading on the fish scale of about two pounds. It doesn't matter what direction I'm aimed; I still set it for two pounds or thereabouts. The forks are now nicely balanced with a weight to the East of about 2 pounds. Approximately every 30 minutes or so, I check the fish scale, and if necessary, I just rotate the square bar to set the pressure of the elastic on the fish scales for the proper reading.

If it turns out that I want to aim quite a bit to the East, I simply connect the elastic to the Western end of the rod instead of the Eastern one and I have lots of room for the elastic to do its job. Nice and easy. Keeps the weight correct for all angles of the sky.

As a side point, I also experimented quite a bit with pulling on the WESTERN side of the scope when aimed West. In *MY* experiences, there was absolutely NO difference in the tracking of the scope! I got exactly the same FWHM on my stars in an image regardless if I had the elastic set so that it tends to 'pull' the scope, or if it 'retards' the scope drive. For me, at least, some evidence that the idea of loading the scope Easterly only, is potentially a myth.

Needless to say, this idea isn't limited to pier mounted scopes at all. You simply need to find a spot on your tripod where the elastic can be attached or tied. BE SURE TO DISCONNECT BEFORE SLEWING!

I keep forgetting to specify that my scope is a 10" F/6.3 LX200. For this particular scope, assuming it isn't overloaded, loading it to the East (or West) has some merit. However, if it IS overloaded, then perhaps a person should consider the elastic mounted so that it 'pulls' the scope West. Might just help reduce the load a bit.

Also, the elastic idea wasn't suggested to be used in all cases. It was suggested as an alternative to an existing scope that is loaded with weights to the East. One has to use reasonable judgement when they go about doing ANYTHING that is outside the basic recommendations of the manufacturer.

Subject: Imbalance for Better RA Tracking  

From: Roger Hamlett <ttelmahntlworld.com> Date: Mar 2002

----- Original Message 1 -----
> From: Darren Carlisle <darrencarlislehotmail.com>
> I've now seen many posts on accurate balancing of the LX200 and I've also
> seen a few that say you should slightly over weight one end, this is to keep
> the tension on the gears, so they say.
> My question is what is right and what is wrong. I can see the advantage of
> having one end heavier than the other but by how much for a 10" LX200.

----- Original Message 2 -----
From: Giancarlo Podio <jats_wshotmail.com>
> I too have read those suggestions in the past and adopted them with good
> results. I have imbalanced my scope just enough so that when the clutch is
> loose the RA axis slowly rotates counter clockwise. This obviously is with a
> wedge, I'm not sure if the same would help for an AltAz setup. The ideal is
> to have the weight pulling the scope slightly against the rotation of the RA
> axis, this allows the RA gears to "push" the scope around it's axis and
> letting the off balanced weight act as a means of ensuring constant contact
> between on side of the worm gears. It's actually easier to test it for
> yourself than to explain it. Try to imbalance, for example, your scope in
> it's DEC axis, now turn the worm gear in both directions and you will find
> that one direction is smoother than the other, typically the one acting
> against the force of the out of balance weight. I'm not sure if the
> advantages would be the same for the DEC axis as this is used in both
> directions when correcting during guiding, whereas the RA gear is only used
> in one direction.

Imagine that you have a scope 'perfectly balanced' in all axes. This is motorised, and tracking in RA. Now the first potential problem, is that with no 'weight' on the gears at all, if something does 'nudge' the scope a little, it can move away from the actual driving surface, by up to the amount of backlash in that drive. It will then sit still, and wait for the drive to 'catch up'. If instead it is _slightly_ loaded (and the emphasis on this imbalance is 'slight' - only an ounce or so is needed), then it will when released, move slowly back and engage on the drive surface again.

In the Dec direction, if it is disturbed, there is nothing at all to make it move back. Now if you then have a 'control' system, that involves adjusting the RA speed, and assume that this is like the system on the LX200, which actually 'stops' the drive for a moment, when asked to adjust east. When stopped, all the load comes off the gears. Unfortunately, when you restart, this can result in a little 'shudder' as the gear once more becomes engaged.

With a slight imbalance, this doesn't occur. Having a slight 'preload' on gears, is a standard method of reducing the effects of backlash. However you want to keep the loading as small as possible, to avoid too much loading on the drives. It is rare for a scope to really be 'perfectly' balanced (the stiffness of the bearings, makes it almost impossible to 'find' this point), so a small load is normal. Since the RA axis tracks in only one direction for normal use, it is preferable (as said above) for this load to be on the eastern side. Ideally, what is needed is a light spiral 'spring', imposing a small (and nearly constant) torque on the gears, but failing this, the careful application of a small load is the best method.

The comment about unbalancing by 'just enough so that when the clutch is loose the RA axis slowly rotates counter clockwise', is spot on. Applying too much imbalance creates unnecessary loads on the drives.

Subject: RA Setting Circle Use   

From: Jon Brewster <jon_brewsterhp.com> Date: Dec 2001

> I am learning to use the LX200 in polar mode and just got the wedge
> installed. I have a question concerning the RA scale: the
> manual is rather coarse about it and says:
> "The R.A. Setting Circle has two sets of numbers,
> the inner set is for Southern hemisphere use, while the other is for
> Northern hemisphere use."

I did a lot of fiddling with RA circle. Outer is definitely for Northern observers. You can get a write up of some of the things you can do with the circle at:
<http://www.proaxis.com/~sandstone/Astro/ProcDuring.htm#Circles>

Subject: Loose RA Motor?  

From: Bruce Johnston Date: Nov 2001

Paul writes:
<< My LX200 12" is about 6 months old. Over the last few nights I've had
trouble keeping on target. This AM in the light of day, I noticed that with
the RA locked that I can move the entire fork and OTA assembly about the RA
axis 4 or 5 degrees. The knob does not turn. (Of course I tried to adjust
the knob and the resulting pain of getting it back on) Is it a "send back to Meade" job? >>

That can be caused by several different things, but all of them have to do with the RA worm assembly. The first thing is, the two screws holding the gearbox/worm in place may be loose. Also, if the spring on the RA gearbox that pushes the worm into the worm wheel is too weak, it can allow for that movement. Those are two of the more common causes, but there are others as well.

You can pretty much spot what it is by laying the scope on its side, remove the bottom plate of the scope, then lock the lock. Now, while wiggling the upper assembly back and forth, as you do to get the movement, look inside at the worm and worm wheel. You should easily now see what is moving and what isn't.

If you've never had the bottom of your scope off, it may sound complicated, but it's not. Just a few screws holding it in. Don't forget to take out the two screws in the middle that also hold it in. They hold the bottom plate to a heat sink, so be sure they go back in when you're done. There are two screws also in the middle that DON'T need to come out, but you can spot them by the fact that the bottom plate has small holes that go around these screws and obviously the plate isn't under them.

Subject: LX200: Atmospheric Refraction Adjustment-- part 1 of 2   

From: Doc G, Date: Feb 2002

> John Briggs wrote:
> I've just joined MAPUG, with a specific technical question. I'm
> using seven 12" LX200s for a solar observatory site survey, and
> the observations require solar tracking starting very soon after
> sunrise. Consequently, I have early morning tracking errors due to
> atmospheric refraction. While the mean solar rate for an LX200 is
> 60.0, this rate is good only near the meridian (i.e., near local
> noon). Near the horizon, the tracking rate must be considerably slower.
>
> Our instrument has an autoguider for declination tracking, but for
> various technical reasons, autoguiding in RA is harder for us, and we
> have not implemented it (yet).
>
> As I understand, the LX200 corrects for refraction during
> POINTING, but not in an ongoing way during TRACKING. (Some telescope
> control systems, such as Dave Harvey's COMSOFT TCS, correct for
> differential refraction during tracking -- a nice feature.)
>
> Thus, we're presently stuck with marginal tracking in RA, given
> that we want our instrument to require a minimum of human attention
> over the course of a day. Our solution has been a
> refraction-compensated look-up table, which is communicated to the
> LX200 via a serial line from a support computer. Every hour, a new
> solar rate is communicated to the Meade. This works OK, but not as
> well as we'd like. (We may have to correct more often near the
> horizon, for example.) Our goal is solar tracking +/- about 100
> arcseconds in RA, starting shortly after sunrise and lasting till
> about 4:00 PM. (As I said, declination is already corrected via
> autoguiding and isn't a problem.)
> If anyone has experience that may relate to these issues -- I'll
> be glad to hear from you! Meanwhile, we've begun work on an RA solar
> autoguider (but we're not looking forward to it!).

I am somewhat familiar with the LX200 electronics and offer a few comments and suggestions in the following.

Sending a new clock rate each hour must be incorrect. In the first hour the sun would be well out of the atmospheric aberration region. Perhaps you meant a new rate each minute. But whatever, this is not a good way to control the tracking rate of the LX 200. The problem is that a clock command very likely requires the down counter to resent and this introduces a glitch in the RA rate. The electronics is not designed to control the RA rate in this way.

The electronics is designed, very nicely in fact, to control the effective rate by stopping the RA drive or speeding it up by a factor of 2. This commend can be applied several times per second. Thus, if you want to slow the RA rate, you send short, successive East commands to the electronics. If you stop the drive for a fraction of the time you effectively slow down the RA rate. This can be done very often so that the effect is smooth rate control.

The East command can be sent through the serial connection which you are already using or it can be sent through the CCD socket. The CCD socket is standard TTL 0 to function. Using the serial connection simply requires that you use the appropriate control command for any serial port drive like Visual Basic. (or whatever you are running)

Using the CCD socket would require a second serial port using an appropriate command program. This would be a bit more complex to implement but would have the advantage of running independently of the other programs you might be using.

I hope these hints are of some value to you. It sounds easy on paper. I do not have the atmospheric data at hand to actually implement this, but I sense that this would be relatively easy to do.

----------------------------------------------------------

Subject: LX200: Atmospheric Refraction Adjustment-- part 2 of 2   

From: John Oliver

Small addition to Doc's good advice. I regularly control external devices using my otherwise unused second parallel port and software written in VB6. You could send commands to the CCD port this way I think. I have VB code that calculates the sun's altitude that I can probably provide (I don't think I used any proprietary routines) and the refraction correction would be easy to add. You could have a small compiled app that would pulse the CCD port as needed to correct your tracking.