David's Astronomy Pages
Notes - Session 598.1 (2016-12-27)

2016-11-23 to 2016-12-29
Bullet LX200 - Main Board Failure (2016-11-23)
Bullet LX200 - New Main Board (2016-12-19)
Bullet LX200 - Observatory Testing, Various Issues (2016-12-20)
Bullet LX200 - RA Drive Diagnostics (2016-12-22 to 2016-12-27)
Bullet LX200 - RA Worm Drive Tension Spring Adjustment (2016-12-29)
Bullet LX200 - Declination Knob Removal (2016-12-29)
Bullet LX200 - Autostar II Settings
Bullet LX200 - Autostar II, Firmware Update to 4.2G
 
Bullet Images from 2016-12-27 >>

LX200 - Main Board Failure (2016-11-23)

Imaging session attempted with 12" LX200R on 2016-11-23 following a long layoff.   Attempts to power-up the LX200 failed completely (no red light on panel, no response from handbox display, no sounds from scope/mount apart from faintest of clicks in the handset when power was initially switched on).  The power adapter supplying the LX200 appeared ok as it showed usual green light when powered on.

This all suggested that there was a serious problem with the telescope mount.  A nearby lightning strike back in July had taken out the house's router, and it was suspected that a power surge or ground currents had probably killed the main board in the LX200's mount. The scope was removed from the equatorial wedge and brought indoors (the scope could in fact have been left on its wedge

During the following days I identified the best course of action was to remove the Front Panel/Main Board and send it and the handbox off to "SC Telescopes" in Kent for examination by Steve Collingwood - a Meade repairs specialist (this being a better option that shipping off the entire scope, with the high shipping costs entailed).

Pictures where taken of the main board before its removal on 2016-11-28 to show the position of the various leads (as a check for when new board was installed at a later date). 

The report came back on 2016-12-08 that the main board had indeed failed and couldn't be resurrected, but the handbox was ok. 
I choose to have a new main board ordered from Meade for a cost of 330.   The new board arrived on 2016-12-14, with the old handbox arriving back a day later.

Lead attachments before removal of old board
 Image  Image
  

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LX200 - New Main Board (2016-12-18)

The new main board was installed into base of the LX200 mount on 2016-12-18. It was confirmed that the LX200 powered up and initialised ok, and that controls could move the scope in RA.

New Front Board
Image  Image
  

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LX200 - Observatory Testing, Various Issues (2016-12-20)

The scope was moved back to the Observatory and placed on its equatorial mount. Various leads were then reconnected.
Various tests where made using Autostar II handbox and via connection to laptop running TheSky6, during which a series of issues/problems were encountered. 

Autoguiding Port
Immediately an issue was noticed when the autoguider cable was pushed into the Autoguider port on the New Panel. The port was completely lose in it slot in the new panel, such that when the cable was inserted, the port and the main board pushed away from the Front Panel (apparently this is a problem with new panels coming from Meade recently).   A similar issue was also noted with the RS-232 port, but being better supported it didn't push in as far as the Autoguiding Port. Later on the issue was fixed by removing the Front Panel to access and glue the Autoguider Port and two RS-232 Ports into their respective slots in the Front Panel.

USB-Serial Connector
The next issue surfaced whilst attempting to make a connection between laptop and the LX200, via TheSky6 and USB-Serial adapter/RS-232 cable. I simply couldn't get a successful connection.   Tried a different USB port, restarted the laptop etc. I tried updating driver the USB-Serial adapter, but it was already the correct one. Despite that I reinstalled current latest drivers from the manufacturer for the Prolific chip in the adapter using their installation program, but still couldn’t connect.

I eventually resolved the issue by swapping the USB-Serial adapter out for another Prolific adapter than I was previously using with a Cloud Sensor. Using this alternate adapter I was finally able to make the necessary connection to the LX200 scope from my laptop.

It is asummed that the old adapter was compromised by the same power surge that messed up the Meade main board on the LX200. The effect on the USB-serial adapter was subtle as the ‘old’ adapter appears to function ok when I then used it with my Cloud Sensor. To make sure it wasn’t me. I re-tried it with the scope, but again it wouldn’t work. Not sure why, but I suspect the adapter stopped performing 2 way communication, necessary for the Laptop/LX200 Comms.  However it still performs 1 way communication and was able to read regular sensor outputs from the Cloud Sensor. The effect on the house router was similarly subtle, such that LAN cable and wifi access still worked, but the surge just totally stopped it from being able to get broadband connection outside of the house anymore.

RA Drive
Whilst testing the motion of the scope in RA it was noticed that a fairly lound clattering sound when slewing in a clockwise direction. There was a similar sound when slewing in anticlockwise direction, but it occurred over a different RA range. I didn't remember hearing such a clattering sound before and when the scope was last in use in Spring 2016.

The sounds were concerning enough that they needed to be investigated and fixed beforethe Observatory could be properly used again.   Although there was potential for causing further damage (if it was indeed damaged), it seemed appropriate too carry out a series of diagnostics tests with the scope mounted in the observatory,  whilst reading up various information resources and forums online.

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LX200 - RA Drive Diagnostics (2016-12-22 to 2016-12-27)

A series of tests where conducted to try to identify the likely source of the RA drive problem. 

Timing of Clicks 

By reducing the slew speed down to 1.5 and then 0.25 arcdeg/sec it became possible to identify that the clackety-clack sounds when driven at 5 arc deg/sec were actually comprised of a series of regular clicks. Counting the number of clicks in a given time and equating this with the slew speed it could be shown and the clicks occurred approximately every 0.22 turn of the worm gear.    An sidereal tracking speed the clicks occur every 105 seconds or so (i.e. approximately every 1m 45s). 

It didn't appear that a damaged or broken tooth in the gear train (or damage to two teeth on touching gears) could explain these 105 seconds clicks (assuming either LX200 Classic or LX200GPS gear ratios). The clicking would have to be either much faster or a bit slower.

Later visual examination of gears didn't show any damage to the teeth on the visible brass gears or any damage to the worm drive or large RA gear beyond 'normal' wear. It was not possible to inspect gears within the gearbox sitting at the end of the RA Motor.

Occurance of Clicks versus hour angle.
Slewing the scope in RA all the way clockwise and all the way anti-clockwise  showed that the issue was not present across the full 360 degrees of rotation, but was resticted to certain sections of rotation with the peak problem lying at certain positions.   The sections with issue for clockwise slewing and anticlockwise slewing where different, though not unrelated. Problem was worse for Clockwise Slewing.  This suggested that the weight of OTA, Forks and there balance played a factor in the problem. It is possible that a slightly ellipitical RA drive wheel may play a part.

Plot showing Hour Angle Zones where RA gear clicking can be heard
Zones with clicking are different for clockwise and anticlockwise slew. 
Zone arcs are shown thickest where the clicking is worst.

Image
Note : The above plot is for one particular balancing of the scope.
The gear clicking zones are noted to vary slightly depending on the
E/W balance of the scope, but they always have the same general pattern.


Impact of Clicks on Tracking
In addition to the potential for further damage to the RA drive, there was a signficant concern that RA tracking and thus AstroImaging would be seriously impacted by the RA drive issue.     

To understand the precise impact on tracking and to acquire further diagnostic data, a star close to Dec 0 was followed in PemPro  whilst tracking (with Pec Off).   The results showed the scope was being subjected to regular sharp shifts in RA position (~30-50 arc secs  jumps) with a period of approximately 104-105 seconds.  The jumps seemed to be preceeded by an interval of ?strain and followed by a period of ?relaxation.   The magntitude of the jump varied somewhat and sometimes wouldn't be present (like a skipped heartbeat).  As the period bears no relationship to the roughly 24 minute worm gear period (1436.07s to be precise the jumps can not be removed using PEC (periodic error correction) and furthermore compromises the quality of periodic error data that can be collected.

The normal fundamental frequences for a 12" LX200R(GPS) scope are
 478.69 (3x) - Worm Drive, Transfers Gears  ('3x' means '3 time per worm period')
 179.51 (8x) - Motorbox Gear 1
  71.80 (20x) - Motorbox Gear 2
  28.72 (50x) - Motorbox Gear 3
   9.57 (150x) - Motor


Examining a separate section of RA where the click sounds weren't evident showed a 'normal' periodic error trace with no signs of any RA errors with a 105sec period.


PemPro plot showing Tracking Errors in RA Drive (2016-12-27)
(plot shows very obvious regular spikes where the RA Drive in slipping)
Image
 
PemPro plot showing Frequency Specturm of the RA tracking data (2016-12-27)
The spikes / RA bumps that occur every 104-105s to do not correspond with
any of the known mount fundamentals for the 12" LX200R(GPS) scope.
The feature repeating every 52.4s can't be seen in the graphs of RA error, but it is noted that 52.4s
is approximately half of 104-105s.
Chart
 
Detailed view showing RA drive issues (2016-12-27)
(whilst the gear slips are regular, there is no correspondance with the
8 minute / 24 minute worm drive period and therefore
there is no way of removing the spikes in tracking using PEC)
Image
 
  PemPro plot showing Tracking Errors in RA Drive in a different part of the sky (2016-12-27)
(in this part of the sky there is no gear slippage and there is 'normal' Periodic Error)
Image

 
 

Impact of Clicks / Poor Tracking on Imaging
Attempts to image Abell 10 showed up the problem created by the RA jumps associated with the clicks.  The following 30sec frame shows the impact of a 50 arc sec jump in RA tracking, as the star shifts firstly one way and then the other. Only 4 out of 27 frames could be used for creating a Stacked Image (i.e. a 85% wastage factor)

  Impact of RA drive issue on Imaging
Image
 Annotated CCD Image (75% size)
30s exposure, 3x3 binning, C Filter
2016-12-27 22:57h UT (#598228)
12" LX200R  + ST-10XME
 
Image
 Annotated CCD Image (75% size)
30s exposure, 3x3 binning, C Filter
2016-12-27 23:02h UT (#598235)
12" LX200R  + ST-10XME

In addition to the errors produced by jumps in the scope's RA tracking every 105 seconds or so, there is also an overall RA drift of 2.3 arc sec/minute (varying from 1.76 and 3.46 arc sec/minute) with the scope tracking with an average at 99.74% of sidereal rate (i.e. 0.26% slower than sidereal).

  Plot showing RA drift across a 73 minute interval
Image


Diagnosis and Proposed Fix

It was suspected by now that the issue with the RA Drive and associated clicking was being caused by slippage of the RA worm drive against the main RA gear. 

A post by Christopher Erickson on the Cloudy Nights forum (http://www.cloudynights.com/topic/398945-sticky-wicket/) describes the issue well. The particular problem under discussion related to the Dec gear, but the author describes that the problem can also manifest in the RA worm drive.

It is called stiction and can be common in mounts with spring-loaded worm blocks.

It is when the worm gear spiral teeth ride up on one side of the worm wheel tooth grooves and suddenly pop back down to the bottom of the grooves when it hits the range-of-motion limits set in the spring loading mechanism. This process repeats rapidly and creates a chattering sound.

Replacing the worm drive tension-spring with a slightly-stronger spring and then adjusting the worm block spring range-of-play down to a minimum will help, as will making sure that the OTA is fairly-balanced.

This problem can also manifest in the RA worm drive and has the same solution

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LX200  - RA Worm Drive Tension Spring Adjustment (2016-12-29)

With the RA drive problem sufficiently understood the 12" LX200 scope was moved indoors and the base opened in order to access the RA drive.

Visible examination of the visible gears showed that there was no damage evident to the teeth on any of the gears that were in view (ie the 2 brass gears on side, the worm gear and the large RA gear).  This was as expected based on diagnostic tests. It was not possible to examine the gears inside the gearbox attached to the motor, but the problem was not believed to lie here based on the diagnotics data collected.

Tests involving lifting the RA drive unit from its spring tensioned position whilst the scope was being driven in RA demonstrated that it produced regular clicking like the sounds that came from the RA drive when it was being slewed (or was tracking) in certain RA positions when the scope was mounted on its equatorial wedge.  This confirmed that the RA worm gear were liable to slipping and that this could probably be remedied by increasing the spring tension that holds the worm gear against the large RA gear.

Quick examination located the spring that holds the RA drive unit (worm) against the large RA gear.   Lying at one end of the spring is a short bar which controls how much the tension spring is compressed (and thus controls the tension that holds the RA drive unit against the large RA gear).   After marking the initial position of the short bar, its bolt was loosened with an Allan key, and then repositioned in a way that compressed the spring to a greater amount (negating the need to acquire and insert a stronger spring which is the alternate solution).  A screw that limits the range of play of the worm block spring was then adjusted for the new position. 

Testing (initially indoors but subsequentially outdoors with the LX200 mounted on its equatorial wedge) showed that RA slippage problem appeared to be fixed and there was no further clicking sounds when the scope moved at normal tracking speed or was driven at slew speeds. 

Whilst clicking sounds and large RA jumps seem to have gone additional testing on 2017-01-02 involving tracking RA errors using PemPro 2.8, show the continued presence of smaller 10-13 arc sec bumps in RA every 104.2 secs.   (details here).  This is still of concern as these correspond to a non-integer number of cycles per worm period (i.e. 13.78 cycles) and I can't see how I can successfully eliminate this periodic error using PEC since the RA bumps on one period do not occur as the same phases as the bumps in subsequent periods. 

View with Base Removed (left), RA Motor & Gears (right)
Image  Image
 
RA Drive (left), RA tension spring (right)
Image  Image
  
  RA Worm & RA tension spring
(black mark shows old position of the spring tension control bolt,
before repositioning to increase spring tension)
Image
 


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LX200  - Declination Knob Removal (2016-12-29)

Whilst the scope was being fixed for the RA Drive Issue, I had opportunity to look at a problem with the Declination Knob (the one that allows manual manipulation of Dec).  When the scope is being slewed or other moved in Dec under either handbox or computer control, the Declination knob rotates rather violently and makes a louder noise than it should.

Examination showed the axle to be bent which causes unbalanced rotation of the heavy knob. The reason why the axle is bent at it enters the gear housing is unknown. Was it damaged at some point in past when the scope was being moved or transported?.  It would seem that quite a bit of force would be needed to bend the axle, and a corresponding large amount of force needed at just the right angle to get it back into any form of correct shape, if indeed it ever could. Since the manual knob is never used, but causes extra noise/vibration and might impact Dec movements, it was decided to undo the Declination cover & clutch to access the Declination block.  Undoing 3 small screws (allan keys) at the base of the manual gear unit and temporarily removing one of the small brass Dec gears allowed the Declination Knob/Axle/Manual Gear to be removed.  Two of the retaining screws are visible and were easily to remove, the third is difficult due to confined space for turning the allen key and the fact that the screw can't be seen making the necessary insertion of allen key at each turn very tricky and slow.

An informative video tour of the Declination Assembly on LX200 GPS (https://www.youtube.com/watch?v=3s44lmXJgRY) helped me understand how I could access the declination block.

I may investigate getting a replacement axle unit, but it is more likely that I will leave the LX200 with the Dec Knob permanently removed since I never have need to use the Dec knob manually.  Refitting the thrid retaining screw would probably be difficult with removing the Dec block.

Declination Knob after removal
Note. bend in axle (near to gear)
  Image
 
Declination Knob Axle
The bend in axle (near to gear) is more obvious in this picture
Image

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LX200 - Autostar II Settings

Working list of Autostar II settings that are used with the LX200 Scope at Clair Observatory :

Menu Set Item   Value Notes:
Setup / Align Align   Align on Home  
Setup / Date Date   From GPS  
Setup / Time Time   From GPS Blank mean 24 hour clock
Setup / Daylight Saving Daylight Saving   Yes / No Changed twice a year.
Setup / Smart Mount Configuration   Off  
         
Setup / Telescope Mount   Polar Scope is on equatorial wedge aligned to North Celestrial Pole
Setup / Telescope Model   12" LX200 12" LX200
Setup / Telescope Max Slew Speed   6 6 degrees per second (8 is fastest)
Setup / Telescope Mount Upper Limit   68 68 degrees
Setup / Telescope Mount Lower Limit -60 Approximates to southern Horizon at Dec -59d 37m
Setup / Telescope Anti-backlash   100% Number 0 to 199% to change backlash on either RA or Dec axes.
Setup / Telescope Tracking Rate   Sidereal / Custom  
Setup / Telescope Home Sensors   Off  
Setup / Telescope GPS Alignment   Start-Up GPS alignment performed at start-up.
Setup / Telescope Dec Pec   Off Not required for Polar aligned scope
Setup / Telescope RA Pec   On  
Setup / Telescope High Precision   Off Precision pointing is performed using own software (CCDApp2)
          
Setup / Targets Targets   Astronomical  
          
Setup / Owner Info. Name   D.Richards  
Setup / Owner Info. Address   Aberdeenshire, UK  
          
          
Functions Function   Used/Not Used Notes
Setup / Telescope Train Drive   - Not Used (CCDWare PEMPro used instead)
Setup / Telescope Calibrate Sensors   - Not Used
Setup / Telescope Reverse L/R   - Not Used
Setup / Telescope Reverse U/D   - Not Used
Setup / Telescope Park Position   - Not used
Setup / Telescope Calibrate Home   Used Used to stores the current telescope position as the 'Park Position'
 
Utilities Park Scope Used Used to Park Scope
Utilities Brightness Adj. as required Adjust brightness of handset display
Utilities Contrast Adj.
as required
Adjust constrast of handset display
   

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LX200 - Autostar Firmware Update to 4.2G (2016-12-20)

Autostar II Firmware was updated from 4.2g to 4.2G v19 on 2016-12-20 using a Patch kit in order to regain access to critical functions that were used with the former motherboard before it died.

 The workflow used was as follows (adapted from a workflow used in 2013)

No Step Notes
1 Reminded self of firmware status on Autostar Information Page at http://www.weasner.com/etx/autostar_info.html 
and ensured that I still had a working version of Star Patch 1.6
Determined that as of  2013-11-12 the latest Autostar II patch kit was  
"Patch Kit for v4.2g (v19) (03/31/13)"

As LX200 motherboard was a new one, there was no requirement to download & save the existing PEC table from the mount
2 Opened StarPatch 2.6 Unregistered trial version
2a Clicked on Options and selected Language (English) and Handset Type (Autostar II  (LX200 GPS)      
2b Clicked on the "File" menu and selected "Get Updates..." to download the latest files Files were downloaded ok
2c Selected required Patch File (PatchLX42ggv19.spf) and selected required options Image

I went with all the default items, together with Block Dimming, 10x finer Tracking Rate and Save Tracking Rate. See following list:

Image

2d Selected the Com port on which telescope is connected and selected Baud Rate (9600) At first I couldn't see the COM Port for the telescope in the StarPatch list of COM ports. I knew Telescope was on COM11 so clicked on "Update Autostar", assuming that StarPatch application would find the COM11, however it didn't.  It seems that StarPatch can only see active ports up to COM9 or so.   As a workaround I connected the scope serial-USB adapter lead to one of the laptop's main USB slots rather than a slot in the Observatory's USB Hub.  This then gave a COM4 port that StarPatch could finally see and use.
2e Turned off Internet Connection and checked that laptop was connected to working Power Adapter. This was based on a recommendation I read online.
(It also said something about making sure there were no cats or children around, so checked that too !)

2f Clicked on Update Autostar to update the Autostar II (LX200 GPS) StarPatch connected with Autostar II (LX200 GPS) and proceeded to update it with new firmware.   The autostar II handset gave a message like : Uploading - do not turn off handset.   Since this was going to take around 10 minutes or so, I popped back in the house. When I returned the upload status was showing 100% but there was an error message saying that Autostar had failed to update. Checking the handset indicated that it has moved to 4.2G   (from 4.2g) but none of the old settings were there.

I proceeded with a second update attempt, but this time stuck around to observe the upload.   After completing the upload, StarPatch sent a message to the AutoStar/LX200 to reset.   After resetting was done, StarPatch put the message that Update had failed  when it connect seemingly connect with the Autostar after the reset.  Whilst the message was not good, it was assumed that the Upload had probably proceeded ok.
3 Reentered Telescope and Handbox Settings Reentered various settings based on the list that was written down directly before the upgrade proceeded.  
Setting RA Pec to "On" caused the scope to begin its drive initialisation movement.
4 Connected with TheSky and Synced scope based on the scope's approximate position. Scope will need to be Synced on a actual star at star of next session.
5 Made a couple of power cycles to test
Start Up
Start Up confirmed as 'normal'.  Scope starts up at Park Position (without initialisation movement)  and proceeds to obtain a GPS fix and then wait for further instructions.

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