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Meade LX200GPS slewing problem

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#1 Jim Davis

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Posted 31 July 2021 - 08:53 PM

Our club has 2 Meade 14" LX200GPS permanently mounted and polar oriented on a wedge. One of our club members was using one of them last night, and it seemed to be working fine. Then it just went haywire, and started to go from east to west by turning the opposite direction, and rotating around the north side of the pier.

 

I went out today, and tried to hand set the position by turning the mount and centering it in its range of motion. Turned it on in late evening, and sent it to Venus. It went there just fine and stopped, then started back up and went another 360 back to Venus. If I sent it to something in the east, it would rotate around to the north on the way there instead of across the southern sky like it should.

 

I tried running the Calibrate Home routine, but it would get to the stop and keep trying to move until it errored with motor blocked. It should sense it is at the end, and go back and find the other limit. So right now, it's like the meridian set 180 from where it should be. So, it won't cross the meridian, but goes around the other way. Calibrate Home has always fixed that before.

 

Any idea of where to go to fix the issue? I checked all the settings, and they seem to be correct. Our other Meade 14 is still working fine.



#2 OzAndrewJ

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Posted 31 July 2021 - 09:09 PM

Gday Jim

The fact it doesnt stop when calibrating home sounds like the home sensor isnt being detected

but that shouldnt affect the normal operation for hardstop detection

The hardstop detection uses a software datum ( not the home sensors )

The datum gets set when you do an align.

If you just start up, slew to a target and synch, the mount will know where it is pointing

but has no idea of where it is relative to true "home" ( ie RA mid hardstops )

Sooooo, first thing is do a full Polar one star align. ( Just hit enter when asked to centre Polaris )

This will forcibly reset the "home" datum to mid hardstop.

After that, the hardstop detection should work properly for "gotos".

If it does, you can try a calibrate home, and if it does go into the stops

you will need to open the base and check the 2 sensors for damage or grease etc.

Andrew Johansen Melbourne Australia



#3 michael8554

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Posted 01 August 2021 - 08:17 AM

Had similar issues a while back with my LX200GPS.

 

I would routinely unpark and SYNCH on a star, but it started to get same issues as yours, fixed by Andrew's suggestion.

 

Set to Polar Home position and pretend to go through the Polar One Star alignment



#4 Jim Davis

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Posted 01 August 2021 - 05:10 PM

We took this scope apart the winter before the pandemic and cleaned it up. I didn't see a problem, and it has worked from then until now.

 

IMG_20200130_194843.jpg



#5 OzAndrewJ

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Posted 01 August 2021 - 05:36 PM

Gday Jim

OK, that piccy shows the home sensor disconnected from its normal position

so is it currently in the right place and undamaged / clean????

 

Andrew Johansen Melbourne Australia



#6 Peterson Engineering

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Posted 01 August 2021 - 05:49 PM

Andrew's spot on about clean.  If the sensor becomes covered with grease it'll do what yours is doing.



#7 Jim Davis

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Posted 01 August 2021 - 08:50 PM

Gday Jim

OK, that piccy shows the home sensor disconnected from its normal position

so is it currently in the right place and undamaged / clean????

 

Andrew Johansen Melbourne Australia

Yes, it is back in place. I do not understand how it would have gotten dirty. It has been working for over a year after we took this apart and cleaned everything.

 

IMG_20200126_165526.jpg


Edited by Jim Davis, 01 August 2021 - 08:51 PM.


#8 OzAndrewJ

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Posted 01 August 2021 - 08:58 PM

Gday Jim

I do not understand how it would have gotten dirty

Spiderweb, dust, blob of grease????

Easy test is to do the 444 test on booting.

That will tell quickly if the sensors are working

as expected

 

Andrew Johansen Melbourne Australia



#9 Jim Davis

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Posted 02 August 2021 - 07:54 AM

Gday Jim

Spiderweb, dust, blob of grease????

Easy test is to do the 444 test on booting.

That will tell quickly if the sensors are working

as expected

 

Andrew Johansen Melbourne Australia

What is the 444 test? Not familiar with it.



#10 OzAndrewJ

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Posted 02 August 2021 - 03:34 PM

Gday Jim
 

What is the 444 test?

It is an inbuilt diagnostic test.

On booting, you hit 999 to go into safeload mode.

You can also use 444 instead, and this starts up the test.

One part of the test is to check the four state changes for the sensors

If you dont get all 4, then the sensors have to be suspected.

( This test will kill any alignment if you are parked )

 

Andrew Johansen Melbourne Australia

Attached File  444Test.txt   4.97KB   17 downloads



#11 Jim Davis

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Posted 02 August 2021 - 11:09 PM

The scope passed the 444 test, I think. At least for the parts that were set up. I didn't try autoguiding or the serial ports.

 

I followed your instructions to try the polar align, it didn't help. I think the mount is really screwed up at the moment. At one point I tried to have it slew to Altair. The fork turned, but 180 away from the star. But, the OTA tried to flip completely over to go to the star, past the 90 degree position. Of course it couldn't do that. When we tried the polar align, the scope only moved up to about 75 degrees instead of 90. We tried to align on home, but it ran into a stop and restarted.

 

I think I am going to do a factory refresh of the settings, and set the scope up from scratch. The scope seems to be completely messed up. Not sure what happened, it was working fine until recently.

 

Thanks for the help.



#12 OzAndrewJ

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Posted 02 August 2021 - 11:19 PM

Gday Jim

OK, the next step is a quick encoder test.

Set the mount to AltAz mode

Set it mid hardstop in Az and with Alt = 0

Start the mount and then go to the alternate menus.

Note the reported Alt and Az  ( both should be about zero )

Slew at full speed for about 90deg in both axes

( using the setting circles as the guide to 90deg )

Once stopped, compare how far the Hbx "reports" it moved

vs the real distance based on the setting circles.

If it "reports" a lot lower value, then the encoders are suspect

 

Andrew Johansen Melbourne Australia


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#13 nitegeezer

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Posted 02 August 2021 - 11:52 PM

I have been following this thread and while I am not as knowledgeable, I have a nagging thought that the mount thinks it is an EQ with meridian flip issues. Has it been verified to be configured as an LX200?

#14 OzAndrewJ

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Posted 03 August 2021 - 12:19 AM

Gday Chuck

The current LX200GPS firmware does have some GEM specific code in it

( probably shared code for the max mount )

but there is no way in the available in the LX200 model selection options to get to it.

Something else is going on.

 

Andrew Johansen Melbourne Australia



#15 nitegeezer

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Posted 03 August 2021 - 12:35 AM

Andrew,

Thanks much for that explanation. I know there is a lot of code sharing but not sure what configurations are allowed. I thought I would mention the option as easy fixes can be overlooked!

Chuck

#16 OzAndrewJ

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Posted 03 August 2021 - 01:11 AM

Gday Chuck

No probs.

There appears to be a lot of shared code between the versions

but what can get called is based on the model selection params

for the selected firmware. It a real ratsnest, as they should have just had one

firmware for all mounts, and used the model selection to sort it out.

As it is, there are 6 to 8 different final firmwares, and each has its own quirks.

 

Andrew Johansen Melbourne



#17 Jim Davis

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Posted 04 August 2021 - 11:15 PM

Ok, I was able to fix the issue, but I still don't know what it was.

 

I went through the 444 check again that Andrew provided, and made sure that all the critical parts passed.

 

I then checked out the encoders like he suggested. They seem to be working fine. I thought there may have been an issue with the Dec encoder, and even took the arm apart to check, but found nothing out of the ordinary.

 

I then tried a few more of his suggestions, including doing the one star alignment on Polaris. After that, it went in the correct direction to Arcturus! Then slewed to Vega, and it went the right way! Did a number of park, restart, test sessions. I had to reset the custom park position, and now it seems to be working fine. Not sure which item I tried fixed it. Just in time, since a couple of our members showed up to record an asteroid occultation, and wanted to use that scope.

 

Thanks everyone for the help, particularly Andrew!


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#18 OzAndrewJ

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Posted 04 August 2021 - 11:22 PM

Gday Jim

All i can think of is at some point, you corrupted the mounts idea of its "home" datum

and this allowed the cordwrap/hardstop code to slew you the wrong way.

Anyway good to hear its working again.

 

Andrew Johansen Melbourne Australia


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