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LX200 Classic: runaway Dec and then dead

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#1 LoveChina61

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Posted 16 April 2021 - 02:03 PM

I just turned on my LX200 "8 Classic (EMC) after not using it in more than 6 years. The Dec motor began running away. I saw the word "Meade" display on the handbox but not sure if it ever made it past that. I turned it off and tried it again with the Dec knob loose this time and it spun around freely. I shut it down and then started it up for a third time. This time the power light came on for a few seconds and then nothing. Dead.

 

I have disconnected and then reconnected the Dec cable and the handbox cable. I changed to another power supplier that is brand new (16volt, regulated). I took off the front panel and changed the CR-2302 battery there. The fuse behind the front panel was not burnt out, I did not see any capacitors burnt out (I had already replaced the old-style capacitor), and I did not smell any burning of electronic circuitry during the whole process.

 

Please let me know if  you have any advice. I am in London so also please let me know if you know anybody in the UK who can repair these Classics in case I am not able to do so myself.

 

Thanks for any help that you can provide!

 

Mike


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#2 Jim Waters

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Posted 16 April 2021 - 02:26 PM

FYI

 

Meade Advanced Products Group - http://skymtn.com/ma...onomy/index.htm

Groups.IO Meade - https://groups.io/g/LX200-Classic


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#3 Supernova74

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Posted 16 April 2021 - 03:14 PM

Um!? Differcult one sounds bit like a dodgy encoder fault,also woundering if there was a thought with Dec axis motor,I’m woundering if it would be worth if you could borrow a handset or something try that way.


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#4 LoveChina61

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Posted 16 April 2021 - 03:18 PM

Due to the virus, the local astro club has not been meeting face to face ever since I arrived recently arrived here. I will try to see if I can borrow a handset eventually. Any other possibilities that I can check on in the meantime?

 

Update: I just took apart the handbox and did not find anything wrong. I had previously replaced the capacitor inside the handboxl and it was still in very good condition.

 

Mike



#5 Skywatchr

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Posted 16 April 2021 - 04:42 PM

I just turned on my LX200 "8 Classic (EMC) after not using it in more than 6 years. The Dec motor began running away. I saw the word "Meade" display on the handbox but not sure if it ever made it past that. I turned it off and tried it again with the Dec knob loose this time and it spun around freely. I shut it down and then started it up for a third time. This time the power light came on for a few seconds and then nothing. Dead.

 

I have disconnected and then reconnected the Dec cable and the handbox cable. I changed to another power supplier that is brand new (16volt, regulated). I took off the front panel and changed the CR-2302 battery there. The fuse behind the front panel was not burnt out, I did not see any capacitors burnt out (I had already replaced the old-style capacitor), and I did not smell any burning of electronic circuitry during the whole process.

 

Please let me know if  you have any advice. I am in London so also please let me know if you know anybody in the UK who can repair these Classics in case I am not able to do so myself.

 

Thanks for any help that you can provide!

 

Mike

Take the DEC cover off to see if any critters decided to make a home in there. While you are at it, wiggle and jiggle the plugs on the board, and on the inside of the fork where the DEC cable plugs into. It's just a coupler so the contacts can be oxidized.  You can power it up w/o the handbox, but it won't boot or anything. But will let you know if it will power up again.  Then after that, remove the bottom cover to have a look there too.  Same thing, wiggle and jiggle the wires and cables.


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#6 LoveChina61

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Posted 16 April 2021 - 05:57 PM

Thanks. I will give that a try tomorrow.

 

Mike


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#7 LoveChina61

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Posted 18 April 2021 - 04:10 PM

I have yet to pull the DEC covers off, but today I tested both power suppliers with a multimeter and they are both working correctly. I also took off the scope's bottom plate to have a look at C8 capacitor and it was in perfect condition.

 

Am I correct in assuming that my two problems (DEC runaway, and scope does not show it is receiving power) are two separate and unrelated problems? 

 

I would like to see if I can get the front panel lights to come on when I plug in the power supplier and turn the scope on (without the handbox plugged in). Any other suggestions on why the scope is not getting any power to it at all now? I don't think a bad "pot" would keep the scope's power from coming on, but what about one of the other C1 capacitors that are mounted on each motor controller (x2)? Would a bad chip on the motherboard keep it from showing any power whatsoever?

 

Thanks,

 

Mike


Edited by LoveChina61, 18 April 2021 - 04:11 PM.


#8 Daveatvt01

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Posted 19 April 2021 - 11:51 AM

Hopefully the already-mentioned fixes of cleaning contacts, checking inside the dec cover, and booting without the hand controller will give you some clues as to what is going on. If it doesn’t, and I was in your situation, I would:

1. Replace all tantalum caps that receive full voltage, if you haven’t already done so (c2 in hand controller, c8 on main board, c1 for ra, c1 for dec).

2. Replace the slow blow 1 amp fuse.

Often when caps and fuses go they have obvious signs they are bad, but not always.

One common runaway fix is cleaning electrical contacts (which happened to me once), and a bad cap can cause the fuse to blow resulting in no power. That would be best-case scenario... it could be a lot of other things too. I don’t have experience going through electronics trying to find where power disappears so that is where I would start. 


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#9 LoveChina61

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Posted 19 April 2021 - 03:59 PM

Take the DEC cover off to see if any critters decided to make a home in there. While you are at it, wiggle and jiggle the plugs on the board, and on the inside of the fork where the DEC cable plugs into. It's just a coupler so the contacts can be oxidized.  You can power it up w/o the handbox, but it won't boot or anything. But will let you know if it will power up again.  Then after that, remove the bottom cover to have a look there too.  Same thing, wiggle and jiggle the wires and cables.

I was able to open up the DEC cover and have a look inside. Very clean. Jiggled all of the wires and found that the wires connected to the two light diodes was loose. This could have definitely been the cause of the DEC runaway since these lights help the scope determine its current location.

  Not sure why the scope is not receiving any power, however. I heard it make a faint whistling sound when I plugged in the power supplier and turned the scope on today but the sound quickly faded away while the front panel power lights remained off the whole time. I could not replicate the whistling sound through repeated attempts but my wife agrees that she heard the faint sound for a very brief moment as well. 

  Also tested the large blue capacitor on the backside of the front control panel. It connects directly to the power supplier input socket. The capacitor is still working well.

  Have checked all five of the "troublesome capacitors" that the LX200 is noted on having. Front panel, handbox, motherboard, and the capacitors on the DEC and RA motors all looked to be in great shape although I did not test them with a multimeter.

  I think I can fix the DEC runaway by firmly attaching the two light diodes and adjusting the "pots" as I have read of other doing. But still not getting any power to the scope at all.

  If you have any more advice, I would appreciate it.

 

Mike


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#10 rferrante

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Posted 20 April 2021 - 01:38 PM

As mentioned, even if the capacitors look OK visually, they could still be shorted. If you have a way to test continuity across all 5 of them you should.

 

--Rob



#11 LoveChina61

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Posted 23 April 2021 - 04:22 AM

I was finally able to fix the scope after all of your input and the input from some additional friends as well. It turned out that I needed to replace the C1 capacitor on the RA board even though it visually appeared to be in pristine condition.

 

I used some glue to anchor the photon wires back onto the side of the DEC motor from where they had wiggled free and that solved the DEC runaway problem.

 

Thanks again. I really appreciate everyone's willingness to help out!

 

Mike


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#12 michael8554

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Posted 23 April 2021 - 11:44 AM

I'm in awe of your patience and perseverance.......

 

Michael


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#13 Skywatchr

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Posted 27 April 2021 - 09:15 AM

I was finally able to fix the scope after all of your input and the input from some additional friends as well. It turned out that I needed to replace the C1 capacitor on the RA board even though it visually appeared to be in pristine condition.

 

I used some glue to anchor the photon wires back onto the side of the DEC motor from where they had wiggled free and that solved the DEC runaway problem.

 

Thanks again. I really appreciate everyone's willingness to help out!

 

Mike

Awesome!!!!  Now, if the Tantalum caps haven't been replaced, do so before they pop and cause irreparable damage. Especially in the handbox that blows a hole in the ribbon cable.  The ones in question, and in "dangerous" spots in the power circuits are a 6.8uf/25v and should be replaced with 6.8uf/35v, or preferably 50v modern Tantalum. Tantalum caps explode with a vengeance complete with flames and smoke signals. Make sure the polarity is correct when installing them too. Always double the voltage for Tantalum caps. 18v x2 is 36v so 35v minimum. 25v was "ok" for the 12v early LX200 and Meade never updated them in the 18v models.




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