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LX200 EMC no power

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#1 Mike Van Buskirk

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Posted 08 October 2019 - 09:44 AM

Hi everyone.
I bought a Meade LX200 EMC Sunday for $400 and the power supply that came with it worked a couple of minutes and then quit. I am guessing the PS went out.
Used my multimeter to test the power supply that came with this telescope and I think it's bad. I dont get much of a reading on the lead that goes to the power input jack.
Sure wished I had a way to apply the proper voltage to see if this thing works. 🤔
I ordered a 16v power supply at the advice of another astronomer who has experience in electrical problems with the LX200 so I am waiting on that delivery to see if this thing works. 🤔

Edited by Mike Van Buskirk, 08 October 2019 - 01:22 PM.

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#2 Skywatchr

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Posted 10 October 2019 - 07:27 AM

Hi everyone.
I bought a Meade LX200 EMC Sunday for $400 and the power supply that came with it worked a couple of minutes and then quit. I am guessing the PS went out.
Used my multimeter to test the power supply that came with this telescope and I think it's bad. I dont get much of a reading on the lead that goes to the power input jack.
Sure wished I had a way to apply the proper voltage to see if this thing works.
I ordered a 16v power supply at the advice of another astronomer who has experience in electrical problems with the LX200 so I am waiting on that delivery to see if this thing works.

Depending on your meter, you want it set to read DC voltage above 30v, and under 200v, or whatever gets you in the range to safely read 25v DC. Make sure it is set to DC volts and not AC volts. The outer barrel of the power plug is negative, and inside is positive. Do not short them together. Hold your negative probe (black) at 90 degrees against the barrel, then take the Positive probe (red) and insert it in the center of the plug. If you read anything between 18v to 25v, the power supply is probably good. If it is the Meade 18V AC power supply, it is unregulated and will read higher than 18v DC on the output (the plug) until there is a load on it. Some of the power supplies had a built-in circuit breaker with a yellow button to reset it.

The 16v regulated power supply is *much* better, and safer than the original Meade.



#3 Mike Van Buskirk

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Posted 10 October 2019 - 09:22 AM

Thank you Skywatchr. Im not getting any reading from the PS output.

The 16v from Scopestuff.com will be here today.

I sure hope thats the problem. 


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#4 DAVIDG

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Posted 10 October 2019 - 10:34 AM

 Having repaired a number of LX200 over the years I highly recommend that you replace the 16 volt tantalum capacitors both in the hand paddle and in  base before you plug in a new supply. They need to replaced with ones rated at 25 to 35 volts.  It sounds like one of these shorted which is very common and took out your power supply. If it  is shorted it will fry your new supply. Worse,  if it is the cap in the hand paddle it can burn  the ribbon cable for the keypad   and if that happens you going to need to replace the hand paddle or replace the keypad if it is still available.  The original capacitor are rated for 16 volts and any voltage higher then that will cause them to fail. It is not if they will go bad but just a matter of when. 

   As for your power supply, you should be able to take it apart and see if there is an internal fuse. If so, the fuse might have blown and that is all it needs to get it working again,  but as I have said if the cause was a shorted cap the fuse will blow again as soon as you plug it in and may cause more extensive and expensive damage.

 

                      - Dave 


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#5 Mike Van Buskirk

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Posted 10 October 2019 - 10:43 AM

Thanks Dave. I've only soldered speaker wires in car stereo installations so soldering on a circuit board makes me worried. I do have a good soldering station though.
I opened the PS and the fuse is fine and none of the caps look damaged. Possibly it shorted internally and I can't see any physical damage?

Edited by Mike Van Buskirk, 10 October 2019 - 10:47 AM.


#6 DAVIDG

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Posted 10 October 2019 - 01:17 PM

 It could be something simple like a break in the wire of the cords to the supply or it could be one the component in the power supply like the IC that controls the switching has died. 

   There is also a fuse in the front panel of the scope that I would check. If it is bad I would be very cautious about plugging in the new supply until you find out what caused the fuse to blow. Very rarely do fuses just go bad, something causes to much current draw and that causes them to blow. The very common problem is the capacitors in these scopes. They in the hand controller, the front power panel and in the electronic in the base.  They are usually yellow in color and if bad will show signed of over heating. 

   To replacement them for those that are not  skilled at solder what I recommend is to  first mark the circuit board to show the polarity of the capacitors. The tantalum type usually has a stripe with a + marked on it to define the positive side. Then you take a pair of pliers and crush the capacitor. That will leave the two wires sticking out of the circuit board. Now you take the new capacitor and place it flat on the circuit board with the wires sticking out the side  and bend them to match up with the old wires sticking up. Try to get the new capacitor as close as possible to were the old one was and make sure that the new one doesn't interfere with closing the case or other parts.  Then take the new cap off the board  and tin the wires with some solder. Place it back on the circuit board so the wires touch the old ones sticking out of the board, being sure to get the polarity correct. Some capacitor are marked with a + and some with a - so be careful to get them orientate  the correct way.  Now just touch the  soldering iron to were each wires touch for very short amount of time like a second. The solder on the new wires will melt and  fuse to the old wires sticking up. This method keeps from over heating the circuit board and damaging the traces for those that are  new to soldering and desoldering parts.  Trim the  excess leads off.  It doesn't look as "professional" as desoldering the old parts but it reduces the chances of damaging the circuit board. 

   The capacitor in the hand paddle is the ultra critical one since the ribbon cable is right above it. If it goes, it usually burns the ribbon cable and now you need to replace the membrane switch assembly or get a complete new hand controller which are getting harder to find. 

 

    - Dave 



#7 Mike Van Buskirk

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Posted 10 October 2019 - 01:45 PM

Thank you Dave.
Yes, the fuse in the front panel is fine as well and all the yellow tantalum capacitors look normal with no signs of overheating.
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#8 Mike Van Buskirk

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Posted 10 October 2019 - 01:46 PM

Is there any specific brand and type of capacitors to replace them with?
Maybe I could get them on Amazon or something?
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#9 Mike Van Buskirk

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Posted 10 October 2019 - 01:54 PM

David, would these work?
AVX 6.8uF 35V Through Hole Tantalum Capacitor Radial, Bulk 10% (Bag of 5) https://www.amazon.c...i_M43NDb4D7KYMH
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#10 DAVIDG

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Posted 10 October 2019 - 02:35 PM

 The voltage rating  at 35 volts is fine, you just need to make sure the uf value is correct for the ones you are replacing.  I though a couple might be 10uf  but it has been awhile since I repaired one of these scopes.  There are one or two hidden capacitors in the base of the scope on the back of one of the circuit boards, so check those  has well to make sure they are OK and there might be a one in the DEC assembly as well. It just takes one of these to go bad to stop the scope from working. 

 

              - Dave 


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#11 Mike Van Buskirk

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Posted 10 October 2019 - 05:57 PM

New 16v power supply arrived and it still has no power. 🤬
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#12 Skywatchr

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Posted 10 October 2019 - 06:04 PM

New 16v power supply arrived and it still has no power.

Try it without the handbox and DEC motor plugged in.  If it still doesn't power on, remove the front power panel (4 screws) and check the fuse. It should be a 2 amp fast blow fuse. Check it for continuity with your meter because sometimes a fuse blows in the end caps while the element looks good.



#13 Skywatchr

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Posted 10 October 2019 - 06:07 PM

 Having repaired a number of LX200 over the years I highly recommend that you replace the 16 volt tantalum capacitors both in the hand paddle and in  base before you plug in a new supply. They need to replaced with ones rated at 25 to 35 volts.  It sounds like one of these shorted which is very common and took out your power supply. If it  is shorted it will fry your new supply. Worse,  if it is the cap in the hand paddle it can burn  the ribbon cable for the keypad   and if that happens you going to need to replace the hand paddle or replace the keypad if it is still available.  The original capacitor are rated for 16 volts and any voltage higher then that will cause them to fail. It is not if they will go bad but just a matter of when. 

   As for your power supply, you should be able to take it apart and see if there is an internal fuse. If so, the fuse might have blown and that is all it needs to get it working again,  but as I have said if the cause was a shorted cap the fuse will blow again as soon as you plug it in and may cause more extensive and expensive damage.

 

                      - Dave 

All the ones I have done here in the U.S. were 25v 6.8uf Tantalum capacitors. I always used at least 35v 6.8uf Kemet brand and never had a problem.



#14 Skywatchr

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Posted 10 October 2019 - 06:11 PM

David, would these work?
AVX 6.8uF 35V Through Hole Tantalum Capacitor Radial, Bulk 10% (Bag of 5) https://www.amazon.c...i_M43NDb4D7KYMH

I wouldn't trust buying anything from Amazon, or FleaBay. AVX isn't a brand name, it's the name of the Chinese peddler and there is no way to know the quality of them. But if nothing looks bad, hold off on replacing anything yet.  If need be, I can just mail you a couple of the correct ones.



#15 Mike Van Buskirk

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Posted 10 October 2019 - 06:20 PM

Try it without the handbox and DEC motor plugged in.  If it still doesn't power on, remove the front power panel (4 screws) and check the fuse. It should be a 2 amp fast blow fuse. Check it for continuity with your meter because sometimes a fuse blows in the end caps while the element looks good.

I just set my multimeter to ohms and touched the leads together.

It gave me a reading of 0.00. I tested the fuse and it said O.L.

I'd guess that's a bad fuse.


Edited by Mike Van Buskirk, 10 October 2019 - 06:21 PM.


#16 orangeusa

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Posted 10 October 2019 - 06:32 PM

I wouldn't trust buying anything from Amazon, or FleaBay. AVX isn't a brand name, it's the name of the Chinese peddler and there is no way to know the quality of them. But if nothing looks bad, hold off on replacing anything yet.  If need be, I can just mail you a couple of the correct ones.

AVX is a billion dollar manufacturer of capacitors based in the States. 


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#17 DAVIDG

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Posted 11 October 2019 - 11:00 AM

 When I have replaced the capacitors on the multiple units I have repaired  I have not used tantalum type caps but electrolytic style ones. The electrolytic units are larger but if they short they usually don't burn up and cause additional damage like the tantalum ones do. All the scopes I have repaired over the last 7 or 8 years have had no reported problems. 

  The key point thou is to use caps that are rated at least 25 volts so if there is power spike from the power supply the caps will not be damaged.

 

                 - Dave 



#18 Mike Van Buskirk

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Posted 11 October 2019 - 11:06 AM

Dave, and using a regulated 16v laptop power supply will probably eliminate all cap problems. I've been told the Meade power supply is so bad it puts out 21-22v at times. No wonder the caps burn.

#19 Spacefreak1974

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Posted 11 October 2019 - 11:32 AM

Known to blow capacitors. Our club had one and upon startup it blew two capacitors. Power supply was ok, just needed new capacitors soldered on. Also I think i've seen a recommendation to run them on 12V instead of the original recommended  voltage and they do fine and wont blow capacitors



#20 Mike Van Buskirk

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Posted 11 October 2019 - 12:28 PM

Not sure how 12v would work.
It may slew really slow.
I was told that 16v is the sweet spot between not overpowering the capacitors and slew rate that is not much slower than 18v.

Edited by Mike Van Buskirk, 11 October 2019 - 04:04 PM.

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#21 DAVIDG

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Posted 11 October 2019 - 02:09 PM

 The story goes  that Meade started out with the LX200 running at 12 volts hence the capacitors rated at 16 volts. For a 12 volt supply a 16 volt cap is OK. The scopes slewed  too slow for some users so they just upped  the voltage on the power supply to 18 volts but never changed the rating on the caps. Maybe they already had too many of the electronic made and would lose too much money having them redone ?  In any case, a 16 volt cap and 18 volt supply will result in  failure in the near future. I think they rolled the dice and hoped that a majority of failures would happen after the warranty period was up.Seems that they were right and  it is just a matter of time before the original caps fail.  Meade won't repair them and doesn't carry parts any longer  so you either fix the scope  yourself or by a third party or buy a new one.

 

               - Dave 


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#22 mdbradshaw

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Posted 11 October 2019 - 02:57 PM

I run the 7, 8 and 10 inch scopes at 12-13V.  The 12 inch will run at that speed, but any imbalance causes the motors to strain a bit with that massive OTA.  Those I run at 16-18V (always after changing all capacitors).  I also prefer running at less that MAX SPEED!!!  when slewing.  The highest slew speed (9 for the smaller scopes, 6 for the 12 inch) seems to be "throw all of the voltage you have at the motor", and they always sound strained at that speed.  Drop the slew one click and suddenly the motors smooth out, make a heck of a lot less noise, and don't have that quivering "I'm dying" sound to them.

 

As well, I have tested a 12 inch at speed 4,5 and 6.  The two slower speeds went through 90 and 180 degrees of motion in each axle in exactly the same time, which makes sense if they were under control of the board.  At top speed, the two axes traveled at different speeds (by several seconds), which means that at least one of them was not locked in by the control board, probably both. 

 

When someone says that the scope will run "slower", it means that it will take 45 seconds instead of 30 seconds to slew to the new object.  Is 15 seconds so important when you consider that you're extending the life of the scope by years?



#23 Mike Van Buskirk

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Posted 11 October 2019 - 06:01 PM

Put a new fuse in and its working!
Thanks for the help everyone. 🙂
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#24 Skywatchr

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Posted 11 October 2019 - 08:34 PM

AVX is a billion dollar manufacturer of capacitors based in the States. 

You are right. I don't know what I was thinking.  foreheadslap.gif




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