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10” LX200 Classic sparked and died

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#1 Applemaz

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Posted 24 August 2021 - 08:24 PM

Tonight I plugged my [Sceptre 120VAC 60Hz 57W to 18VDC 2A Class 2 Transformer] into the power panel on my 10” SCT Meade LX200 (Classic, no GPS) which is 18VDC and it sparked, then died.

Is this fixable?  It has been many years since I last used the telescope, but I used the same transformer years ago so I don’t know why it did this now.

 



#2 nitegeezer

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Posted 24 August 2021 - 10:59 PM

If you do a search looking for tantalum caps, you will find several threads about this.  The Classic had many failures with these caps at 18v.



#3 Daveatvt01

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Posted 25 August 2021 - 01:09 PM

The original sceptre power supplies were pretty unreliable. Also the older LX200 mounts were definitely marked 12V on the power panel, and the story goes that Meade decided to up the power supplies to 18V without changing any of the internal components, like capacitors. Between those two things and the age of the scopes, some do fail. 

Capacitors are a good place to start if you don't mind taking things apart. Likely (but not always) the bad capacitor will be pretty obvious. If you can solder, replacing the caps that take the full 12/18V is recommended and may solve your problem.

Some reading: https://www.cloudyni...ap-replacement/

 

It could be other things too. Where did you see sparks coming from? 


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#4 dcaponeii

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Posted 25 August 2021 - 01:22 PM

Ditto to above. Sparks are never good but it should be fixable.

#5 Applemaz

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Posted 26 August 2021 - 06:18 PM

I saw it spark under the panel, because it lit up there before it died.  I have basic soldering skills and own a multimeter so I should be able to pull any bad capacitors and upgrade them.  As long as the article recommends some that will fit and can handle 18v I’ll be good.



#6 Tom Masterson

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Posted 30 August 2021 - 07:54 PM

There's a fuse on the back side of the power panel. The fuse may have blown because the capacitor shorted on the power panel. If the fuse is blown, DON'T replace it and power up the mount until you check the caps. The common failure mode is to short and turn into little flame bombs. On very rare occasions they'll short and not go up in flames but it's pretty rare.

 

This place sells the caps and some other parts: https://www.clearline-tech.com/

 

I strongly suggest you check and change the 5 capacitors in your mount. Also be aware some of the older Meade power supplies were unregulated. Septre was one of them. Do a search online for 18V LX200 power supply and they are available from many places including Amazon. They are regulated laptop power supplies with the proper plug.

 

The caps are an easy fix

 

C1 on the power panel

C2 in the Handbox

C8 on the mainboard

C1 on each of the motor boards.

 

This group has lots of info in their files section: https://groups.io/g/LX200-Classic


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#7 Applemaz

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Posted 30 August 2021 - 08:45 PM

Thank you.  I ordered a lot of 10x 10 microfarad 50V capacitors to replace the 5 yellow Tantalum capacitors.  I'll be sure to check the fuse as well and look for a better power supply than the old Septre.



#8 Applemaz

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Posted 30 August 2021 - 08:51 PM

I found http://www.amazon.co...30374474&sr=8-8 on Amazon.  It's 18vDC, but I'm not sure about the tip size and polarity or amperage.  Would this one suffice?



#9 Applemaz

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Posted 05 September 2021 - 12:29 PM

LX200 Classic 25v 2200 mF Capacitor
Album: LX200 Classic
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After opening the power panel, only the 25V 2200µF Capacitor detached itself from the main board.  Nothing else seems damaged, not even the Fuse.  My CR2032 battery is also completely dead, but that's to be expected since I haven't used my LX200 Classic in over 10 years.
 
Most of the information on this site talks about the tantalum capacitors being a problem and recommends 50V 10µF replacements.  For the 25V 2200µF M4 Capacitor, should I replace with the same or something different?

Edited by Applemaz, 06 September 2021 - 08:13 AM.


#10 NearVision

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Posted 05 September 2021 - 05:43 PM

It wouldn't hurt to replace it also. Electrolytics can go bad with age. The reason for using them to replace the tantalums is that they don't blow up with a very hot ball of fire, instead they just make a mess if they blow up, which is seldom. I'd replace it with a 50V cap for the added margin. That cap is on the input and gets hit with any surges from the power supply first. And, anything near the 2200mF is good, 1800 - 2500 is close enough, it's to help filter the input power before it gets to the rest of the electronics. The only real limit is the physical size if your new cap is larger and doesn't fit.



#11 Applemaz

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Posted 05 September 2021 - 06:00 PM

Got the same rated capacitor: 25V 2200µF and put it in (though it is smaller).  In the handset I replaced the Tantalum C2 with an Electrolytic then put some Polyimide Tape over the C3 Tantalum next to it and put Polyimide Tape over the ribbon cable for added protection.

 

A couple questions:

 

1) Is it normal for the handset to get warm during operation?  

2) I have a sticker on the handset that says Revision 3.21.  Is there a newer version and can it be upgraded?

3) When I use GOTO and enter a celestial object, every so often I hear a faint noise.  I'm hoping it's the sound of the scope moving while tracking.  Does that sound right?

4) When I turn it on, the Current (mA x 100) meter fills up halfway.  Is that what it's supposed to do?


Edited by Applemaz, 06 September 2021 - 08:12 AM.


#12 NearVision

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Posted 05 September 2021 - 06:16 PM

Those old handsets make great handwarmers in cold winter. Yes, they get warm, not hot, if it's too hot you've got another problem but that's very rare.

I think that sticker is the hardware version of the handset. The CPU is in the base on these scopes and you can check the menus for which version is installed.

Yes, it makes some noise as it tracks. I'd be worried if it didn't. If you listen closely you can hear noise from the base (RA/AZ) and the arm near the OTA (Dec/Alt) as both motors move as they track.

 

Enjoy your scope!



#13 Michael Covington

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Posted 05 September 2021 - 07:19 PM

My 8" LX200 Classic had a strangely designed power inlet with a fundamental design error, a large electrolytic capacitor upstream from the fuse!   This capacitor has probably failed.   I recommend using a 12-volt power supply from now on, but before you power it up, test all capacitors, or just replace them.

More here:
http://www.covington...powerinlet.html


Edited by Michael Covington, 05 September 2021 - 07:20 PM.


#14 Applemaz

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Posted 06 September 2021 - 02:44 PM

After I replaced the 25V 2200µF capacitor on the Power Panel, I didn't know how to get at the C1 on the PCB beneath the one attached to the Power Panel.  I was afraid to just pull them apart.  After reading up on everyone recommending replacing the Tantalum capacitors, every suggestion with photos shows the PCB already taken apart.  Is there a youtube video or explanation of how to get the top Power Panel PCB separated from the bottom one?  Now that my telescope is working, the last thing I want to do is break it by pulling it apart.


Edited by Applemaz, 06 September 2021 - 07:04 PM.


#15 Michael Covington

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Posted 06 September 2021 - 07:26 PM

Glad to know the big capacitor was the culprit -- I thought it might be.  I no longer have my LX200 and am not sure how to get the boards apart.



#16 MikeBY

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Posted 10 September 2021 - 07:34 PM

After I replaced the 25V 2200µF capacitor on the Power Panel, I didn't know how to get at the C1 on the PCB beneath the one attached to the Power Panel.  I was afraid to just pull them apart.  After reading up on everyone recommending replacing the Tantalum capacitors, every suggestion with photos shows the PCB already taken apart.  Is there a youtube video or explanation of how to get the top Power Panel PCB separated from the bottom one?  Now that my telescope is working, the last thing I want to do is break it by pulling it apart.

There's not a YT that I've found but I have gone through this process. Highly recommend changing just the tantalum's that are across the 12/18v input to the 7501 5v regulator. In particular the one in the handset where if it burns it can take out a hard to replace ribbon cable with it. Basically, there's one on each circuit board. They can be tough to get to though (motor control boards). It takes good soldering skills to not destroy the double sided circuit boards.  The rest of the tantalum caps can be left alone. 
If you search here on CN you'll find posts with lots of discussion. I've posted some description myself.  The main panel circuit board comes apart there's a couple of tricks. One is the shoulder washer around the power connector. Its actually a threaded retainer holding down a wedged upper spacer. The rest is pretty easy, It can be tough to coax the modular jacks back through the faceplate. 



#17 Applemaz

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Posted 12 September 2021 - 01:45 PM

I removed the C3 Tantalum Capacitor on the Power Panel and was getting ready to replace it when I noticed the C1 nearby was fried.  Can I use the same type (10µF 50V) electrolytic capacitor I'm replacing at C3 to replace the blown C1 or does the C1 need a different capacitor?  Strangely, my LX200 was working fine even with the C1 blown (see below).

CB85B36B EBD8 4860 A6BB 440E939F4C05 1 201 A

Edited by Applemaz, 12 September 2021 - 01:49 PM.


#18 Michael Covington

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Posted 12 September 2021 - 01:52 PM

In the absence of a definitive answer, I would say yes, try it.  The capacitances on these capacitors are not very critical at all, and the voltage is certainly sufficient.

THAT capacitor may be what actually caused the problem!



#19 Applemaz

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Posted 12 September 2021 - 03:08 PM

Replaced both the C3 and C1 in the Power Panel with 10µF 50V electrolytics and it started up just fine.  Still have the C1's on each of the motor boards and the C8 on the Mainboard to do.  Not in a hurry to replace those though.


Edited by Applemaz, 12 September 2021 - 03:13 PM.

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#20 Applemaz

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Posted 12 September 2021 - 06:19 PM

I opened the base of my LX200 to look at the Mainboard (the red plastic piece that covers the amps gauge had fallen off and was knocking around inside the base) and noticed every single capacitor (C8 included) is a light blue one instead of the yellow tantalum's that are there in most photos I've seen of the Mainboard.  The blue capacitors had 25V on them.  I wonder if these were replaced at one time or if Meade used blue capacitors on the Mainboard later in their manufacturing run of the LX200 Classic.



#21 Christopher Erickson

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Posted 18 September 2021 - 02:28 AM

High priority to replace the tant caps in the Classic hand controller. If one of them blows, it often fries the proprietary and impossible-to-repair ribbon cable to the display module.

 

Clear-Line is now selling replacement (new design, newly manufactured) Classic LX200 hand controllers. But replacing the tants in the original hand controller will be a lot cheaper. LOL.

 

And those original tant caps in the hand controller WILL blow up at some point. Just no idea when.


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#22 rferrante

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Posted 21 September 2021 - 10:46 AM

They used blue and yellow at different times, but they are the same parts.



#23 Applemaz

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Posted 22 September 2021 - 07:06 AM

I did replace the Tantalum Capacitor in the handheld with an electrolytic then stuck some polyimide tape to the ribbon cable to protect it.  Polyimide (Kapton) tape can withstand temperatures as high as 230°C (446°F).


Edited by Applemaz, 22 September 2021 - 07:08 AM.

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#24 MikeBY

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Posted 24 September 2021 - 03:07 AM

I did replace the Tantalum Capacitor in the handheld with an electrolytic then stuck some polyimide tape to the ribbon cable to protect it.  Polyimide (Kapton) tape can withstand temperatures as high as 230°C (446°F).

The Kapton tape would survive but the ribbon/case would likely still melt. Kapton tape doesn't provide that much heat insulation. It's a good idea to prevent short circuits.

Be very careful with the small motor board capacitor replacement. The double-sided connections have very small, delicate traces on top that are extremely easy to damage Access is tight because of the connector pins. Some users recommended crushing the old tantalum capacitor with a small pair of pliars preserving the connection the board and then attach the new electrolytic capacitor legs to the original tantalum capacitor legs.
I've done it both ways. It's really personal preference, What is important is to verify with a DMM that you have still have connectivity from the Input voltage header pin to the input/supply pin of the 5 volt regulator. I ended up removing the RA motor/worm assembly from the base of the telescope, carefully marking the exact location of the assembly on the base plate and cap head screw locations so that it could be put back in place. It was much easier to work on this way.  Putting it back was a little tricky but the marks made it much easier. Rotate the modified board so that the access hole lines up with the grub screw used to adjust the worm spring pressure.

 

If you are running the telescope in the range of 12-15 VDC with a well regulated power supply the tantalum caps across the DC input connection will fare better, but they will always be a bit of a time bomb based solely on age.  The highest risk is when the telescope is used with the original AC power supply that is supposed to output 18VDC. Those 3rd party power supplies were not well regulated and under 'no load, low load' conditions could float up into the 20 - 23VDC range. That left no margin for the 25VDC rated Tant. caps. In contrast, Meade also supplied a step-up 12VDC to 18VDC converter to be used with a battery. It provides a well regulated 18VDC output.

I suggest replacing all the voltage input caps before running the scope, but if you do run it only use a well regulated supply no higher than 12VDC until those 5 caps are replaced. 
Also, to avoid power spikes/surges always (even after the modifications) connect and power up in this order.

1) Connect the NON-ENERGIZED PSU to the Power input on the telescope and be sure the scope is switched OFF.

2) Connect AC power source to the PSU. 

3) If there is a power switch on the PSU, Now power on the PSU and wait a few seconds.

4) Power on the Telescope.

Always turn off the Telescope 1st, then de-energize the PSU. Finally then disconnect the PSU from the Telescope.

 

Explanation: 
 

There is a large electrolytic capacitor directly across the '18vdc' power connector that helps to stabilize the power and absorb spikes.

Turning on the PSU with the scope OFF and waiting allows that capacitor to charge and the initial inrush current drops to zero.
Energizing the PSU with the telescope switched on, or worse, plugging in an energized PSU to a telescope with the power switch in the ON position creates a huge inrush current with unstable voltage and power spikes. This is how damage occurs. Some switching power supplies might shut down from the over current inrush.

More notes on the LX200 Classic design:
The LX200 classic telescope electronics have a power supply regulator on every board.to supply +5 VDC to run the electronics.

The exception to this is the motor driver circuits.  The motors run on the full supplied input voltage.  On telescopes with a "18VDC" input jack, by increasing the supply voltage to 18VDC the motors provide higher torque. The higher torque output will slew faster and improve tracking.

The handset is intentionally kept warm by the heat dissipated by the 5vdc voltage regulator. On telescopes with an '18vdc' power connector that you normally operate at 12 to 15 volts, when it's extremely cold, operating at 18vdc will help keep the handbox from getting too cold and causing operational errors.

There are several versions of main circuit board installation. Some have power resistors in the motor circuits mounted 'off the board' on brackets that use the case of the telescope to dissipated heat. Some boards use the bottom plate to dissipate heat from motor driver components. 
I found that you can improve thermal contact with the bottom cover if you remove the metal heat sink block and file the section where the device tabs connect so that the device tabs sit flush with the heat sink. You then get full contact with the bottom cover.  Be sure to clean off old and then re-apply a THIN layer of heat conductive thermal paste (typically used for CPUs) between the device tab and the heatsink block as well as on the other side of the device tab, and heatsink block where they will contact the bottom plate. Thermal paste should be as thin as possible while still achieving full contact between devices and heat dissipation. If you run at 18vdc this mod is important. 

 

Clear skies,

 

Michael.


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#25 MikeBY

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Posted 24 September 2021 - 05:27 AM

My 8" LX200 Classic had a strangely designed power inlet with a fundamental design error, a large electrolytic capacitor upstream from the fuse!   This capacitor has probably failed.   I recommend using a 12-volt power supply from now on, but before you power it up, test all capacitors, or just replace them.

More here:
http://www.covington...powerinlet.html

Hi Michael,
I must strongly disagree with your assessment and recommended changes both to the circuit and the fuse values.

These are NOT  design errors.

The purpose of that 2200 uf capacitor is to stabilize the input voltage during load fluctuations caused both by initially turning on the telescope and also when motors activate to slew the telescope. Your modification defeats the first part of that functionality and also causes MORE problems when power is switched on.

Meade designed and anticipated that the telescope would be used with a wide variety of power sources, wiring and conditions. Everything from "D" cells in the fork arms to .L-A car batteries with DC-DC step-up voltage converters and AC to DC power supplies using both short and long cables.
Meade also anticipated that the wiring may be lengthy, and in fact supplied long (25 foot) fused DC power cables for use with the telescope. Power supplied with these cables will experience voltage fluctuations directly proportional to load changes due to the resistance of the cable and change in current. 

The proper sequence of applying power is

1) connect all power cables.

2) With the Telescope OFF, energize the power supply or connect the DC power source.
3) Turn on Telescope.

The 2200uF capacitor charges when the power supply or DC power source is first energized BEFORE the telescope is turned on.
When the Telescope is turned on there is a large power demand and inrush current. The 2200uf capacitor supplies power to equalize and level the voltage as the inrush current causes a power source voltage drops due to the resistance of the long supply wires. It also reduces the apparent load on the power supply which can prevent an over-current shutdown or power supply failure from excessive inrush current. 

Your modification causes INCREASED inrush current when the telescope is turned on. The power source must simultaneously supply current to power the telescope electronics AND charge the 2200uf capacitor.  The high inrush current can result in a significant voltage drop and increases the risk of power supply overcurrent protection shutting off the power supply. During this time the 2200 uf capacitor is charging so no protection from voltage glitches or spikes is provided. 

With poorly regulated power supplies not only does the power glitch downward, but the voltage recovery at the end of the inrush period may cause a positive overvoltage spike. 

When the power is disconnected the capacitor is left in a charged state that can cause an accidental high current discharge. 

 

Regarding the fusing change to a "compromised" fuse value:
This should tell you right away that there is a problem with your modifications.

The input fuse protects the LOAD  (telescope electronics) from an event that causes excessive power use. Increasing the design 1A slow-blow fuse to 1.5A is a 225% increase in power. (18 watts vs 40.5 watts @18VDC). There is NO justification for this loss of protection. 
When the fuse is at the output connector of a power source it is protecting the source and should be sized based on the capacity of the power source. When a wire is fused, the fuse should be located at the INPUT connector of the wire and is sized to protect THE WIRE from current in excess of the wire rating. When a load device is fused, it is on it's input and is sized to protect THE LOAD from faults causing excessive power draw. The 2500 uf capacitor is ahead of the load in the design, so isn't protected by the load(internal) fuse. It is connected directly to the wire. The WIRE fuse protects the wire from excessive current should the capacitor fail in a 'short' mode. (40 watts).

The correct use of the Meade supplied power accessories

1)12VDC battery - Use Fused Mead cable. (Fused cigarette plug to barrel connector) connected to the INPUT of the

DC-DC 12-18v step up converter. 18vdc output connected to Telescope

2) AC powered 18VDC power supply - connect output of power supply to telescope. If using an extension cable, the fused end should be the female connector that attaches to the power supply.

 

Regarding the Grounding of the telescope and your modification of the circuit feeding the ammeter

The purpose of measuring current draw on the GROUND (negative) side of the circuit is to identify ground loop currents caused by multiple Earth connections.

If the power source is located 25 feet away and it is tied to EARTH, and the Telescope is tied to EARTH through the tripod, the ground loop current will generate voltage drop across the 0.1 ohm resistor and will show up on the ammeter.

This is important and significant. By bypassing the resistor you have disabled a safety indicator. 

When a ground loop exists, there can be a significant shock hazard.

 

With any DC powered device, there is often some debate about if the power return (negative power lead) should be grounded and if so how and where. 
There are several considerations

1) Safety
2) Ground loops
3) Ground currents.

 

Internally, each of the classic LX200's circuit board ground planes are tied to the mount's chassis and fork arms and each other via internal wiring. The mount is grounded via the tripod to EARTH.
Of course, if you isolate the tripod legs from EARTH, you end up with a telescope that is "NOT GROUNDED" 

The second question is that of the Power Supply.  Batteries in a battery box or Automotive power is NOT grounded. The single EARTH ground point is the Telescope Tripod. 
AC  - DC power supplies may or may not be tied to Earth Ground or may have an option to tie the negative output to ground. 

Typically, they are NOT grounded, again leaving the Telescope Tripod as the single EARTH point. 

What you want to avoid is electrical systems with more than one connection to EARTH separated by some significant distance. This can create a "ground loop" that causes noise and can present SIGNIFICANT SHOCK RISK based not on the voltage of the electronics, but on the potential differential between the two EARTH points that can cause high Ground Currents.
The purpose of measuring current draw on the GROUND (negative) side of the circuit is to identify ground loop currents caused by multiple Earth connections.

If the power source is located 25 feet away and it is tied to EARTH, and the Telescope is tied to EARTH through the tripod, the ground loop current will generate voltage drop across the 0.1 ohm resistor and will show up on the ammeter. 

The Telescope should be at Local EARTH potential as the USER touching the telescope will also be at the the same Earth potential and will not have a shock risk. Only in very unusual circumstances should the Telescope ever be "isolated" from the local Earth ground plane.
 

Thanks for your consideration regarding your self-published modifications.

 

 

Michael.




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