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LX200 power panel issue

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#1 SteveRosenow

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Posted 29 May 2015 - 03:03 PM

Hey all,

A couple weeks ago, I had inadvertently fried my LX200 Classic's power panel when I went to hook it up to my wife's car battery at a star party. Long story short, I mistakenly switched the positive and negative power leads to the cigarette lighter cord, which fried things up.

The first thing to blow was the 25V 2200uF capacitor on the power panel's power jack (I didn't think those things would get that loud when they failed!). I've since replaced that capacitor with an identical one I found with the same specifications on a TV motherboard, but I still cannot get the power panel to power up the telescope. A friend gave me his old LX200 Classic's electronics (power panel, main PCB and hand controller) after getting the Dudash Autostar Upgrade kit. The power panel he gave me works, but I'd like to see if it's worthwhile to fix the old one so I have a spare again.

More importantly, what could've caused the old one to fail? I've read that Meade didn't provide reverse-polarity protection and there's some writings I've seen that includes building some sort of diode bridge, but I want to know what'll fix this and what won't. I've also read that there's a diode upstream of the power jack that has a built-in fuse that can sometimes fail in an accidental hookup with reversed-polarity power cords, but I've had that diode tested and it's in working order.

I'm with very limited financial means at the moment and I'm looking for an inexpensive fix.

Any ideas?


Edited by SteveRosenow, 29 May 2015 - 03:04 PM.


#2 nitegeezer

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Posted 30 May 2015 - 12:32 AM

Electronics do not like reversed power, I would suspect multiple failures.  If you have the option of using a second set of boards permanently, you should do it.  Even if you were able to get your boards working again, they are probably a ticking time bomb.  Yes it would have been nice if Meade would have protected against reverse polarity, but before you get too upset, I would suggest you consider the cost of putting a car battery in backwards.  Just consider this a hard learned lesson.



#3 SteveRosenow

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Posted 30 May 2015 - 06:12 PM

Electronics do not like reversed power, I would suspect multiple failures.  If you have the option of using a second set of boards permanently, you should do it.  Even if you were able to get your boards working again, they are probably a ticking time bomb.  Yes it would have been nice if Meade would have protected against reverse polarity, but before you get too upset, I would suggest you consider the cost of putting a car battery in backwards.  Just consider this a hard learned lesson.

I know it's not the original main PCB in the base as that was unharmed.

Fortunately the replacement components I got didn't cost me a dime, but I have a hard time thinking it'd be every component on the board that would've failed on the power panel, as I'm able to get some voltage readings.

 



#4 adam_mizer

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Posted 31 May 2015 - 10:56 PM

Hi Steve,

Do you have the schematics to help you?

 

If not I can email them them to you.

 

John



#5 sternsplitter

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Posted 01 June 2015 - 03:14 PM

Hi Steve

 

You can also find the schematics here:

 

http://www.lx200clas...Power Panel.pdf

 

I do not have a LX200 but I see in the diagram there is some protection against reverse power (diode D1 and fuse F2). Did you check the fuse? It is intended to open if reverse power is applied.

 

Regards, Martin


Edited by sternsplitter, 01 June 2015 - 03:29 PM.


#6 DAVIDG

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Posted 01 June 2015 - 04:56 PM

 You most likely fired the 7805 voltage regulators as well.  The center tab is ground so if you check the voltage on the outer legs, one should be at 5 volts and the other in the input voltage from your power supply.

 

                   - Dave 



#7 SteveRosenow

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Posted 01 June 2015 - 05:11 PM

Hi Steve

 

You can also find the schematics here:

 

http://www.lx200clas...Power Panel.pdf

 

I do not have a LX200 but I see in the diagram there is some protection against reverse power (diode D1 and fuse F2). Did you check the fuse? It is intended to open if reverse power is applied.

 

Regards, Martin


I had Diode D1 checked at an electronics components repair/resource center three days ago and it checked out fine. 

I had actually gone there to replace the diode with a newer replacement, and asked if they could check the existing one to make sure it's in working order before I spent the money on a part I didn't need

As far as the fuse?  It checked out fine, too, at least visually. It doesn't appear opened at least as far as I can see it. 



#8 SteveRosenow

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Posted 01 June 2015 - 05:13 PM

 You most likely fired the 7805 voltage regulators as well.  The center tab is ground so if you check the voltage on the outer legs, one should be at 5 volts and the other in the input voltage from your power supply.

 

                   - Dave 

I know that all the components in the main board's PCB did not get harmed. In fact, I am using the original main PCB in the telescope right now without issue. The only thing that has fried is a component in the power panel - yet I am not sure which.

I will have a look at the sole 7805 on the power panel to see if maybe it has been fried sometime this afternoon, and will post an update as soon as that test is performed.



#9 sternsplitter

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Posted 02 June 2015 - 02:39 AM

Hi Steve

 

You did not tell us whether the power-on led is still lightening. If yes the fuse is ok, if no I am 90% sure the fuse is blown, regardless how it looks.

 

Regards, Martin



#10 SteveRosenow

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Posted 02 June 2015 - 03:21 AM

Hi Steve

 

You did not tell us whether the power-on led is still lightening. If yes the fuse is ok, if no I am 90% sure the fuse is blown, regardless how it looks.

 

Regards, Martin

 

No, the power-on LED does not light.

I will check the fuse tomorrow and report back.

 



#11 SteveRosenow

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Posted 03 June 2015 - 01:12 AM

Hi Steve

 

You did not tell us whether the power-on led is still lightening. If yes the fuse is ok, if no I am 90% sure the fuse is blown, regardless how it looks.

 

Regards, Martin

 

Martin, you were correct. And for that, I give you a million thanks!

I checked the fuse tonight. I wasn't getting current to the LED's power leads so I jumpered the fuse with a strand of 20-gauge copper wire. Sure enough, things powered up like normal! 

Thank you so much! 



#12 sternsplitter

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Posted 05 June 2015 - 09:39 AM

Hi Steve

 

I'm glad I could help you.

 

Regards, Martin



#13 sternsplitter

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Posted 07 June 2015 - 03:00 AM

Hi Steve

 

Just one remark as you did not mention it: the blown fuse must be replaced with a fuse of same type and rating.

 

Regards, Martin



#14 SteveRosenow

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Posted 08 June 2015 - 03:15 AM

Hi Steve

 

Just one remark as you did not mention it: the blown fuse must be replaced with a fuse of same type and rating.

 

Regards, Martin

Although I'm aware of that, I have it currently jumpered with a 20-gauge strand of copper wire soldered to the fuse holder ends.

It works for now, and when I have a correct fuse (once I source one) I will remove the wire.

I'm not exactly a 'newb' when it comes to electronics. ;)

I've actually refurbished the electronics in about a half dozen Meade LX5 bases, two LX6s and one LX3.




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