Our Meade LX200 Classic is blowing the 1.5 amp fuse on power up

[fvigil57]

My son and I powered up the telescope mount and the telescope started moving in DEC. We quickly turned it off; would not power up after that. We changed the fuse; tried again and same thing. The fuse blows almost immediately now. We are using a Radio Shack regulated power supply. Any ideas on what it is we have done this time?
Thanks and God bless.

[Skywatcher]

I am sure Dr. Clay has a better idea than I do but I will venture a guess. I have not owned a LX200 but I did work as and electronic tech for 28 years. Since you said you have a new power supply, I am wondering if the polarity of the plug is the fault. Lots of electronic equipment has  reverse polarity diode protection. Don't attempt to stop the fuse blowing by using a larger rated fuse. If it calls for a 1.5 A fuse then by all means that is what you should use.  Put an ohm meter on the non-enegerized power jack and take a reading. Also double check the power cable for correct  polarity from the supply to the scope.

Good luck.

James C
Arkansas

[drclay]

My guess is the main power board has a blown VR and/or the capacitors are out, possible in the DEC PCB driver board as well.  This is unfortunately a very common problem.
However, the place to start is the POWER SUPPLY....if you are using the one that came with the scope, throw that in the trash.  They are unregulated and many times (most times) will spike to over 35 volts and fry your electronics.  These power supplies are the number one cause of electronics failures in Meade Classic and GPS scopes....same with those supplied by Celestron.

Use only a 15 volt or 13.8 volt Radio Shack, Pyramid, or those supplied by www.scopestuff.com

These are highly regulated and work well.  Note that right now, you might test the scope using a 12 volt power supply, center pin positive always of course; the scope will run fine on 12 volts, but amperage will drop during slews or if imbalanced. 

I hope that you can find the source, but I suspect one of the factors above is the culprit.  Contact me if it continues and I will tell you how we can get the electronics rebuilt.

Doc

[fvigil57]

Thanks for the quick response. I read some of the information strings and did make the change to a regulated power supply from Radio Shack. I also took my time and made sure about the polarity.
 I suspect that what is referred to as the "Main Board" is where the slow blow fuse is located; not sure where the power board is or theDEC board. I have searched for an exploded view of the mount so as to not cause more damage unnecessarily; can someone help with that?
Also if a repair location is known that would be great too.
This telescpe belongs to a school and it is the setup they use for field trips and community outreach. The priest/moderator is along in years and I help him as much as I can; sometimes its more than I bargained for.
I appreciate the help; my experience with this is the manual and articles I can read and locations like this one. Beyond that, y learning curve is a vertical line.
Thanks again and God bless.

[drclay]

Here is the breakdown on where components are and what they do:
1) the motherboard is a large, pancake-sized circuit board that contains all of the main telescope processing and functions and commands all other boards; it is located inside the base; it is large and you cannot miss it; it typically is the cause of errant behavior when improper power is supplied or power spikes damage circuits;

2) the power board is also the front control panel circuit board and IS the one with the fuse on the classic LX200; many times you can examine that and SEE the capacitor that has burned or the main VR component. 

3) the DEC and RA driver circuit boards are located as tiny PCBs actually attached to the motor assembly itself; rarely do they go out, but if the main boards fail, typically you are advised to replace the capacitors on those along with the main board.

If you are able to remove the electronics and motors it would be far
cheaper than sending the scope down here for me to do; the problem with the
component repair with the classic LX200 is that when you change one component on one board, ALL
communications components must be upgraded on all boards.  Meade shot themselves in
the foot when they announced that these were "18 volt" systems.  Anything
but....they should be operated with 12 volts or 13.8 volts regulated, nothing more.
The best thing you can do is throw away the 18 volt power supply which is likely putting out
23+ volts.

When the electronics need to be rebuilt, I send them to Motorola where they
completely rebuild all boards, the handbox, the motors and encoders and
control boards....you are getting a state of the art upgrade with the
latest
components, not just a few replacement items.  Note that with any Classic
repair, ALL electronics must be upgraded to match the motherboard; if they
are not, the motor driver electronics will not operate properly.  Hence,
allelectronics go in for the upgrade.

The Service Fee for the rebuild is $495 plus $21 return UPS.   $516 total

On removing each piece, just make sure that you sketch a "map" of each
board placing
everything that can be removed (wires, connectors, springs, etc.) and make
sure that
you designate always which direction all the wires leave each connector
(i.e.,
"toward inside"); getting them backwards or misaligned will result in
problems of
which you are all too aware.

Yes, that does seem like a lot of money, but by comparison to other things
today, it
is a bargain. 

If you decide to have this rebuild, please send the following:

1) main motherboard
2) front control board circuit board
3) ribbon cable
4) DEC motor assembly complete (KEEP the spring)
5) RA motor assembly complete (KEEP the spring)
6) handbox
7) both coiled cords (handbox and DEC connection)



Doc

[fvigil57]

Dr. Clay,
Thanks......I will start the climb and get it done. I really appreciate the help.