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lasjeff1
newbie
Reged: 08/30/09
Posts: 4
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Well...10 days into my new ownership of a used Meade LX90. I have a problem. Last night while observing, the scope suddenly jerked and the RA motor began running...and running...and running. In fact, the motor will not stop. Every time I turn the scope on, the scope rotate counterclockwise and will not stop. At the time I was running on a 12 volt power supply. I have attempted the following:
Reset - no help
Calibrate motors - no help
Press buttons on Autostar keypad - RA no response, Dec okay
It is interesting that the calibration seems to accelerate the scope in one axis briefly. The declination motor seems to be operating fine.
So...the following questions:
Has anyone else experienced this problem? Was it due to a motor control board fault? Is there a source for service other than Meade for board level electronics? Any way to locate parts?
As I feared, Meade has not cooperated...refused to send an RA motor control board. Their offer is send the scope, and $300.00 and we'll take a look.
Any help with repair or part resources would be greatly appreciated...thanks...
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Joe Lalumia
Post Laureate
Reged: 01/24/07
Posts: 3616
Loc: Rockwall, Texas, USA
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REVERSE the cable and see what happens. And Read This:
jrcrilly posted this on CN a while back:
"Runaways are caused by a loss of encoder feedback opening the control loop. The usual suspects are poor connections in the cabling (caused by corrosion in the connectors) or contaminants in the encoder wheel. Sometimes it's caused by corrosion within the potentiometers in the read circuitry. Exercising the connectors and/or potentiometers will usually restore normal operation if they are the problem."
First thing to try is a new cable. www.scopestuff.com sells a very nice one, more flexible and longer than the Meade cable.
http://scopestuff.com/ss_l5hc.htm
If this does not help, do a reset and reload the firmware and thy that before sending it back to Meade.
and read through this:
http://www.cloudynights.com/ubbthreads/showflat.php/Cat/1,2,3,4,5,8,9,10/Number/2082006/page/124/view/collapsed/sb/9/o/all/fpart/1
Having a problem getting the above link to work. Copy and paste the entire above link.
Edited by Joe Lalumia (09/10/09 09:59 AM)
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lasjeff1
newbie
Reged: 08/30/09
Posts: 4
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Joe-
Thank you for the suggestions...I will try them. To add a little detail, the scope rotates even when the hand control box is removed. I'm not sure if this indicates a cable failure or not...the feedback loop is certainly open somewhere but would seem to be either on the chip or the mosfet assy. Just another tidbit of information, just prior to going into the never-ending pirouette, the scope sounded like it strained a little while moving in the RA Axis. I'm not sure if a cable bound somewhere or some other issue, but my concern is the additional amperage draw may have blown a mosfet or a chip. In any event, I do appreciate the support and will try the suggestions. BTW, Do you know of any sources for board level schematics for the LX90? The AOL forum (which seemed to have some pretty good information) has closed. In any event, I will try the above suggestions and see if they improve the situation.
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Joe Lalumia
Post Laureate
Reged: 01/24/07
Posts: 3616
Loc: Rockwall, Texas, USA
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Yes-- schematics
http://jan.eaglecreekobservatory.org/powerpanel.html
http://www.weasner.com/etx/autostar/as_schematic.html hand controller
http://jan.eaglecreekobservatory.org/ LOTS of INFO on disassembly with photos
Join the LX90 Yahoo Tech Group for good advice. Here:
http://tech.groups.yahoo.com/group/lx90/
--------------------
LX90 8" LNT, SV Nighthawk & TelePOD, SV 80/9D & M4 mount, ETX 90, Orion XT10i, 20x80 binoculars, SV-BV3s-- www.texasastro.org
"Great minds discuss ideas;Average minds discuss events;Small minds discuss people." Unknown
Edited by Joe Lalumia (09/10/09 11:23 AM)
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lasjeff1
newbie
Reged: 08/30/09
Posts: 4
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I finally convinced Meade to sell me a RA drive assembly. Now I can only hope my diagnosis is correct. Thanks to all for the help.
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lasjeff1
newbie
Reged: 08/30/09
Posts: 4
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I received the drive board from Meade today and promptly replaced it. The unit now seems to work fine. Just a couple notes to the file...the mosfets are very sensitive to overamperage. Just a minor cable wrap and strain thoroughly toasted the Q2 mostfet. This could be due to the board design or the use of a 12 volt power supply that does not have amperage control. I am using a 12 volt power pack that does not have fuses or circuit breakers. Basically, when the unit asked for more power, it complied, to the significant detriment of the board. I need to check into getting a fused unit or a power pack that can't start a diesel engine on a cold winter morning. Disassembly of the unit is very straightforward and Jan's LX90 page has some excellent procedures for the disassembly, cleaning, and board replacement...very thorough. Finally, with a little begging, Meade will send out parts, they don't like to and you have to be very persistent...they really like their $300.00 repair price versus the $31.00 for a replacement board but they eventually agreed and were very cordial after we came to a meeting of the minds. I have done a lot of investigation on the electronics assembly and have some information archived if anyone has a similar issue in the future. Thanks for all the help.
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