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classic lx200 electronic issue, need advice.

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#1 Gombies64

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Posted 10 August 2020 - 10:07 PM

confused1.gif   Looking for advice on locating source(s) of electronic issue after startup of seldom used 1998 Meade lx200.   Scope seldom used and I haven't turned it on over a year. Seldom used every year for about 19 years do to long working hours at job. Going to be 65 yrs old now and I just retired looking forward on lots of observing. I joined this group way to late as this is 1st issue I ever had with my scope. I was unaware of Meades power supply and cap issues !

     Heres what happened. Hooked up power supply (the scepter 18 volt) ,H/C, and dec cable. Turned on power supply and then  the "on"

switch on power panel. No lights, any thing, no sounds.  The 1.5 amp slow blow inline fuse on the power supply blew. Try #2. I just replaced the fuse with the same exact one and figured why not.  Same thing. Nothing. no lights even blinked on, no sound no smell. Try # 3.  I happened to have another power cable for the power supply that felt the 1.5 amp fuse. Seemed like a dead short so I put in my last same fuse size/type and ....same. I was done. 

     Just out of curiosity I check the voltage on power supply and was at 22 volts !!!

Ok.. This is when I went looking for MAPUG which is great for anything Meade +. I finally found this site and never had a clue about the power supplies and caps.

     Next-I purchased a 12 volt, 6 amp computer supply, some 6.8uf-50 volt electrolytic caps, and a cr2032 battery, a temp regulated soldering iron and more 1.5  and 2 amp slow blow fuses. I knew I had to at least attempt to change the power panel and hand controller caps. I pulled the power panel out and nothing looked or smelled fried. The 2 amp internal fuse tested good. 

    - I replaced the c1 cap in the front power panel and then the C2 in the hand controller. 

    - I hooked up the new 12 volt power supply (with my 1.5 amp inline fuse and turned the power supply on and then the front panel switch 

       on. The power on indicator light came on and 2 bars on the ammeter lit up.

    -(Note, I always powered off before hooking up anything else to the power panel)

    -Next I tried the hand controller cord only in the panel .(same lights on.) OK. I removed the cord then.

     - Then the dec cord only. (same lights on ) OK. I removed cord.

     - I plugged hand controller cord with hand controller attached. Turned power on. Same lights came on power panel and on the hand 

       "Meade" lit up along with the rest of the hand controller lights. It stayed on "Meade", no further.

    - Installed the power panel back in the scope and reattached main board ribbon cable.

    -I hooked up nothing to the power panel. I turned it "on". All the lights on the ammeter came on and where flashing on and off steady   

      about every second, they were much dimmer now. the power on light was also dimmer. The inline fuse then blew after about 15  seconds.    

     - I powered down and removed the front power panel again. The 2 amp fuse tested ok.   I unhooked the ribbon cable again and plugged in only the hand controller.   I powered it on again and the ammeter was back to two bright bars and the power on light back on.

    - Also, should I ditch that 1.5 amp slow blow fuse ?

       - So now I am wondering where I go from here.

         - I am not an expert electronic guy by no means and do the best I can with it. 

          I would appreciate any do it yourself advice to at least locate the cause of this problem and go from there . 

             Thanks to anyone who can help out and appreciate anyones advice. 

         

 

 



#2 John Rogers

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Posted 10 August 2020 - 11:31 PM

I recently rebuilt an LX200 that was blowing fuses.  It turns out that the capacitor on the Dec motor control board was blown.  I replaced the dec control motor board and everything was back to normal.  Have you tried disconnecting the DEC cable and powering up?  If it is the DEC board, then the RA motor will work normally.

 

If you were measuring the the 22V without a load on the transformer, then that would not be unusual.  The spec voltage of 18V is under normal load.


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#3 Gombies64

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Posted 12 August 2020 - 08:52 AM

Thank for your reply. The Dec motor and cable were not hooked up after I replaced just the two capacitors and turned the scope power switch "on".. All I had hooked up to the front power panel was the ribbon cable to the main board. Your suggestions / comments / questions  are really appreciated !



#4 John Rogers

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Posted 12 August 2020 - 08:59 AM

Check out this site: https://clearline-te...roducts.html.  

 

I replaced my front panel with the one with the boot emulator and it works great.  The boot emulator will allow one to control the telescope via computer, without plugging in the handset.


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#5 rferrante

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Posted 12 August 2020 - 01:18 PM

Try checking/replacing the tantalum cap on the RA board, and the one on the main CPU board (C8).

--Rob


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#6 Gombies64

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Posted 14 August 2020 - 08:02 PM

Try checking/replacing the tantalum cap on the RA board, and the one on the main CPU board (C8).

--Rob

This will be my next step(s).  Was hoping I would luck out with the other 2 caps but this must be done either way. Moving forward, Thank you for advice !



#7 Michael Covington

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Posted 14 August 2020 - 09:34 PM

I always ran my 8" LX200 on 12 volts.  In any case, I agree with others that you probably have a shorted capacitor.


Edited by Michael Covington, 14 August 2020 - 09:35 PM.



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