Last updated: 16 May 2002
Sent: Tuesday, May 14, 2002 21:47:07 From: firstname.lastname@example.org (Bryan) Well, some background--> Being very mechanically and electronically gifted, I decided to do my own "supercharge". Everything seemed to go well except when I put it all back together it did some weird stuff. First, it was difficult to get the alignment to go successfully. Second, when it actually did say successful, everything SEEMED to work OK. I could GOTO a planet or two. But when I would sit there observing, say, Jupiter, the scope would just randomly move up. Sometimes it would move up and then pretend to be "locking on" to something, even though the autostar said it was still on Jupiter. Sometimes the motors would spin up slowly and gradually increase speed by themselves...much like accelerating in a car! After fiddling with it for a week or so, I decided to forget about it and put it in the closet. It sat there for a few months until I got my big 6" Celestron Refractor. Finding the setting circles on that big beast difficult to use, I decided to give the little ETX another shot to help me find things to point the bigger scope at. I ripped the entire thing apart, and I mean EVERY nut, bolt, and screw came off of that sucker. I cleaned and regreased everything. Then slapped it all back together again, making sure to be as precise as possible about everything. No go. My RA motor worked fine but my DEC motor now only had one speed: very fast! Even when I set the speed to 1, the DEC would move like it was still on 9! Being the type of ignorant fool I am, and never willing to accept defeat (especially from a lousy machine!) I ripped the whole thing apart again, though this time concentrating on the electronics. I broke out the handy multi-tested and had at it. I noticed the problem fairly quickly --> apparantly I had pushed or bumped the capacitor that controls the voltage applied to the motors. I noticed because one of the leads was pulled and you could see the fatter silver part that is supposed to be INSIDE the cap, not sticking out. So I desoldiered that sucked and went hunting in my "pile o' electronics junk" for a replacement capacitor. The original cap is a 220uf 25v polarized capacitor. The closest I had was a 220uf 35v and a 220uf 16v. I tried the 35v first.... I had speed control again but the motors would not move smoothly... very jerky and inconsistant. So I tried the 16v.... too slow and also jerky. NOTE: I tried the 35v again but failed to notice the polarization. BAD BAD BAD! The thing exploded! Giant smoke cloud and the foulest smell ever! It smelled like a dog had crapped right inside my ETX! Note that the polarized caps are labeled for Negative and the circuit board of the ETX (at least mine) was only labeled for Positive. Just make sure you have them opposite! I realized that it was the voltage that was important and not the farads (uf). I rummaged through my electronics salvage and came across a few big capacitors, but that were 25v. The closest 25v cap I had was a 1000uf (roughly 10 times as big physically as the 220uf). I wasn't sure about this so I asked my friend at work (he has a degree in electronics engineering, specializing in robotics) He told me it was no problem at all for this application, and the bigger cap would probably be better because its charge won't be drained as quickly as the 220uf (though i don't know how quickly the ETX motors drain it anyway) -- its fine just as long as the voltage is correct and the cap isn't too far out of tolerance. Well, I used some spare wire and soldered that to where the old capacitor used to sit on the circuit board, soldered the wires to the new (big) capacitor, and taped the capacitor out of the way to the inside of the plastic base. Careful here because the circuit board has conductive tracing on BOTH sides, and the cap is attached to that tracing on both sides! Verdict? I slapped it all back together (AGAIN! UGH!) and fired it up. All of my speed settings worked! I took the whole thing upstairs and Reset, calibrated, and Re-Trained on a water tower a few miles away. That night I took it out to give it a try. I got a successful alignment on my FIRST TRY! I was skeptical so I did a GOTO to Jupiter.... it centered right in the middle of the eyepiece. I did a GOTO to something else (I forgot, sorry) in the other direction and it also centered. Then I put it to Saturn, and it was good to. I went back to Jupiter and left it there for a couple of hours. When I came back Jupiter was still in the eyepiece, though it had drifted a little bit. I did the same thing for the next couple of days and everything went well. Before, I could only look at Jupiter (or whatever) for about 2 minutes before it would go nuts on me. This was all done in Alt/Az with high precision ON. I am going to try polar alignment some day (its not that critical to me, as I have my big scope now to do whatever I would have done with the ETX in polar mode) Sorry if this was too long, but I figure I might as well be complete just incase you had similar problems. The ETX tune up guides were extremely helpful in setting up all the mechanical aspects of this scope! If you have any questions, fire away and I'll try to answer as best as possible! -bryan
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