Dear all,
I have a problem with my Meade ETX-125 Premium Edition.
During my observations, it often happens that ETX motors move BY THEMSELVES, AUTONOMOUSLY!
I know it's typical when batteries have low charge, but it happens when I use AC/DC alimentation!

I tried to calibrate and train motors, but the problem persists.
Actually, it's a random problem: it happens sometimes, not always, but it's a "danger" for celestial tracking!
I noticed that this trouble happens every time, switching on the Autostar, it "lose" its memory about date and time.

Do you think is it a firmware problem? (I never updated Autostar firmware)
Or what else?

Thank you very much. Clear skies!

I have an LXD75 instead of an ETX but they both use an AutoStar 497 and I had similar random slews on mine also. The first time it hapened, the battery which is a 12V lead acid battery was low. Putting the battery on the charger did not seem to solve the problem which was like yours intermittent. After much frustration I discovered that the coiled cable linking the autostar to the motor unit had and intermittent connection on one of the wires. A simple ohmmeter measurement of the cable from end to end confirmed it. I fixed the problem by making a new cable from an Ethernet Cat-5 network cable. It has essentially the same connectors but the wiring is almost completely reversed. I found the info on making the correct cable on http://members.aol.com/kewtasheck/pinouts.html. It gives info about the LX90 cables but since it is the same autostar, the info applies. No more intermittent slews now, and as a benefit the network cable was a 7 ft cable which gives me more freedom, and does not pull back the autostar like the original coiled cable kept doing. If you decide to make you own cable I would however check your existing cable to make sure Meade did not make something different on the ETX models. I confirmed that the cable I made was the same as the original cable by a simple end to end ohmeter check. If you are not comfortable with making your own cable I suppose you can buy a replacement from a Meade dealer somewhere, but I suspect it may not last, since the connectors use no strain relief to prevent the cable from pulling the wires from the connectors. I hope that solves your problem.

Claude.

Marco,

   I am glad to see that the info was usefull to you. As for the electromagnetic problem, it is most probable that the DS series is using a different motor design and it may have the problem described in this web page. Being an electronics technican I know that there can be several problems resulting in the same symptoms. I confirm you that my cable was also intermittent on the telescope side as well. As for Meade knowing about this problem, I have not contacted them myself since my scope is still under warranty and I don't want to tell I am using my own cable, in case they should decide that it voids my warranty. Since I only had my telescope for about 3 months when it hapened I assume that many people will have the problem with the cable and that Meade will hear about eventually if they don't already have.

   Make sure that the cable your friend makes has the correct wiring, using an ohmeter to check it before pluging it in the autostar since a wrong cable can damage both the autostar and the telescope.

 

Dear Claude (are you French?),
first of all, thanks again!
I'm not so expert in electronics, but I have a tester and I can measure the resistance along the wire.

My question is: the Autostar wire has 8 pins, so 8 thin "sub-wires". What's the procedure to measure resistance? Have I to remove the two connectors? If yes, what sub-wires have I to select by tester?
Excuse me for these simple questions, but I'm a novice in practice electronics, I know better the theoretical one. I bought my ETX just few months ago and I don't want to make it to burst! :-)

Thanks again.

I've just bought a RJ45 cable, but I'm seeing that its 8-pins colors are DIFFERENT from the original Autostar wire! How to solve this new problem?? Thanks.

Marco,

I am french, but from Montreal Canada not from France. I do not know what you mean by "sub-wires" but here is how to check the cable. First disconnect but ends of the cable. On each end of the cable there is an 8 pin connector. Assuming your cable is just like mine, set ohmmeter to read low value resistors since we are expecting resistance of value less than 2 ohms. Put both connector in front of you with the small wires on top. Make sure both connector are in the same orientation, that is wires comming out of cable both on the same side. With this configuration lets assume that pin 1 is on the left, that makes the pin on the right pin 8. Connect ohmeter to pin 1 on first connector and verify that you get a low resistance value when connecting other ohmeter lead to pin 8 of the other connector. Continue measuring from pin 2 to pin 7, pin 3 to pin 6, pin 4 to pin 5, pin 5 to pin 6, pin 6 to pin 5, pin 7 to pin 2 and pin 8 to pin1. Each of these connection should indicate less than 2 ohms of resistance. Note that if the test leads on your ohmeter use small wire guage you might have to substract the value read on the ohmeter when both test leads are connected together. You will probably also have to verify that there is no short in between pins, that is check that the ohmeter reads an open circuit between pin 1 and 2 of the same connector then between pin 2 and 3, 4 and 5, 5 and 6, 6 and 7 and finally between pin 7 and 8 on same connector. The wires on the connectors are very small so the tip of the test leads of the ohmeter may not be able to make contact with them, I had to use leads from a small capacitor to get inside the grove where the leads come out of the connector. If you don't have such small wires sewing needles might do the trick, but be carefull not to bend the pins on the connectors.

 I hope this is clear enough, if not let me know and I will try to include a picture.

TROUBLE SOLVED.
My friend completed the cable (a normal RJ45). The 8-wires colors are different from the original cable, but I tried the new one yesterday and it works correctly!

I think the most important "revolution" in the new cable is that it's not "twisted" (or "wrapped"?). The original Autostar wire has a lot of mass, so any slow movement causes a big inertia and so an intermittent contact on connectors.
Now, instead, I have a linear wire, without "inertial effect".

I will be sure about the new wire quality on the next backyard night, but motors didn't move during my first home test!

Thanks very much, Claude. Keep in touch. Bye.

Marco