Celestron CG-5⁴, CGEM², C6-N, C6, C8, Nexstar 8SE, 6SE, ONYX 80 EDF, Orion ST 80 A Vixen R130SF w/Porta II mount William Optics ZS110 ED APO, FLT 132 Triplet APO, SV70 ED SV115T20 Wicháhpih'a
Rural central lower Michigan
Ed Thomas Deep Space Products www.deepspaceproducts.com
Quote:The black wheel is the sensor for the periodic error correction.
You can open up the gearbox. However, this would only worth it if you can feel the motor running but the spur gear is not turning. If that is the case, then you could have a stripped gear in the gearbox.
If the problem is with the motor, then the most likely culprit is the encoder. You should take the cover off of the encoder and make sure that there is nothing in there blocking the sensor. A bad encoder is the most common problem with these motors.
You can determine if it is a mechanical problem with the mount by reaching into the housing with the motor removed and turning the worm spur gear with your finger to see if it moves.
Quote:Thanks for the info.I dont understand however the reference to the encoder. How could the encoder stop the motor from spinning? even if the encoder is broken, the motor should spin although the mount wouldnt know the position. Or I am missing something.In any case, I put the motor in the freezer, gearbox included. After half an hour or so I checked it and it doesnt work, so it seems related to temperature. I disassembled the gearbox, still not working. The only way to make it work is to nudge it manually with the arrow key pressed, then the motor suddenly starts to spin and continues until you reléase the key.It seems like the motor has "dead spots".I am considering disassembling the motor, out of curiosity, although it seems likely I will have to get a new one...
Quote:Thanks for the suggestion.I put 12V from an external power supply and it shows the same behaviour. There are some spots in which the motor does not start spinning right away but it starts if you move slightly the axis.So, I suppose the fault is not the encoder.
Quote:Sounds like it is in fact the motor. Unfortunately, the only source I know of for these motors is Celestron.Now the question is why did it go bad? It may be that the motor just went bad (these are cheap "throw-aways" after all). But you need to be sure the worm turns freely. If the axis is jammed (completely unable to move) or the worm is jammed against the ring gear, then that could result in the motor burning out.
Quote:you could use the MPJA motor but put the original gearbox and encoder on it.. "esbarton" on the CelestronCGEM forum has done something similar... I don't know how much the Celestron motor is, I know it is not available for sale outside the US..
Quote:The spur gear ("cog") that you can see inside the housing with the motor removed is attached to the worm. You can test it out to some extent by reaching into the housing and turning the spur with your finger. You can also take the cap off of the end of the worm housing and attach something like a rubber hose to the worm shaft and turn it from there.There is no way to change the gear ratios in the firmware so any replacement motor must have the exact same ratio since the encoder is located on the motor shaft rather than the gearbox shaft.