JMI motor focuser.

[paul mc c]

Hello,i have one of these for a Meade sct,it works of the key pad.....now it was working and now it is not,is there any way of checking if it is the actual motor or a fault with the key pad,the buttons on the keypad that work the focuser also are used for other tasks and they work for them.

Paul

[D4N]

Be careful, most motor focus units will use a stepper motor to allow fine control. If you apply voltage directly to a stepper motor the same way you would a normal DC motor you can destroy it.

/Dan

Sent from my iPad using Tapatalk

[cjdawson]

There is a microcontroller handbox that you can use to run the motor without the handbox. This is what I do with mine. Think is costs about £70 from telescope house. Can't remember all the details though.

[paul mc c]

Be careful, most motor focus units will use a stepper motor to allow fine control. If you apply voltage directly to a stepper motor the same way you would a normal DC motor you can destroy it.

/Dan

Sent from my iPad using Tapatalk

Thanks,The only thing i used was the Meade hand controller,surelly that would be ok.

[paul mc c]

There is a microcontroller handbox that you can use to run the motor without the handbox. This is what I do with mine. Think is costs about £70 from telescope house. Can't remember all the details though.

Thanks,How would i know if the fault is with the motor,i wouldnt want to buy the handbox and maybe still not work.

[D4N]

Thanks,The only thing i used was the Meade hand controller,surelly that would be ok.

Yes unless the hand controller is faulty it won't have damaged the motor.

What may have caused damage though is if it has worked too hard. This could happen if you use it to drive the focuser to fully in or out.

Can you turn it easily by hand when it is turned on? You shouldn't be able to if it is ok.

Damage could be in the form of broken gears, damaged bearings or burnt out coils although the latter is unusual.

It is possible to test the windings of the motor individually with an ohmmeter but you need to be able to identify which wires go to which winding. If there are 4 wires then it is bipolar and fairly simple to test, they are in pair and each pair should have the same resistance. If they are different it is likely burnt out. If there are more wires it is a bit more complicated.

A loose electrical connection or damaged gears seem the most likely cause of the problem to me.

/Dan

Sent from my iPad using Tapatalk

[paul mc c]

Strange one this,it was turning freely when it wasnt attached but when attached it only turned in both directions a small amount,it was second hand,it was a struggle to push it on the focuser,can these units be opened up.

[D4N]

I don't have a JMI one so someone else will have to answer that.

I think most things can be dismantled if you are brave enough though

Do you mean it was turning freely under power or by hand?

Have you checked your focuser locking mechanism (if you have one)? Leaving that on is a good way to break a motor focuser.

/Dan

Sent from my iPad using Tapatalk

[paul mc c]

It was turning freely under power when not fitted,do you mean the mirror lock mechinism.

[D4N]

Oh right you have an SCT.

Does it still work when not attached?

/Dan

Sent from my iPad using Tapatalk

[paul mc c]

Not now mate,there is no responce on or off the scope.

[D4N]

Hmm maybe when you pushed it on you broke something.

If it will only move a little bit under power now then it could be that you damaged the gears or the bearing when you attached it. If you are lucky a gear may have just slipped or got stuck but if they are mashed up then it could be quite difficult to fix.

The gears on my stepper are plastic, obviously this is a weak point but I don't mind. If something gets stuck I would rather have the £5 stepper motor destroy itself than it destroy the focuser!

High quality steppers will have metal gears, I don't know what JMI use for theirs though.

I'm not sure what they use to get around axial offsets either, I have a bellows coupling on mine. If the axial offset is too great then it will either not turn properly or it will break.

/Dan

Sent from my iPad using Tapatalk

[paul mc c]

The only way it moves now is if i put my finger in the housing that attaches to the focuser and move it manually,now when i do this the motor turns nice and smooth so it seems that the bearings are still nice and free,so could possibly be an electronic issue.

[D4N]

I suspect that the only option is to either give it to the manufacturer or open it up yourself and have a look.

/Dan

Sent from my iPad using Tapatalk

[Dave In Vermont]

I have 2 of these on a refractor and a 12" Meade SCT. Both work flawlessly for years - needing only an occasional 9V. battery. But I don't run them off my Autostars or Audiostars. You should be able to hear them when they are focusing - though they are quiet. Check your connections for anything that may have come loose. And drop an email to JMI - Jim will answer fast! Great guy:

http://www.jmitelescopes.com/index.htm

I'm sure you'll be up & running soon.

Dave

[MarsG76]

I have a JMI focuser and it also worked flawlessly for years.. hopefully I didn't just jinx it. It sound like your hand controller is fine if its working on other functions, but not the motor, motor seems sus.

[paul mc c]

See im not sure if it is the motor or the port on the control panel,if there was some way of checking before i either get a control hand box or open the unit up.

[paul mc c]

Actually a bit embarased about this....everything works fine...i didnt realise i had to put telescope mode on the hand set and then use the focuser mode  .

[Tinker1947]

I don't think you can turn a stepper motor by the spindle...........????  Glad you got it sorted.....