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Celestron C5 Spotter 1974 synchron motor problem?

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#1 Gusto

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Posted 05 August 2021 - 05:59 AM

Greetings from Down-Under.

My astronomy group (we do public outreach) was recently gifted a C5 circa 1974 going by the serial number. It runs with a 12v to 110v inverter. This afternoon we plugged it in and can see that both motors are running. We removed the fork assembly from the base housing, removed one of the motors from the housing and lifted off the cap. The flywheel, if that's what it is, is spinning at a decent clip but the mount does not move at all, and it is locked. Left it running for an hour (before dismantling for a look) and there's no movement. The internals, the toothed gear and so on is pristine.

 

The scope has only been used a couple of times since it was purchased in Sydney and stored in its original case since then. The primary is in mint condition and there's a small spot of mould on the inside of the corrector plate which we'll get to. There's about six .965 eyepieces in boxes and film canisters. A T-ring for an unknown camera, counterweights and a diagonal. A couple of tubes that we have no idea what they're for, quite long actually. A D cell battery operated reticle eyepiece, the holder is corroded but nothing a bit of steel wool and contact cleaner won't fix, not that it will get used but nice to restore it to working order anyway.

 

We will mount it onto a Bunnings surveyors tripod, and will drill and tap the base of the wedge to 5/16" and repaint with some good matte black. There is some glue residue on the orange tube and we'll try and remove that with some acetone, maybe something was stuck there at some time or another.

 

So, some advice on why this little scope refuses to cooperate would be nice. Thanks for taking the time to read my first post.:-)



#2 davidmcgo

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Posted 05 August 2021 - 09:09 AM

Are both motors turning?  If just one and the other isn’t it likely would strip the gears in the good one since these were un clutched motors.

 

What are you using as reference it isn’t moving?   Don’t use the right ascension circle reading since that is also driven.  Aim it at some thing terrestrial, put in a high power eyepiece and plug it in.  If it has a slow drift it is working.

There isn’t too much to the internals.  If you loosen the motor mounting screws a bit and remove the cap at the center of the cross piece of the fork you can pull the base with motors off of the gear stack and fork.  Then put a piece of tape right on the motor pinions and see if they rotate.  Should be around one turn per hour at the pinion  but might have been different for the smaller drive base
 

Dave


Edited by davidmcgo, 05 August 2021 - 09:13 AM.

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#3 Gusto

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Posted 05 August 2021 - 03:19 PM

Hi Dave, the two motors mesh to one centre drive sprocket and both appear to be turning and this can be seen via a small hole in the upper cap. The motors have 0.75RPH stamped on the side.

We've separated the fork from the base and exposed the internals and removed one of the motors, then removed the cap from one and can see a spinning disc. The gearbox  is probably accessed from the other side of the motor but there doesn't seem to be an easy way in and as it does appear to be working that's something we're not keen on trying.

We don't understand why the mount is not rotating, or at least doesn't appear to be after running it for an hour. The RA clamp between the forks is locked and I assume that's the correct procedure to engage the drive. Maybe it needs adjusting. I will pass on the tape trick as the scope is not here right now. Cheers.



#4 jgraham

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Posted 05 August 2021 - 08:41 PM

Just for yucks point the telescope straight up, put a level across the scope, and let it run. I have had this same experience with a couple of vintage Celestrons and I swore that they weren’t tracking, but nope, they were tracking fine. I often power them using the 120Vac output from a Lithium ion battery.


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#5 Gusto

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Posted 07 August 2021 - 07:18 AM

Sorted, we put tape on a pinion and confirmed the motors are running. :-)




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