30 replies to this topic

[Mr Magoo]

I rescued this 1997 Celestar C8 today. It was really dirty and smelly, but I have it cleaned up pretty well. I wish our weather was better so that I could try it out. Thankfully the optics were protected and look great. 

 

The mount is not tracking in RA. I'm guessing that it may be the spur gear loose on the motor shaft. I have read about people having this exact issue over the years. I'm hoping to be able to dig into the issue in the next couple of days. 

 

It's missing the battery cover which seems to be fairly common on these mounts. Probably a hard to find piece. That might be a good candidate for someone to 3D print. 

 

t here is a 12 volt jack on the drive base which I assume could be used to power the drive with a converter. Does anyone know what Celestron offered to do that?

[RichA]

Careful what 12 volt supply you use.  Some of those junky 120vac to 12vdc have voltages that are way off.  14-16vdc true output is ok, it'll draw-down.  I would use a 12vdc 2amp switching (much lighter than the old linears) power supply. 12 volt batteries are completely safe.  My Ultima 8 would run for hours on a standard 9volt battery.

[Mr Magoo]

Careful what 12 volt supply you use.  Some of those junky 120vac to 12vdc have voltages that are way off.  14-16vdc true output is ok, it'll draw-down.  I would use a 12vdc 2amp switching (much lighter than the old linears) power supply. 12 volt batteries are completely safe.  My Ultima 8 would run for hours on a standard 9volt battery.

Thanks Rich. I need to figure out what size the male plug is that goes in the board. I wondered how long it would run on a 9 volt.

[VA3DSO]

Beautiful! My first serious scope was a Celestar 8 - mind you mine had the wedgpod tripod which was super light but not as robust as the actual wedge yours has.

 

You did a fantastic job cleaning it up! That brings back a lot of good memories.

[trip86]

Nice find! I picked up one of these a few years ago for really cheap, it had been sitting in someone's garage collecting dust for years. Despite the coatings looking a little worse for wear the views through it were great and my best planetary images so far were with it. Eventually though the awkwardness of setting it up and it being unsuitable for dso imaging meant it got out less and less so I sold it on to help fund some new scopes. I thought about deforking it but decided against it.

[Mr Magoo]

I’m trying to resolve the problem with the RA not tracking, but running into a problem. I read in another thread that the fork section can be removed exposing the motor by removing the center machine screw under the plastic plug as shown in the picture. I removed the screw, but it’s not budging. Any idea why it won’t come apart?

​

[Tenacious]

I found one of these a few years back, too.  Your tripod looks like a better design than mine came with, I've since moved it onto a Deluxe tripod and made a different wedge-plate that can be braced (starting at post #62).

 

How far are you from Rushville, IN?  There is still a well-stocked Radio Shack there on Main Street.  Bring your mount and try different barrel connectors until you find the correct fit.  On mine, the center conductor is positive.  While you're there, consider buying the components needed to make a new hand controller.   The schematics below should help you discern the wiring.

 

  

[Mr Magoo]

I found one of these a few years back, too.  Your tripod looks like a better design than mine came with, I've since moved it onto a Deluxe tripod and made a different wedge-plate that can be braced (starting at post #62).

 

How far are you from Rushville, IN?  There is still a well-stocked Radio Shack there on Main Street.  Bring your mount and try different barrel connectors until you find the correct fit.  On mine, the center conductor is positive.  While you're there, consider buying the components needed to make a new hand controller.   The schematics below should help you discern the wiring.

 

Thank you. I probably will not have a need for the hand controller. I have to get the RA sorted out before anything else.

[DAVIDG]

I’m trying to resolve the problem with the RA not tracking, but running into a problem. I read in another thread that the fork section can be removed exposing the motor by removing the center machine screw under the plastic plug as shown in the picture. I removed the screw, but it’s not budging. Any idea why it won’t come apart?

​ IMG_0465.jpeg

 You should be able to remove the top cover around the electronics to expose the  motor and circuit board. Does the LED come on and if so is it blinking or steady? The electronic were designed by Tangent Instruments. The electronics have a built in trouble shooting via the LED. If it is steady it means the electronics past it's self test. If blinking something is wrong and usually it is looking for the signal from the encoder on the motor and it didn't see it.

 

                          - Dave 

[Mr Magoo]

 You should be able to remove the top cover around the electronics to expose the  motor and circuit board. Does the LED come on and if so is it blinking or steady? The electronic were designed by Tangent Instruments. The electronics have a built in trouble shooting via the LED. If it is steady it means the electronics past it's self test. If blinking something is wrong and usually it is looking for the signal from the encoder on the motor and it didn't see it.

 

                          - Dave 

Hi Dave. I did remove the cover. I can see the motor and the spur gear, but it is not moving. I can’t tell if the shaft is turning or not. It’s hard to see because I have no reference marks to tell if it is moving. 
When I removed the screw the underside of the flat washer had a blob of some kind of sticky material. It is also on the threads and you can see it on top of the shaft. I’m not sure if it’s old grease or a thread locker. I’m thinking it’s old grease. I can see some grease on the outside of the bearing. Perhaps that’s what is keeping it from coming off the shaft.

[Mr Magoo]

 You should be able to remove the top cover around the electronics to expose the  motor and circuit board. Does the LED come on and if so is it blinking or steady? The electronic were designed by Tangent Instruments. The electronics have a built in trouble shooting via the LED. If it is steady it means the electronics past it's self test. If blinking something is wrong and usually it is looking for the signal from the encoder on the motor and it didn't see it.

 

                          - Dave 

Sorry Dave I forgot to say that the LED light is steady, but that is good to know about the self diagnostic feature.

[DAVIDG]

 On the older orange C8 the fork assembly I have worked on,  the bearing in the fork would just pull out of the shaft on the mount. Yours looks to be the same. It looks like you have a combination of rust mixed with the grease and that has the shaft stuck to the bearing. I would try a some penetrating oil on the shaft/bearing. You can hold the forks up so the base is off the surface   and then tap on  the shaft to push it out of the bearing. I bet a few light taps on the center of the shaft and  the base will drop out of the forks.

 

           - Dave 

Edited by DAVIDG, 26 May 2025 - 12:32 PM.

[Mr Magoo]

 On the older orange C8 the fork assembly I have worked on,  the bearing in the fork would just pull out of the shaft on the mount. Yours looks to be the same. It looks like you have a combination of rust mixed with the grease and that has the shaft stuck to the bearing. I would try a some penetrating on the shaft/bearing. You can hold the forks up so the base is off the surface   and then tap on  the shaft to push it out of the bearing. I bet a few light taps on the center of the shaft and   the base will drop out of the forks.

 

           - Dave 

Exactly what I was thinking of trying. Thanks Dave.

[Tenacious]

 You should be able to remove the top cover around the electronics to expose the  motor and circuit board. Does the LED come on and if so is it blinking or steady? The electronic were designed by Tangent Instruments. The electronics have a built in trouble shooting via the LED. If it is steady it means the electronics past it's self test. If blinking something is wrong and usually it is looking for the signal from the encoder on the motor and it didn't see it.

 

                          - Dave 

 

@ Mr Magoo    You didn't mention the LED - Steady?

@ DavidG  So, Mr Magoo's RA is driven by a geared DC motor and monitored by an encoder?  I've never had to get this far into one.

 

I'm now using the model with 2 9V batteries and periodic error correction.  Works great, no problem.  It came with a DEC motor as well - stepper I think. 

 

Are there docs that detail Mr Magoo's drive and my drive?  I'm curious.

[DAVIDG]

@ Mr Magoo    You didn't mention the LED - Steady?

@ DavidG  So, Mr Magoo's RA is driven by a geared DC motor and monitored by an encoder?  I've never had to get this far into one.

 

I'm now using the model with 2 9V batteries and periodic error correction.  Works great, no problem.  It came with a DEC motor as well - stepper I think. 

 

Are there docs that detail Mr Magoo's drive and my drive?  I'm curious.

 The drive I have worked on have been a DC motor with feedback to make a servo system  It uses custom programmed PIC to control the motor.  The system needs an encoder to know were in the rotation of the shaft it is so in can apply  the PEC correction to the fast and slow areas of the worm. The systems I have worked on would do a self test when it is powered on, to check to see if the motor is turning by looking  for the encoder signal. If it doesn't see it the LED would blink. 

 

                - Dave 

Edited by DAVIDG, 26 May 2025 - 12:33 PM.

[Mr Magoo]

Found this today while fiddling with the scope. One more thing to deal with. I have a variety of finders and brackets around here, but not this one. 

 

 

 

[Mr Magoo]

Well I finally got the drive apart. I wound up removing the OTA from the forks to make things easier. I still can not get the upper part with the bearing to slide off of the shaft, so I just removed the bottom bolt and got it apart that way. 
 

I removed the motor with the gear box attached and separated the two. The motor spins fine on its own. It is easily stopped with my fingers, but maybe it doesn’t have much torque and this s normal? The gear box however will not turn at all. Looks like all the gears inside are plastic. The gear that engages with the motor spins freely, but none of the others will budge. It seems like you should be able to turn the gear box by hand with the brass spur gear on the outside.

 

So what am I up against here?

[DAVIDG]

Ken,

   If I'm understanding you have powered up the electronics and the motor is running ? If so is the LED solid or blinking ? If solid then the electronics are seeing the signal from the encoder.

   As for the gear box, the gear reduction could be  100:1 and while it is reducing the speed of the motor it also increasing the torque by that amount. The result is output torque is a few inch/oz and that is then increased by driving the main gear. So just like our vintage scopes that use an AC sync motor which only have few inch/oz or torque the final torque is much increased to drive the scope.

   So it would be difficult to turn the worm to make the  gears in the gearbox to turn BUT  you should be able to turn the input gear were the motor goes and see the output worm turn.  The issue is that you may need a lot of revolutions of the input to see any movement of the output to check if it is working or not. For example if the main gear on the RA shaft has 144 teeth, the worm driving needs to turn at 1/10 RPM and since the motor maybe running at few hundred RPM there is huge gear reduction in the gearbox. So you may have to turn the input shaft a few hundred times to see any  motion on the output.

   So I would try spraying some penetrating oil like WD40 on the gears and see if things free up and you start to see other gear movement. If not it's possible that one of the gears is damaged and has missing teeth so that is what is stopping it from  showing motion all the way out to the worm.   As I said with the huge reduction also increase the torque, if the scope got stalled, a gear in the gearbox could easily have a couple of teeth broken off.

 

                   - Dave

[Mr Magoo]

Ken,

   If I'm understanding you have powered up the electronics and the motor is running ? If so is the LED solid or blinking ? If solid then the electronics are seeing the signal from the encoder.

   As for the gear box, the gear reduction could be  100:1 and while it is reducing the speed of the motor it also increasing the torque by that amount. The result is output torque is a few inch/oz and that is then increased by driving the main gear. So just like our vintage scopes that use an AC sync motor which only have few inch/oz or torque the final torque is much increased to drive the scope.

   So it would be difficult to turn the worm to make the  gears in the gearbox to turn BUT  you should be able to turn the input gear were the motor goes and see the output worm turn.  The issue is that you may need a lot of revolutions of the input to see any movement of the output to check if it is working or not. For example if the main gear on the RA shaft has 144 teeth, the worm driving needs to turn at 1/10 RPM and since the motor maybe running at few hundred RPM there is huge gear reduction in the gearbox. So you may have to turn the input shaft a few hundred times to see any  motion on the output.

   So I would try spraying some penetrating oil like WD40 on the gears and see if things free up and you start to see other gear movement. If not it's possible that one of the gears is damaged and has missing teeth so that is what is stopping it from  showing motion all the way out to the worm.   As I said with the huge reduction also increase the torque, if the scope got stalled, a gear in the gearbox could easily have a couple of teeth broken off.

 

                   - Dave

This is not the worm drive system, but rather the one with the spur gear. I’m away from home today but will try and get some pictures taken later. The spur gear coming from the reduction case will not turn even when I tried rotating it carefully with a pair of pliers. It looks like it would be very difficult to open it up.

[Mr Magoo]

This is the drive motor with the gear reduction box.

 

 

 

 

 

 

[Mr Magoo]

The black plastic gear just visible through the hole seems to be the only one that turns freely.

 

 

 

[Mr Magoo]

This is the brass spur gear that engages with large ring gear to move the mount in RA. It will not move at all. Doesn't look like it would be very easy to remove the cover to see what is going on inside without damaging it. 

 

 

 

[Mr Magoo]

The large ring gear. 

 

[DAVIDG]

 Ken,

   Does the motor run when plugged into the circuit board ? The black disk on it is the encoder and if the circuit doesn't see the encoder the motor won't run. The common failure is a  bad connection between the motor/encoder to the circuit board. The problem usually is the phone type connectors either with a bad solder joint on the circuit board especially the one on the circuit board on the motor or a bad connection in the cable connecting the two. 

   The gear box shows a 98:1 reduction so it should be difficult turn the spur gear to get any movement of the internal gears. Usually a  gear is designed so if the box is stalled a gear will break  but the result usually is the output shaft will spin freely.  This  is common on the AC Sync motor used in our more vintage scopes. So the fact that you can't turn the shaft  indicates to me that  the gear box might be OK  and also the gear the motor engages will turns freely indicates to me that nothing is jammed.

  The test would be to spin the gear that the motor engages to inside the gearbox at least 25 times to see around 1/4 of the revolution of the output shaft.

 

                     - Dave     

[Mr Magoo]

The shaft on the motor does rotate when energized and connected to the circuit board. When the motor is coupled to the gearbox the output shaft of the gearbox does not rotate. I have let it run for up to 30 minutes and the output shaft of the gearbox has not changed position.

Edited by Mr Magoo, 01 June 2025 - 01:34 PM.