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Celestron Ultima C8 drive issue

SCT Celestron
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#1 PNWjohn

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Posted 27 January 2025 - 07:10 PM

My Ultima 8 was purchased from Orion Telescopes in 1989.

 

It has not been used for the last 10 years but has been stored well and never out in the elements.

 

I replaced the batteries and I it appears to charge based on the LED lights.

 

The drive is not working though. The worm gear turns freely so the mechanism is not locked up,

 

I have isolated the issue to the circuit board as there is no voltage feeding the motor. According to Celestron I should see 12 VDC from the leads.

 

Does anyone have any experience with this?  IMG_1447.jpeg IMG_1445 2.jpeg



#2 PNWjohn

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Posted 28 January 2025 - 12:47 PM

I found a post from the past on this and some great history.

https://www.cloudyni...s-my-c-11-made/

 

The circuit board shows a number TKO4/88

I am trying to find a schematic or perhaps a working board.

 

Thanks

 

 

Attached Thumbnails

  • TKO4:88.jpg


#3 CharLakeAstro

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Posted 28 January 2025 - 07:55 PM

You might consider migrating the motor and control board to the newer 9V. Motor speed is the same (359 tooth worm wheel)

If you have interest in this, let me know.



#4 DAVIDG

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Posted 01 February 2025 - 12:27 PM

 I have worked many telescope electronics. If the motor is 12 volt DC then the electronics most likely work to make Pulse Width Modulation signal. So I would  work backwards from the motor looking for were the signal stops. There is most likely a transistor that is used to take the low current pulses from the circuit that produces the correct frequency and pulse the high current 12 volts that powers the motor. So that is first place I would look to see if the signal is getting to that transistor(s).

   I would also look for a bad solder joint since the electronics of been setting for a long time.  If you post a close up picture of the board  so one can easily read the part numbers I most likely can give you a good idea of how the circuit works and were to start to look for a problem.  

 

               - Dave 



#5 DAVIDG

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Posted 01 February 2025 - 12:46 PM

 I just saw a picture the circuit board in the thread you that you listed.  I would double check that the motor is 12 volts DC and not 120 volts AC since the circuit looks to making a AC wave form. There are two transistors with heat sinks and that indicates to me  that circuit maybe making 120 volts AC and varying the frequency.  My guess is that circuit is similar to modern day 12 DC to 120 AC inverters that do not use large transformers that the old designs did. If so what the circuit maybe doing is taking 12 volts DC and pulsing it at high frequency  into  a small transformed to step it up 120 volts AC and then rectifying it to make 120 volts DC. Then circuit pulses the 120 DC to the motor to make a 120 AC that one can  select the  frequencies around 60 hz to drive the motor. 

 Are you running the scope with the hand controller plugged in because some circuits won't run without the hand controller plugged in. Also have you  checked that the battery is charged up to 12 volts  since the circuit looks to run off the battery.  Have you tried the scope with external 12 volt supply plugged in ? 

 

              - Dave 




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