I’ve recently picked up another orange tube Celestron C5 Astro from an auction site, bringing my total to 3. This one is similar to the first one in terms of age, S/N 502710, but arrived in a poor state with dirty optical surfaces on the corrector, main mirror and 5×24 finder. It also arrived with a locked triangle tripod, but curiously the scope base would not mate to it – that’s a story for another day. Fortunately the damage wasn’t permanent and after it was remedied its “first light”, with me at least, revealed sharp views as I have come to expect from my other C5s.
I noticed that moving the scope in RA was not smooth, and at a couple of positions there was resistance as you rotated the tube with the RA clamp off. There was also some play in the mount such that the optical tube and forks could rock slightly. So I decided to open it up to investigate.
The base of the C5 has a central bolt which was easily loosened, actually it was quite loose already, explaining the rocking motion. Removal of the bolt allowed me to split the base into 2 halves:
You can see the RA gear wheel, and the 2 Synchro motor spur gears, which engage on opposite sides of the larger wheel.
Next I removed the gear using the 3 screws which secured it to the rest of the scope.
This allowed me to see the spur from the underside of the RA slow motion.
I was also able to remove the RA setting circle, which came with a surprise spring clip pinging off into the distance. Note to self – always take photos at each stage of jobs like this!
With the pieces lying around me I could see that there are 2 main gear wheels – one allowing movement in RA when the clamp is off, using the slow motion, and the second driven by the motors when the clamp is on. I had always wondered how this worked.
A little light clean-up and lubrication followed before reassembly of the base and attachment to the Wedgepod from my Celestar C8 (seen in alt-az position below). The rocking was fixed. Then having done a quick earthing check I ran the 220V AC motors for a couple of hours to check all was well. The reassuring sound of the motors could be heard on both sides, and the base rotated in RA as expected – very slowly!
Spinning the tuned-up scope with the RA clamp off was now much smoother and with less of a rattle. Job done.
