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Anyone ever repaired the Celestron Red Dot Finder?

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51 replies to this topic

#1 Lord Beowulf

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Posted 30 June 2016 - 12:25 AM

The topic says it all.  I know there's another RDF thread going on, but I didn't want to hijack that.  After replacing the battery again and then using a DVM to find that the original battery was still good, I've determined that some other component (potentiometer or LED) on the RDF for my 8SE is gone.  It'd be easy enough to fix if it was possible to get into the darn thing, but best I can tell that's not possible without destroying it.  Has anyone done so?  I know they aren't that expensive to replace, but frankly it's such a piece of junk in general that I could justify spending money on a new one.  If I could fix it, great, but otherwise I'll pull the mount and put something else there.

 

Thanks,

 

Beo


Edited by Lord Beowulf, 30 June 2016 - 12:26 AM.


#2 Greyhaven

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Posted 30 June 2016 - 07:24 AM

The red dot finder that came with my nexstar really didn't justify the effort of repairing it. Much better unit finders are available for little investment. Unless you're just up for a challenge and there is nothing wrong with that.

 

Grey



#3 Jim4321

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Posted 30 June 2016 - 07:36 AM

I repaired the cheesy _base_ on my 9.25 Evo several times, with no good results.  I can only think of two failures on the actual RDF unit that would be worth fixing.  One would be the lower tang on the battery contacts not making good contact.  The other would be something obstructing the tiny hole that the red dot is projected thru.  I doubt that you've overlooked those.  I think, without looking at mine, that the halves of the case are glued or ultrasonically welded, so it's hard to get at the 'guts'.

 

Good luck, and please let us know if you get into it.

 

Jim H.



#4 fitter328

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Posted 30 June 2016 - 08:05 AM

I installed the Celestron Star Pointer Pro on our 8SE's. While not the most solid piece of kit, it actually works quite well for the price and only use it for initial alignment anyways. 

 

Cheers,

John



#5 Herr Ointment

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Posted 30 June 2016 - 07:41 PM

My Amazon review.....,.here.


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#6 Lord Beowulf

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Posted 30 June 2016 - 11:52 PM

Great review Herr Ointment!   :grin:  

 

As for why bother, it's precisely because it's a piece of junk and not worth ten bucks that I want to hack it apart and take a look inside.  However, initial inspection indicates both adjustment knobs are solidly fused to the screws they drive and the seam in the body appears to be sealed as well.  Thus the question if anyone else has pulled it apart and has any guidance before I start forcing things apart and irreparably damage something that could have been salvaged had I known the trick.

 

Thanks,

 

Beo



#7 barbarosa

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Posted 01 July 2016 - 05:32 PM

Mr. o您他們太,

 

The Peoples Army wishes you to know that your identity and favorite dark site are known to them. They also call your attention to the official statement on the red dot finder.

信达一个红点取景器设计,降低制造成本的一个人民币,值得注意的是在所有工作。难以安装垫片没有,很容易把它留给电池消耗,并容易出现故障电位器或许它,目的就是不上升红星的精神观照显著。垫片,黄铜带和环氧树脂MOST解决问题。无固定电阻器的电阻黄金修复休息。

 

For  your convenience Google renders this as,

 

Cinda a red dot viewfinder design and reduce manufacturing costs one yuan, it is worth noting that the work at all. Gasket not difficult to install, it is easy to leave it to the battery consumption, and prone to failure potentiometer perhaps it is not the purpose of spiritual contemplation star rise significantly. Gaskets, epoxy MOST brass band and solve problems. No fixed resistance of the resistor gold repair rest.

 

Disassembly and repair instructions are found at the official Peoples Army Stuff site. Unfortunately the counter-revolutionary firewall precludes an English translation. The assembly drawings are classified.

 

The Customer Service Department*

 

Serving many companies around the world, language is never a barrier to good service. We always understand what we mean.


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#8 barbarosa

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Posted 01 July 2016 - 05:38 PM

Great review Herr Ointment!   :grin:

 

As for why bother, it's precisely because it's a piece of junk and not worth ten bucks that I want to hack it apart and take a look inside.  However, initial inspection indicates both adjustment knobs are solidly fused to the screws they drive and the seam in the body appears to be sealed as well.  Thus the question if anyone else has pulled it apart and has any guidance before I start forcing things apart and irreparably damage something that could have been salvaged had I known the trick.

 

Thanks,

 

Beo

Aw go ahead and just dig in, that's what I did. There is nothing to salvage* unless you are a compulsive parts saver, and there is a 12 step program for that.

 

*Feeble sarcasm


Edited by barbarosa, 01 July 2016 - 05:42 PM.


#9 windjammer

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Posted 30 October 2016 - 05:13 PM

Hi -

 

If you are still looking to do this, I fixed my starpointer today.

 

First, undo the azimuth screw (the one at the front).  Do this by placing the plastic knurled hand nut in a vice, and with a good quality philips screwdriver undo the screw - you have to break the glue or threadlocker to get it undone, which needs a bit of force, hence the vice.  The vice will damage the handnut a bit, but if careful, its not too bad.

 

Next, repeat with the elevation adjust screw, the one at the back.  The LED and front lens assembly should then just lift out.  It is attached with two wires to the lower half of the pointer.

 

Now you can fault find.  The circuit is simple: a LED, a 100 ohm resistor and and 8kohm potentiometer with on/off switch.  The issue with my pointer was the on/off switch contacts had become corroded and were not making contact in the on position.  Using a small scrwdrive I just scratched the contacts clean, and it works fine - at least for the time being.

 

Re-assembly is the reverse of dismantling.  I found that the remaining gunk on the screw threads kept the handnut tight, so the manual adjust nuts still works without undoing themselves.  If they come loose, a bit of glue would fix that I guess.

 

Hope this is useful

 

Simon


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#10 LaytonH

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Posted 30 October 2016 - 05:38 PM

Mine just broke.  You can order a new one for $13 from B&H Photo.

https://www.bhphotov...inderscope.html


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#11 lenrabinowitz

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Posted 30 October 2016 - 06:24 PM

If you can, get the starpointer pro.  Much better.



#12 Stargazer3236

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Posted 07 November 2016 - 12:03 PM

Those RDF's are so cheap, it isn't worth repairing. If you have $15-20 lying around gathering dust, just buy a new one.



#13 Lord Beowulf

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Posted 08 November 2016 - 08:56 PM

Thanks, but as previously mentioned, the RDF isn't worth replacing with a new one either.  I replaced it with my 3-D printed laser holder and never looked back.  It's been working great!  

 

Beo

 

3587.jpg link31.png


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#14 Harvest_Moon

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Posted 10 November 2016 - 06:52 AM

Get yourself a Right angled Correct image finder. Much more accurate for alignments and an investment you can move to your next scope.
The rdf was the first update I made to my scope.

Sent from my SM-G900F using Tapatalk

#15 Lord Beowulf

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Posted 11 November 2016 - 11:56 PM

You mean like this?

 

3590.jpg link31.png

 

Thanks for the suggestion, but again, off topic as far as the thread is concerned.  I wasn't asking for what to replace my RDF with, but rather if anyone had ever figured out how to disassemble one.  Windjammer actually answered the question in question.

 

Thanks,

 

Beo



#16 Bootmaker

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Posted 21 July 2018 - 04:10 AM

Thanks to Simon, AKA Windjammer, for his excellent description of pulling apart a RDPointer.

I was given a, circa 2004, Celestron 114GT Newtonian for my 50th birthday the other week, and the RDP switch failed on it’s first night out! You could see down the gap by the switch, that the wires had parted company and that the switch body was now freely rotating, as the locating pins had broken off at some point. I was thinking that separating the Alt-Az screws from the winder knobs was going to be necessary, but didn’t want to bust it with Mars opposition imminent smile.gif
Following is a photo essay of my repair to the switch. I go into a lot of detail, not because I think you’re idiots, but so that anyone, regardless of experience should be able to have success. Hope it’s helpful.

As per Windjammer’s advice, I removed the Alt and Azimuth thumb wheels, one of which I was able to do by tightly holding it with my fingers and undoing the screw with a short, stout Phillips driver. The bonds let go with a ‘click’ and the screws wound out without any damage to the plastic thumbwheels. The other thumbwheel I had to clamp (in this case in the 3-jaw chuck of my tiny model engineers lathe) in order to grip it tightly enough to break the bond. If you are able to make a matching hole in a small piece of wood, then cut it in half ( as ø ) then you can use it to clamp the wheel in a vice without damaging the plastic.
Continue winding out the screws.
The main assembly now lifts straight out of the base.

 

RDP 1.JPG

 

 

 


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#17 Bootmaker

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Posted 21 July 2018 - 04:10 AM

2. I now unscrewed the on/off switch wheel. This is a very small screw, so put it somewhere safe smile.gif

 

RDP 1b.JPG



#18 Bootmaker

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Posted 21 July 2018 - 04:12 AM

3. In parts.

 

RDP 2b.JPG



#19 Bootmaker

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Posted 21 July 2018 - 04:15 AM

4. Here is the source of my problem. The wire going from the switch to the LED broke off because the two little pins that stopped the switch from rotating had failed. Here I’ve stripped off a little of the insulation ready for soldering, revealing clean wire. An important tip with soldering: don’t try soldering the wires straight to the contact. First ‘tin’ the bare wire, that is get solder on the bare wire first. The wire can put up with fiddling around and getting the solder to melt all round the wire. If you have the soldering iron on the switch contact too long it will start to damage the switch, melting parts. By ‘tinning’ the wire beforehand (the contact on the switch probably still has a blob of useable solder on it), it means that when you place the tinned wire on the contact, and bring the soldering iron on top of it, the solder will heat up very quickly and flow together in a second or two, reducing the risk of damaging the switch.

 

RDP 2.JPG

 

(I re-attached the switch wheel for testing the circuit) Here you can see the correct circuit layout. The contact on the left also had solder on it, but when I held the wire to it the LED only had OFF/Max Brightness. The middle contact gives the full brightness control.

 

RDP 3.JPG



#20 Bootmaker

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Posted 21 July 2018 - 04:17 AM

5. Here we can see two small holes where the register pins should be.

 

RDP 4.JPG

 

These originally located with the two outer switch contacts.

 

RDP 5.JPG



#21 Bootmaker

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Posted 21 July 2018 - 04:19 AM

6. So I squirted a couple of blobs of hot melt glue over the holes and pushed the switch into place. I did a few ‘dry runs’ making sure I could place the part quickly. Make sure that you don’t get any glue on the spring, bottom right, as this controls the ‘click’ for on/off (look at the orange tab in the two photos). Hot melt glue is fairly easy to scrape/peel off, if need be. Epoxy may have worked better, but I didn’t think of that at the time.

 

RDP 13.JPG

 

RDP 14.JPG



#22 Bootmaker

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Posted 21 July 2018 - 04:20 AM

7. Initially the glue cooled with the switch at an angle...

 

RDP 6.JPG

 

…so I warmed it up with a heat gun on low, and pressed the back of the switch with a wooden handle to true it up enough. A hair drier would work. Beware: a heat gun can get hot enough to melt solder, and ruin the switch. Hold it back a bit and use just enough heat to soften the glue.

 

RDP 7.JPG



#23 Bootmaker

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Posted 21 July 2018 - 04:23 AM

8. Re-attach the ON/OFF thumbwheel. When putting screws back in threaded holes (especially if they are into plastic or wood) I like to first wind the screw backwards for a couple of turns and listen for/feel the ‘click’ as the screw drops into the original thread in the hole, then wind it in. This way I avoid making a new thread groove, or cross-threading, and stripping out the hole. I made sure that the short wire from the switch to the LED was curved back like this, below, so that, with everything back together, it wouldn’t get pinched or pulled as the RDF is adjusted up and down etc.

 

RDP 10.JPG

 

I did a quick eyeballing of the clearance with the glue, and decided that I needed to carve a bit of it off with a knife.

 

RDP 11.JPG


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#24 Bootmaker

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Posted 21 July 2018 - 04:24 AM

9. Then it was a case of gently start the winding on of the two thumbwheels with my fingers, to make sure I was not cross threading, then finishing with the screw driver. As Windjammer commented, the wheels seem to grip firmly enough without new glue, but if you find them coming loose, apply a dot of super glue to the top of the thread on the thumbwheel just before winding in the screw the last couple of turns.

 

RDP 15.JPG


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#25 Bootmaker

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Posted 21 July 2018 - 04:28 AM

10. Then wind all the way left and right…

 

RDP 17.JPG

 

 

RDP 16.JPG

 

 




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