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Telrad rewire

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#1 pyrasanth

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Posted 12 October 2019 - 04:24 PM

Sorting through my "junk" box of astro items I found a Telrad that was in a sorry state.

 

Batteries which had been left in for many years had leaked & destroyed the battery holder and the LED despite being powered directly was not working.

 

Rather than bin the unit I decided to have a look at fixing. 

 

The first hurdle was to remove the failed 5 mm LED. This is stuck into the holder with a resin compound & looks firmly glued in. Some forum information suggested drilling out the LED but I found an easier way. Remove the LED unit (which is glued into the Telrad base- but not difficult to remove) and remove the reticle which is glued in each corner. My reticle came off very easy being old- I suspect the glue had decayed. Grip the LED unit in a vice with the LED unit facing upwards and then use a medium sized posi-drive screwdriver and a rubber mallet to pop out the LED- one smart tap removed it cleanly.

 

By pulling off the power lever the nut that holds the potentiometer can be unscrewed and the entire wiring unit removed. I ordered a new battery holder and some replacement hook up wire & a new LED for for the cost of a few dollars. I've rewired everything & tested with a smaller LED that I had on hand & the unit wiring now works great. When the new LED arrives I can put it back into the holder and solder the new connections and add the reticle back to the front and re glue the holder back in place. We should then have one fixed Telrad ready to go back into service.

 

Hunting through the "junk" box I found the Telrad extension stand and a heater for the front that had never been used- So I think I have the potential to have a nice restore!


Edited by pyrasanth, 12 October 2019 - 04:25 PM.

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#2 Tempus

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Posted 13 October 2019 - 07:48 AM

If you really want a true deep red LED, you could consider this one from LED Supply. At 660nm, this little rascal is a true deep red. I've got them in two Telrads now and are noticeably more 'red' than a typical red LED.


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#3 pyrasanth

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Posted 13 October 2019 - 12:41 PM

If you really want a true deep red LED, you could consider this one from LED Supply. At 660nm, this little rascal is a true deep red. I've got them in two Telrads now and are noticeably more 'red' than a typical red LED.

Certainly this will be a good option for when I next order a few parts for other projects. I was quite surprised how primitive the Telrad build is. The battery mounting is very poor but the plus points are that the unit is very easy to tear down so can't really grumble.


Edited by pyrasanth, 13 October 2019 - 12:41 PM.


#4 Tempus

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Posted 13 October 2019 - 02:48 PM

Yeah, it's a pretty simple device. In addition to replacing the LEDs in mine, I also replaced the battery holder with a small holder for a CR2032 3v lithium battery. Probably not advisable in a really cold area, but for where I observe, I've not had any issues with it. 

 

The plus side is the battery still lasts forever and I removed the weight of the two AA batteries.  It's not a lot of weight, but that far forward on the UTA, any reduction in weight helps.


Edited by Tempus, 13 October 2019 - 02:51 PM.


#5 pyrasanth

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Posted 14 October 2019 - 01:17 PM

I've put the new LED into the holder and the unit is once again fully functional. I'm glad I've rescued the Telrad as it was, in its broken state, destined for the bin.




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