Last updated: 30 June 2002
Sent: Saturday, June 29, 2002 5:46:37 From: firstname.lastname@example.org (Bruce Dickson) Great site! I'm trying to improve the dec axis locking of my ETX 105 - it looks like I need to remove the optical tube from the forks to get to the clutch. Has anyone (besides Clay :) ) experience with this? (I tried searching the archives for any ideas, but the '105 seems to be quite different to the '90 and '125 models.) TIA BruceAnd:
I decided to take the plunge, and dismantled my '105. As suspected, it's quite a bit different from the other models - the primary difference being that it is _not_ possible to remove the tube by slipping it out of the mount with 1/4" Whitworth bracket attached. This makes using the '105 as a guide scope a more difficult than the other ETX models. I found that the declination axis lock is _much_ more positive now that the clutch is free of grease. Here's the drill I used for a complete strip down. Photo's to follow once I've downloaded them from the camera, but for now this might help someone who's trying to degrease the clutch or mount it on a larger instrument. LHS refers to the left hand side when the tube is viewed from the eyepiece end. Clear, dark skies Bruce ---------------- 1. Make sure the lens cap is on. Remove the batteries, controller, finder + bracket and focus knob or electric focusser (if fitted). 2. Remove the 3 screws in the rear plastic molding on the same surface as the focus knob. (I've called this the EHA - for eyepiece holder assembly.) These secure the tube into the mount. The optical tube can now be gently slid out. Note that the flip mirror will be exposed inside the EHA, so you could clean it if necessary. Set the optical tube aside, so that it won't roll off your bench ;-) 3. Remove the locking nuts and declination scales from both fork arms. Remove the brass ring from the RHS shaft. Remove the 3 screws from the LHS and RHS plastic covers on the fork arms. Remove the outer plastic covers. Removal of the inner plastic covers can only be done after steps 6 and 8 below. 4. Turn the scope over, and remove the 3 rubber feet from the base. There are screws under each of these that secure the cover to the RA drive mechanism. Remove these screws, and carefully lift the cover. The battery box has two wires which are fairly short, and care is needed to prevent them being damaged. 5. Inspect the edge of the aluminium casting. There is a notch cut into it. Rotating the base will allow the notch to be alligned with the screws that secure the fork arms. Loosen the screws than hold the LHS fork arm, then remove them one by one. I found it was necessary to use a little "Prestik" on the end of my Allen key, to prevent the screws falling into the base. (Prestik is a locally manufactured grey goo, that's often used to stick posters onto walls - I don't know of a US equivalent, but there are several in ZA.) 6. The LHS fork arm is now loose, and can be eased out of the base. Take care not to damage the plastic pin that the scope rotates around, as you remove it from the bearing. You can leave the 3 screws that secure the bearing in the LHS fork arm in place. 7. Remove the 4 Allen cap screws from the sides of the EHA that secure the EHA to the mount. This alows the EHA to be reattached to the optical tube for guide scope use, or you can proceed with further dismantling to degrease the declination clutch. As noted by ???, the EHA is "dimpled" - these dimples are the reason the tube cannot be slipped out of the mount like the '90 and '125. 8. Loosen (but do _not_ remove) the 3 screws that secure the RHS fork to the base. If you remove these screws, you may damage the wiring in the fork arm that runs to the dec motor. Pull gently on the bracket that attaches the EHA to the mount, and it will pop out, exposing the main bearing, declination gear and clutch washer. These can be removed and degreased. As with the other models, I'd recommend an absolute minimum of lithium grease on the rotating parts, and nothing anywhere else. 9. Don't use paper towel on the declination gear - the corners are sharp, and you will get a lot of paper fibres jammed between the teeth - a solvent and an old toothbrush are probably better. 10. Assembly is basically the reverse of this procedure. _I think_ the order for the declination clutch components is (inside to outside) main declination bearing, declination gear, clutch washer with flat side inwards. I'm not sure of this - I didn't know what to expect when I pulled the bracket out - but it matches the wear patterns, and my scope seems to be working fine. 11. You will probably need some thin double sided tape or contact glue to get the rubber feet to stick. Sorry - I just found this out too! bruce
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