Last updated: 19 September 2005
Subject: Technical Memo to Help ETX-60AT Users Repair non-working Azimuth Clutch/Worm Gear Sent: Friday, September 16, 2005 18:58:06 From: Christopher Scheer (email@example.com) Had a problem with my ETX-60AT I purchased, worked great for a year, then moved to Florida and stored it for a few months. When I took it out and set it up, the azimuth clutch did not engage no matter how hard I tightened the adjustment lever. Upon reviewing the following posting that I found in a link on your etx site, http://www.weasner.com/etx/techtips/Cooney_70AT_Guide/70atguide.htm I found a couple discrepancies with the model I have and to 70AT mentioned. To wit, the worm gear transmission assembly on my 60AT was NOT spring-loaded; in fact there were basically just two stantions risng perpendicular from the slag metal base that acted, or at least were supposed to act, like a tensioning bar to the worm gear assembly to tension it to the azimuth drive gear. These had either just worn apart a bit or the plastic housing to the worm gear assembly had worn to the point that they did not provide enough tension to hold the worm drive assembly tight against the clutch gear. I employed the following method to resolve the issue satisfactorily: Problem: ETX-60AT azimuth drive does not turn the scope (engage at all) Symptom: Drive clutch tightening lever is tightened as much as feasible, azimuth drive is heard turning/functioning, but scope does not revolve, in addition scope can be turned by hand no matter how tight the clutch level is applied. Materials: Basic hand tools (screwdrivers, medium/small phillips head, socket set w/ 18 mm and 3/8 inch sockets, needlenose pliers, exacto knife, etc) approx. 4-5 feet of 4 lb. nylon fishing line (MUST be 4# test) small tube of lithium grease sandpaper Steps: Note: Some authors have described the plastic housing nut, (which has 4 posts on the top of it to secure the primary clutch washer nut) as an "epoxied" non-threaded nut which needs to be sheared off the unit and re-engineered. This was not the case in my scope, the plastic nut was in fact 'outside threaded' to the housing and I was carefully able to unfreeze and remove it with an 18mm socket. This saved a substantial amount of "re-engineering". Disassemble the base of the scope as instructed in the above link. Perform the basic maintenance (clean, sand the center slightly, then re-lube clutch gear (teeth only). Remove excess grease from the worm drive assembly, if evidence of plastic bits from wear or manufacturing process is evident, then clean the entire assembly carefully with 90% isopropyl alcohol, let dry, and re-lube LIGHTLY all moving parts only with lithium ("white") grease. Don't use stronger solvents to clean the plastic gears (for obvious reasons). Note: Some authors have described the plastic housing nut, (which has 4 posts in it to secure the primary clutch washer nut) as an epoxied nut which needs to be sheared off the unit and re-engineered. This was not the case in my scope, the plastic nut was in fact 'outside threaded' to the housing and I was carefully able to unfreeze and remove it with an 18mm socket. This saved a substantial amount of "re-engineering". Remove the battery pack from the unit (unplug the entire pack from the 9V connection. Check the back and forth "play" on the azimuth worm gear transmission assembly; you may notice (as I had) that there really was no longer any, or at best very little, tensioning of the worm gear assembly towards the axle in the base. It pretty much moved back and forth freely. If this is the case, then perform the following repair to re-tension the worm gear assembly to the clutch gear: 1) Cut an approx. 12 inch piece of the nylon fishing line (must be approx. 4# single-thread nylon, which provides both the correct amount of tensioning as well as being extremely stable to any lubricants, solvents, or anything else including of course dew/water.) 2) Pass the line through the battery pack housing and tie off tightly to the battery housing. You will be connecting the other end to the small plastic hook on the top rear of the worm gear drive; I passed the line from the 'long end' opening of the batter compartment through the corner opening (for the power 9V connector lead to pass through) in order to keep the tensioning line "out of the works" of the rest of the assembly so-to-speak. 3) Measure a couple inches past the small plastic hook on the rear of the worm gear assembly (this hook appeared to have been engineered to hold the drive assembly back out of place against the third stantion during the manufacturing process; I could find no other engineered use for it) and cut the excess line off. The line should be running in the shortest path between the two points. MAKE SURE you've already moved the worm gear assembly to its innermost position (closest to the center of the base). 3) Make a small slip knot loop from the end and tighten the loop around the small plastic hook on the top rear of the worm gear assembly. 4) Taughten the line as much as you can and tie it off with NO slack whatsoever. I simply used three slip knots reversed to get a good non-slipping know. REPEAT the above steps (1-4) a second time; this will provide enough tension to keep the worm assembly firmly against the clutch gear BUT also enough stretch to allow you to replace the base and re-engage the worm gear to the clutch gear without too much difficulty. I put a third tensioning line in as a precaution. (In case one broke) At this point it's time to re-assemble. Reassemble the lower base (which holds the clutch gear) to the top of the base (worm gear assembly) by first pulling the worm gear assembly towards the outside rim of the housing. You may have to experiment a few tries, but you should be able to find the right place to stretch the tensioning (fishing) lines to, to allow you to re-attach the clutch gear base and then get the worm gear firmly engaging the clutch gear. The fishing line will not snap back immediately, so this allows a second or two to get the bottom base re-attached to top with all gears engaged. Once you have the clutch base re-attached loosely to the upper base, you can use your finger or a pair of needlenose pliers to reach into the battery compartment and further tighten the fishing tensioning lines and make sure the gears are firmly engaged. (Be careful with pliers; 4# test will cut easily on steel). Re-assembly the clutch mechanism , adjust the tension level settings/bolt to optimal levels as described in the above link, and test the azimuth with the clutch engeged (tightened); you should now once again have azimuth control. Important to remember, run through the drive motor training steps and reset step as recommended and described by Meade to get the electronics/drive back in optimum working order/adjustment once the scope is reassembled completely. Hope this helps someone out there; I've found the ETX site an absolute treasure trove of information on this great series of amatuer scopes! Thank you, Chris Scheer CSC Computer Sciences Corp. GPES UNIX Support Team-Carrier/UTC
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