Last updated: 4 May 2008
Subject: Applicability of Tuneup Tips for late model ETX-125's Sent: Saturday, May 3, 2008 12:09:32 From: Lorenzo Rota thanks for great site. I have a "late model" ETX-125AT ( 1-2 yrs old vintage ) and was wondering how applicable are the Dr. Sherrod tuneup tips( titles listed below) to newer ETX-125's? Since some of these tips are 5+ years old, I was wondering if maybe the designs were improved to correct these problems?? Mainly I am interested in tips to tighten up the play in DEC and RA axis. I am pretty familiar with the training procedures...so just looking for mechanical tuneup tips. I wasn't clear if some of these tuneup tips only pertained to the earlier models that didnt have the cast aluminum forks. Any clarification is appreciated. Thanks, Lorenzo Rota Performance Enhancement Creating The Perfect "GO TO" ETX or LX 90 Part 1 - Mechanical Considerations and Adjustments German translation (10/04/03) Part 2 - AutoStar Downloads and Post-Download Initialization (10/31/02) German translation (10/07/03) Part 3 - Training the Drives and Celestial Alignment German translation (10/07/03) Part 4 - Eliminating Common "Rocking" in ETX Altitude Axis (9/11/02) German translation (10/07/03) Part 5 - Polar Alignment Position (3/28/01) German translation (10/07/03)Mike here: I'll let Dr. Clay Sherrod, the author of those articles, answer.
From: P. Clay Sherrod (firstname.lastname@example.org) Indeed it would seem to be a "good thing" to update the tune-up tips for the newer metal mounts on the ETX; however, Meade has not only improved the strength, reduced the vibration and increased the longevity of the ETX by going to the newer mount, but they have also pretty much made the ETX mechanically invasion proof. Unless a user has very high levels of understanding of the way that this mount and its wiring are put together, attempting to do something so simple as get to the drive gear and adjust the torque in the DEC axis will pretty much render you a pile of bearings, sleeves, shims and more bearings. Once all the goodies come out, they must be put back together in a very peculiar way (intentionally) in order for the DEC drive to fit back into the fork arm trunions. And the rest of the telescope is even worse for the inexperienced. My rule on the newer metal interior ETX: if you cannot open up something and immediately SEE what you are getting ready to "fix", then leave it alone. Dr. Clay ------------- Arkansas Sky Observatories Harvard MPC/ H43 (Conway) Harvard MPC/ H41 (Petit Jean Mountain) Harvard MPC/ H45 (Petit Jean Mtn. South) http://www.arksky.org/
Thanks to you both for the update. Dr. Sherrod, I did as you recommended for the RA axis in the base....I only opened the bottom for inspection and found the typical "blob of grease" on the RA motor encoder wheel...which I cleaned off. I have not yet inspected the DEC axis. Is it still safe to remove the OTA from the fork and remove the fork covers to inspect the encoder wheel on DEC axis for same problem? Main reason I wanted to check was I had been noticing occasionally a tiny periodic "skipping" when viewing planets and I figured there might be some dirt/grease in one of the encoder wheel slots. Again, many thanks to you both for the great contributions to all ETX users. Regards Lorenzo Rota
Although you can remove the OTA by removing the four hex head bolts, two at each OTA adapter arm, it is not as easy a with earlier models....the OTA does not snap out easily and much care must be taken to keep from breaking the locking pins that secure the front of the OTA to the front portion of the OTA adapters. Nonetheless, you can get it off. Once off, you can remove the covers....all that you need to remove will be the OUTER cover, so this means that you do NOT need to remove the right OTA adapter from the drive unit; this is what can lead to many pieces that unless put back in the proper order, can cause major headaches for you. Once the OTA is removed, unscrew all inner Philips screws from the inside of the right fork arm; this will allow you to separate the outer half from the inner plastic half. Most of what you need to inspect will be exposed from the outside, so no need to remove the inside plate (plastic cover). If you DO need to get to the mechanism in there, you can carefully push the OTA adapter and the trunion bearing shaft out of the fork arm; to do this, you MUST be ready to "catch" all pieces from the inside of the fork arms as they pass out of the metal bearings. I use a screwdriver blade inserted into the opening and they all slide off in the proper order for reassembly once done. When you get that assembly out, keep it all intact and in order. Note that you likely will not be able to simply push all of the components out easily; typically I have to tap on the outside axle using a wooden dowel and very small ping hammer to force the assembly out of the hole (trunion opening). Several very carefully lined up taps will be necessary and do NOT do this without the wooden dowel or you will damage the assembly. Remove the inner plastic half and service what you need to. When re-inserting the OTA and drive assembly back into the fork trunion and bearings, there is a "key" alignment pin in several of the metal components....all of these must align to that pin for the assembly to fit back in. Like I say....a bit of "no man's land" inside these new ones, but it can be done. Proceed slowly and with great deliberation. No need to get in a hurry. Best of luck. Dr. Clay
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