Last updated: 31 October 2012
This page is for user comments and information specific to the Meade ETX-90RA (originally known as the "ETX Astro"). Comments on accessories and feedback items appropriate to other ETX, DSX, and DS models are posted on other pages. If you have any comments, suggestions, questions or answers to questions posed here, e-mail them to me for posting. Please use an appropriate Subject Line on your message per the Site Email Etiquette. Thanks. Remember, tips described on this site may invalidate the warranty on your telescope or accessories. Neither the submitter nor myself are responsible for any damage caused by using any contributed tips.
Subject: ETX-90RA RA Slew problem Sent: Tuesday, October 30, 2012 12:47:17 From: John Deriso (firstname.lastname@example.org) When resting on the scope base, the RA motor turns the scope smoothly. When tipped for polar align, such as with the table-top tripod legs set to 39 degrees, there's a click and a slight jump in RA every 9-12 seconds. The RA clutch engages firmly and is not at end of travel. I opened the base and disassembled to study the clutch mechanism and gears. No apparent wear of plastic gears, the motor shaft and gear are sound. Motor is firmly mounted. Tried adjusting the tension of the single bolt that holds the plastic base together on the RA axis. If too tight, RA won't move. If too loose, the base halves wobble sloppily. I adjusted tension until RA rotation barely binds. Re-assembled, still clicks and jumps. Same problem whether in N or S hemisphere switch position (motor drive reversed). Significant stiction when tipped for polar align and rotated manually, but much less stiction when resting on scope base. There's a clue here somewhere, I think the click and jump are caused by the stiction. Suggestions? Lubrication? John DerisoMike here: My first thought would be the small Teflon pads around the interior circumference. One or more could be missing or worn.
That occurred to me too, Mike, right after I sent my post. I find 3 positions for pads, 120 degrees apart. Two are missing a pad, and there's a black "pad" in the third position. It can be "wiggled" slightly, so it's probably adhesive-bonded. I see online there is such a thing as black Teflon. I'll take it from here, thanks. John
Subject: re: Can ETX90-RA voltage regulator survive 5 volts input rather than 4.5 Sent: Saturday, October 27, 2012 18:54:45 From: richard seymour (email@example.com) If you have a 5v supply, you could put a diode forward-biased in series with it. The diode will have a near-constant forward voltage drop. Pick one that can handle the expected current (2 amps should do) and that has about a half volt drop. That will bring your 5v supply down to the scope's wishes. (where are you getting a 5v supply? Many "wall warts" are unregulated, and will drift up to as much as 1.4 times their "rated" voltage. Doing a little catalog digging, i see that Radio Shack sells a two-pack of 1N5402 3 amp diodes... unfortunately they have a 1 volt forward drop. Visiting Digikey, i see that a 1N5821 would do... it'll handle 3 amps, and drops a half volt at that current. They're only 46 cents each, but Digikey has (if memory serves) a $25 minimum order. http://www.digikey.com/product-detail/en/1N5821-E3%2F54/1N5821-E3%2F54GICT-ND/190178 Continuing the search, i'm getting the impression that you'll need a Schottky diode to achieve the half volt drop (normal silicon diodes have a full volt drop). Newark Electronics or Jameco may have more reasonable ordering policies. You could also check locally to see if there are electronic supply houses with pick-up desks or retail store fronts. good luck --dick
Subject: Can ETX90-RA voltage regulator survive 5 volts input rather than 4.5 Sent: Thursday, October 25, 2012 06:49:27 From: Mike Corley (firstname.lastname@example.org) I have just purchased an older ETX90-RA from a chap that never looked at the bottom and so did not even know there were batteries in there. As you would suppose, there were a group of very corroded batteries in the battery case. I have been able to clean up the mess. I have the motor running. I have looked at the small controller box with the toggle and two momentary switches and intend to replicate it. My real concern is if I can replace the use of batteries (the bane of electronics) and use a 5 volt power supply? I lean toward the belief that an extra half volt could not possible harm it, BUT in this case it does represent almost a 10% overvoltage. What are your thoughts? Steven Corley Waller, TexasMike here: I would be cautious about overvoltage. The electronics in the ETX are rather fragile. But you have an interesting project; keep me posted. It would make a great Tech Tip article.
Subject: Complete disassembly of an ETX Astro 90 Sent: Thursday, October 4, 2012 17:24:52 From: Zygmo (email@example.com) I have just acquired an Astro 90 that is absolutely filthy. Inside and out! It had been stored for years with no caps on either end, and the batteries still installed, of course. It looks like I will have to do something about the circuit board, as well as clean everything up. By the way; surprisingly, the optics and other parts appear to be scratch-free...cleaned up, I think it will look good as new. Of course, I had to remove the baffle from the mirror on the corrector plate...it had shifted about a third of it's diameter. The glue and tape removed fairly easily, without any damage to the glass. I have read the directions on your site on how to reinstall it. My question is....where can I find instructions on how to completely dismantle this scope for cleaning? I see on your site several individual sub assembly instructions, but not necessarily specifically to the Astro 90. For instance, are instructions on removing the tube assembly universal for all ETX 90s? Also, since this only drives in R.A. without GOTO, does that mean the circuit board is only a power supply, and the telescope motor could just be controlled by a universal power supply having the same voltage and amperage as the three batteries, or are there speed control pots on the board? I can't afford to spend much on this, so I need to be able to do everything myself. Thanks for any help on this. I have other scopes and your site has been invaluable for information. DeanMike here: The ETX-90RA mount and circuitry is different (but similar in some respects) from the ETX-90EC/AT models. But removing the OTA is the same remove the two screws on both sides of the ETX where the tube adapters are located; then carefully expand the fork arms to release the small plastic tabs on the tube adapters. For cleaning the optics, see the article "Cleaning Optics" on the Helpful Information: Buyer/New User Tips page. If you need to replace the circuit board, try Telescope Warehouse (link on the Astronomy Links page).
Ok. Thanks. I did not get back to my mail till just now, but I went ahead and removed the OTA last night. It came off fine. I dismantled the OTA, and was surprised to find the main mirror clean enough. The flip mirror, and corrector were filthy though. I hate cleaning the secondary mirrors on ALL telescopes because as far as I have seen, none are overcoated with Silicon Monoxide. Having no choice, though...I washed all the back, including the flip mirror. Flip mirror cleaned as good as can be expected....the rest nicely. The OTA is back together, with everything but the Secondary baffle on. Am picking up some two part Epoxy today. I did look through the scope this morning, though....nice and clear, with a slight bloom on one side due to the lack of the baffle, I assume. However, I think I forgot to mention yesterday that the eyepiece tube was inserted crookedly. REAL crookedly! I had to tap one side several times from inside (scary!), and it may not be exactly right, so that could explain the bloom too. I will work on that some more, after I install the baffle. The battery holders and some of the circuit wires were green from the battery leakage. The motor did not operate after I cleaned that and installed the batteries...however, I did discover something there too. All I had were some standard non-alkaline batteries. While working on this scope last night, I decided to take some pics of the parts with my digital camera, which reported bad batteries when I turned it on. I removed the new batteries from the scope, installed them in my camera, and the camera reported "No Batteries". Checked them with my meter, which reported full charge. Put them back in the camera, which again said "No Batteries"! I had two expensive batteries for my other camera, installed them in the camera, and it worked perfectly. So, I will also buy some good Coppertop batteries today, and try the scope motor again. Maybe I will luck out! Will let you know. I have one more question, please. I would like to remove the fork arms to be able to take them apart for cleaning too. When you remove that silly self tapping screw under the circuit board, does the top just lift off then? Nothing going to go flying off in the distance never to be seen again...right? And while it is apart, can you direct me a post that will come closest to telling me what to do while I am in there? Thanks for all your help. I have far better scopes than this one can ever be....but I like the challenge of restoring it, and the portability of this scope could be handy.Mike here: Thanks for the update. Glad things are going well. There are many disassembly articles on the Helpful Information: Telescope Tech Tips page. And while we're discussing disassembling, be certain to read the Disassembly Procedure article there. And while you're documenting everything you do, if you want to write it up (with photos), I'll be happy to post it so that others can benefit from your experience. Thanks.
Subject: Basic ETX-90 Sent: Saturday, September 22, 2012 12:35:28 From: firstname.lastname@example.org (email@example.com) Hi Mike - today at the flea market in Glendale I purchased a used ETX-90 - an EXT-90RA based on info gleaned from your website. No tripod, no Autostar. I had to find the manual online to discover where the battery compartment was hidden. 3 AAs still installed with one battery clip fully corroded. Removed the PC board, de-soldered the leads from the motor, de-soldered the offending battery clip and cleaned it up. Put it back together. The OTA is currently away from the fork unit and I may keep it that way and use it on an EQ mount when I want a quick look at something., Had I not found your mighty websites while I was waiting for my LX90-10" last spring I'd not known anything about the scope. At least I had knowledge when I saw it sitting on the table this morning, and knowledge on where to start looking to I.D. this scope. Another success story! Moe
Subject: your help please Sent: Friday, September 21, 2012 09:52:28 From: Carl Weil (firstname.lastname@example.org) i just got a old broken side arms ra90 meade with missing top eyepiece assembly and have found new arms but dont know how to open botom canaster it was made in 1997 - can i purchaser a instruction manual or help from you? Sincerely, Carl Weil, DirectorMike here: Apologies for the delayed response. Please see the Announcements: Site page on the ETX Site for more on email. Also, PLEASE read the Email Etiquette page on the ETX Site. Your message was originally deleted UNREAD as SPAM due the Spam-like subject line. Thanks for understanding.
I was able to get bottom plate off by gently hitting with hamer when unit was inverted was unable to pry off earlierMike here: Glad you got it off. Odd that it took a hammer.
please what epoxy would you recommend to hold top lens holder in when i get one? there is a hair line crack in the plastic housing at the lens holder holeMike here: I don't have a recommendation. Try searching the ETX Site for "epoxy" or "glue". You don't want to use a glue that can outgas and coat the optics.
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