Skywatcher Az GoTo - Intermittent "slow down"

[Macavity]

Skywatcher Az GoTo - Intermittent "slow down".

Having being "overjoyed" with my acquistion of the above, I now find there is an intermittent problem with the Altitude drive in "fast" mode? Essentially, every so often, the motion slows down to a near crawl (or stop). Sursprisingly this doesn't seems to depend on torque applied by the scope weight etc. (My scope is quite well balanced).

Maybe it has to "go back" (to the box-shifter). But I wondered if anyone had seen/solved this problem? On the face of it, it would seems more like a "lack of lubrication" or "something sticking" than fundamental? (As ever, I have had a QUICK "look inside")

Yours, hoping...

[Mikea]

I have noticed this behaviour on the az motion recently. It seems to be intermittent and doesn't affect the positioning accuracy. I had a peep inside and was quite surprised at the small gauge wiring used from the power connector through to a low-current pcb connector. Having said that, I don't believe it's a volt-drop issue. More likely to be mechanical, but I don't know where - I couldn't see anything obvious

[Macavity]

I had a look inside: Not may "user servicable" parts... and not much obvious to go wrong. I notice a slight whiff of "ozone", characteristic of old type electric motors arcing at the commutator? Since miy mount is very new, and I don't think *I* have been the cause of this, I might try to get the supplier to do an exchange... Ah well <sigh>

[sxinias]

I have the synscan Alt/Az goto mount with a Celestron C6S mounted. I also experienced the internment slow down during azimuth slews. The problem was more pronounced during manual slews than during slews commanded by the hand controller. The problem became very acute but like reported, did not appear to impact goto accuracy.

The problem went away as suddenly as it started only to be followed by a far more serious problem .... erratic and uncontrollable azimuth slews. I suspected a loose connection and suggested to my dealer that I open up the mount to see if that were the case. The dealer replied not to do so but to sent it back to them for warrantee service or replacement. The dealer could not repair the mount …. so much for the loose wire theory …. and returned the mount to the UK distributor for repair or replacement. I did not open the mount so I can not comment on its innards.

The mount is new on the street. Let us hope that it does not have any major systematic defects …. the power plug and shaky tripod are enough as it is.

BTW I did solve the power plug issue with my mount by increasing the tripod leg angle from 65 degrees to 70 degrees (used by Meade on their DS2000 tripod). This plus tightening the power plug nut with a pair of needle nose plyiers did the trick. The steeper angle of the legs reduces the power cable’s drag sufficiently to prevent the cord pull-out. I increased the angle by moving the center tray downwards about 10 cm. This also greatly increased the rigidity of the tripod. My tripod is now very stable for its light weight construction and the load I have on it. I improved its stability by tightening all the nuts and bolts, drilling some small holes in the accessory tray and using nuts and bolts to keep it in place, and finially injecting epoxy in the very small cracks between the tripod leg sockets and the legs. This made the tripod steady enough to allow me to extend the tripod legs about 80 percent with out impacting upon goto accuracy. It also reduced the frequency of tripod induced vibration to where it is no longer a major bother when I focus, etc.

Joe

Sxinias

Meade 2045LX3 SCT/DS2000 goto mount

Celestron C6S SCT/SynScan AZ goto mount

Edited August 15, 2009 by sxinias
corrected two typos

[dph1nm]

I know of two Celestron Nexstar SLT mounts which have had to have their Azimuth motors repaired (under warranty) due to erratic motor speed (essentially slowing down then speeding up back to normal speed). As these seem to be similar mounts to the Synscan Alt/Az I wonder if there is a theme developing here ...

NigelM

[sxinias]

Let us hope these are just random failures and not a big gotcha. It would seem that given the number of NexStar mounts sold, that if problem is systematic that the forums would be full of postings. However, as far as SkyWatcher goes, it is too new on the street to have time to establish a track record.

I don't know for sure, but I believe the motors as well as most of the rest of the SkyWatcher AZ mount components are identical with some of the Celestron NexStar mounts. In the PC computer world back in the 1980s, we would call the SkyWatcher a Celestron clone. True there are some differences but mostly appear to be firmware related.

BTW: The Firmware in the version of the SkyWatcher SynScan AZ mount sold in the USA is completely different from that sold in Europe .... in the USA SkyWatcher makes little attempt hide the mount's NexStar origin. see:Sticky: SkyWatcher SynScan Alt/Az GOTO Mount Variants - Astronomy Forum

Sxinias

[profees]

I have just had my skywatcher motor mount completly replaced due to this very problem send it back if its under warrenty.

[Macavity]

Well, being "up to the eyeballs" in other matters re. a recent house move, I didn't get around to contacting the dealer. But there has been a development...

First of all, a quick reminder that in MY case it is the Altitude fast (setting nine) movement that shows the intermittent slow down. But, track it back and forth a few times and it "recovers" (sometimes!). Remove the scope and the problems remains. I became convinced it must be "internal" to the drive - something like a lubrication problem or something "binding".

Doubtless not for the faint hearted or preservation of guarantees. But I opened the housing up again! The SILVER cover is easily removed, by undoing the two Phillips screws. This reveals a load of mechanics, motor and circuit boards. The housing may be left to "dangle" (carefully!) on the power input leads.

Through a window in the casting, you can then see where a small pinion engages with a LARGE gear which controls the altitude. You can see evidence of a significant amount of typical Skywatcher BROWN grease - rather EVENLY distributed around the circumference of the large gear. But it still slows down during parts of the rotation! With no inspiration forthcoming, I decided to try loosening the NUT in the center of the internal housing - this corresponds to the nut at the other end of the gear axis, in the middle of the dovetail clamp. Still no consistent improvement and no obvious source of friction! So I removed the nut completely and pushed on the axis!

Bingo - This allows removal of the circular housing (bearing the scale etc.) containing the large GEAR... At this point, I made an interesting discovery! (If you're still reading thanks for your patience)

To (presumably) cope with the not-inconsiderable LEVERAGE from the scope weight, the inner face of the large gear rotates against three small, circular PTFE(?) "PADS" arranged (and held) equidistant around the circumference of the static housing. But more significantly, and during repeated rotations, the well-greased face of the gear had been swept by the pads, revealing an ring almost free of grease!

So I applied a bit more standard brown machine grease to the face of the gear (particularly onto the "cleaned" area!) and reassembled. The mount now works WELL again... for the moment. I sense the noise from the motor is lessened and certainly sounds less of a struggle?

My conclusion is that THIS was the problem with my specimen of this mount. Quite how long my solution of "adding more grease" will last, who knows! Of course, it seems common practice to re-grease Skywatcher mounts (I did this with my EQ3-2). Lithium grease is also used to advantage as well? If anyone is interested, I can take a couple of camera shots of the parts I re-greased. I can also keep you posted on the longer term effectiveness of this solution.

[sxinias]

Mcavity,

Thanks for the excellent report and so much for my loose connection theory. If not tooooo much trouble, photos would be nice as well as your update.

Question. Were there any issues involved in putting the mount back to gether?

Sxinias

[Macavity]

Sadly, I suspect any plaudits may have been premature...

I left the mount - with my MAK127 attached, overnight, and, this morning, it was "back to it's old tricks". From a cold start the motor again struggled. But, having traversed a region of track, it then moved fairly freely!

I sense I might be barking (meowing) up the right tree but, as yet, have not "cracked it". Perhaps the lottery of (distributor) substitution will get you a "better" example of this mount? For braver souls, removal of the Silver plastic cover reveals:

The above show the NUT you have to remove. Observe and maintain the correct ordering of metal, plastic and compression/split washers! The gear housing has to be "jiggled" to remove (and replace) it. This (presumably) to mesh-unmesh the large gear with the final drive pinion... You then have TWO parts to the assembly:

The Main Mount arm, with the gear housing removed. Here we see the THREE circular "plastic" Pads which form the bearing surface, against the LARGE gear (below)...

The large Gear Housing. This shows the internal face of the Gear, after a few passes over full Altitude range. You can see how the "Plastic" Pads have swept a track clear of excess(?) grease - Or maybe sufficient lubrication?

At THIS point, I'm not really sure how to proceed. I sense(!) I may be "right" re. the nature of the problems in this example of the mount. Clearly, by running the mount for a while "things improve", but this hardly inspires confidence! I must admit I'm a bit disappointed with the whole thing - despite initial promise and GOOD tracking etc.

Maybe a "better" grease would remain(!) between the Pads and the metal surface? Any Experts in lubrication (Tribologists?) out there? Thoughts / Speculation / Inspiration welcome!

[sxinias]

Macavity,

Great photographs. Thanks for taking the time and effort to make and post them.

Maybe my initial hunch that an electrical connection is at fault is worth looking into. Your mount worked fine for a while, then variable altitude motor speed problem. When you opened up the mount and did your first intervention, you could have possibly jiggled a wire or connector and improved the electrical contact. Closed up the mount and it worked for a short time before the loose connection opened up again from vibration, etc.

If you open up the mount again, you may want to take a look at all the electrical connections to make sure that they are firmly in place and making good contact. One culprit is solid wire instead of stranded wire …. Small diameter solid wire can break inside the insulation or at connectors and make an intermittent contact that can be a devil to find. Like I said, I’m just guessing here …….. but ……… back in the early days of personal computers many a repair man made a good living just pulling out boards, polishing the contacts with a pencil eraser and putting the boards back in again.

BTW on the astronomy forum the SynScan goto mount discussion has drilled down to the SynScan hand controllers. Three people who have three different kinds of Skywatcher mounts (azimuth, GEM, and the autoDOB) that use the SynScan Hand controller are experiencing the same failure mode. (In the middle of performing a two-star alignment the controller will simply freeze up. Turn off the power, turn it back on, and the handset says it can't connect with the scope. Turn off the power and push the scope or connectors a little, then turn the power back on, it usually reestablishes a connection. Problem gets so acute that you generally can not complete an alignment, or if you do, the problem occurs soon afterward during a slew.) The only components in common with the three mounts are the hand controller and controller cable.

There is no evidence that the two types of failures are connected but if you make a stretch and assume a common source for the motor speed variation problem and the hand controller lost contact problem you are left with four common items …. the hand controller, the controller cable, the female plug in the hand controller, or the female plug in the mount. Like I said …. an assumption that is a stretch.

Looks like you have the ball on the motor speed variation solution quest now that you’ve opened up your mount. Let us know what you find next. I’m still waiting for the SkyWatcher distribution to come back from vacation

I agree, its begining to look like getting a good mount is like wining the lotto.

Sxinias

Edited August 18, 2009 by sxinias
added comment

[profees]

Cheers for the pictures, when i asked my "good old dad" (who's a qualified enginneer, incase anybody from the shop reads this) to take my mount apart thinking along the same lines i also noticed that the small white pads had been worn unevenly. We re-grease around the motor gears similar to your pictures, unfortunatly for me this did not solve the problem, however it did run more smoothly for a few hours. I would still let your supplier /manufacture know so you have the option of sending it back if need be. Also if you dis-connect the motor from the black mount holdings and run it attached to the PCB but with no strain on it and it still has erratic movement you will know it is the motor (or mototr brushes ) which have worn and need replaceing not the amount of grease you apply.

[rikyuu]

Macavity,

do you have access to a voltmeter or multimeter and can you access the soldered connection of the 2 wires to the motor (not wires going to the encoder sensor)?

Baring in mind the potential for damaging the electronics by making accidental short circuits; I would measure the voltage across the motor when it is slewing normally at max speed and then check it again when the fault occurs. This should show up whether the motor is still being driven or not ie. volts or no volts.

From memory, your pictures look very similar to the insides of the Celestron SLT mount which I have.

I had a problem with that too. It sometimes wouldn't move in one direction.

On mine, the cause appeared to be a fault internal to the motor in which one of the power connections was connected to the body of the motor, I suspected a faulty intenal supression capacitor. Hence in one direction it worked (ie. when one connection was meant to be grounded and the other at a positive voltage), but the other direction didn't work (ie, when the positive voltage was applied to the connection that was inadvertantly grounded).

To determine if this is the case, with the mount powered off, disconnect the power connector from the motor to the circuit board (probably the connector on the top right of your photo). With the same multimeter, measure the continuity from each of the two motor power pins to the metal body of the motor. They should both be open circuit. Bare in mind that as the problem is intermittent, any short circuit between the motor power pins and the body may come and go, so you may have to try it a few times to ensure the fault condition of a short circuit exists.

If it does, then a work around would be to insulate the motor body from the rest of the mount by putting little plastic or paper insulators under the clip, which holds the motor, to isolated the motor body from the clip. This worked for me, but in the end the mount was swapped for a replacement.

I hope this makes sense and helps!

[Macavity]

Thank you ALL for your contributions above. Rather than bore everyone with a point by point answer, I'll just say that it has been fascinating... with one or two hints that we may (occasionally) be looking at the same (albeit hard to pin down!) problem.

With the mount part-disassembled and the "problem" at it's worst, (Drive OK-ish on ONE direction, almost stopping in t'other) last night, I decided to "completely" take apart the ALTITUDE drive chain. And here's what I ended up with... as a sort-of TEST setup:

But IMMEDIATELY it became clear that it was the MOTOR (and attached gearbox) that was varying in speed, and independently of anything I might have downstream (the Pad lubrication etc.)! Indeed the now bare motor performed well in ONE direction, but in the other periodically lost ~40% of it's speed and also sounded "rougher"!

In this state, there are clearly rather few user-servicable bits left - Just a motor and attached "gearbox", which ends in the main drive pinion (visible above!)? There are three small "Phillips" screws on the gearbox, but I was reminded of what happens when you open up a (Grandad's!) pocket watch. Uhm... lots of little gears fall out!

So, with few other possibilities, I tried dripping some "3-in-one" OIL onto the exposed final drive (pinion) SHAFT at either end. Some of the oil was duly sucked up by capillarity... and an improvement was observed! Eventually, I left the motor running continuously in one, and then the other direction (Baader Hyperion in place of Finger!) and over many minutes. I fed it a few more drops of oil, and it then sounded passably (sic) OK.

Conclusion Mk.II (LOL): Along with others here, I sense the problem might be ultimately down to a dodgy MOTOR assembly, which I will ask be replaced (hopefully), if it starts to act-up again. E.G. There's still a music "semi-tone" difference between the forward/reverse pitches and the slower side still sounds a "bit rough" - for however LONG it now works!

THANKS AGAIN though. I sense collectively we also have exposed one or two valuable pieces of information and experience in dealing with this "beast"? And this has certainly been of help (comfort!) to me. It seems perhaps optimal performance is achieved with a combination of working components, each of which has to perform passably well... But most notably the MOTOR itself?

[sxinias]

As you may recall, I had the motor speed problem under discussion that morphed into a more serious problem (azimuth drive, hand controller connectivity, etc.) I sent my mount back and heard from my vendor today. SykWatcher's UK distributor has repaired my mount and it is on its way back to me. The repair was to replace the mother board in the hand controller and provide a new hand controller cable. Will let you know how well it works when I get it back.

If this is truely the fix, then the problem is beyond self-repair.

Sxinias

[MikeWilson]

Hi Macavity,

Did you get a resolution to this issue? Only my mount has just started to exhibit a slight slowdown in the Az.

[Mikea]

Are you still within warranty period?

[MikeWilson]

The mount is around three months old, purchased from First Light Optics, so I guess so?

Edited October 13, 2010 by MikeWilson

[sxinias]

Mike,

Make sure that your telescope is balanced. An off-balanced scope can do what you described. I have an over sized and overweight scope on my SkyWatcher mount a C6S and balance is important.

How to balance? Take the scope off the mount. Install a 25 mm eyepiece. put a pencil on a table and place the telescope on top of the pencil at a 90 degree angle with the vixen dovetail resting on top of the pencil. Move the scope until it balances on top of the pencil (actually you can't perfectly balance it but you will see where the balance point is located). Put a mark where the balance spot is on your dovetail. (I used silver fingernail polish to make it easier to see in the dark). When you install the telescope make sure that the mark on the dovetail is centered in the mount's dove tail saddle.

If that does not solve the problem, then before your warranty expires, contact your dealer for warranty service. I had to do that with my mount soon after I received it last year. It has been well over a year since SkyWatcher repaired my mount and it works great. I have used it very much and even have put an 8 inch SCT on it for a while. The cause of my mount's failure was the hand controller mother board. SkyWatcher said that they replaced the mother board but I suspect they just sent a new mount as some scratch marks mysteriously disappeared.

Goto accuracy of the mount is excellent as long as you keep all the nuts and bolts on the tripod tightened. There are some other things to do to reduce the vibration caused by the tripod such as epoxy between the legs and mount's leg sockets, lowering the accessory tray, etc.

Joe

[Mikea]

The mount is around three months old, purchased from First Light Optics, so I guess so?

OK - so resist the urge to "tinker" and ask FLO to send it for repair. I had mine fixed within warranty - it came back working perfectly and has done so ever since. I have also done the epoxy mod mentioned by Joe which improves the tripod stability quite dramatically ( I did that AFTER my warranty ran out!)

[Macavity]

I would tend to ask for an exchange. I recall the company (not FLO!) I bought my first Synscan from is now (well) "bust" and I DID quite a lot of semi-destructive testing on the mount.

Re: Synscan: Basically an (intermittent) MOTOR problem - Quality control, perhaps? Even my new IOPTRON mount (At four times the price!) has a slightly dodgy (motor) record and people often routinely replace bits of it (bearings etc.) to get even BASIC reliability...

OK, but would you buy a used CAR off yer average telescope mount manufacturer?

Edited October 14, 2010 by Macavity

[MikeWilson]

I suppose mounts, bring a niche product, means that the manufacturers can get away with a lot more - on the basis that the customer is typically expected to do their own maintenance?

In any case, FLO are arranging for the distributor to collect. Not sure what happens next, fix or replace?

Thanks for the thread (and the tear down pics!).

[AdeyG]

Hi Guys,

This sounds just like a problem i had with my 5SE mount. I had done all the things mentioned above, checking tightness, grease etc!

What i eventually found was that even when the motor was removed from every thing it was still slowing down! So i sprayed some switch cleaner onto the motor com and brush end.

Problem disappeared and so far (fingers crossed) hasn't returned.

As an extra i also replaced the cheap plastic washer and spring washer with a proper thrust bearing.

cant post pics (is there a minimum post limit?)

Clear skies

[AdeyG]

Here are the pics of the thrust bearing used to replace the original plastic washers on the nexstar 5SE mount.

They were fitted to both axis and so far have proved to be free running.

Clear skies

[MikeWilson]

Interesting pictures. Where did you find the replacement washers? B&Q? (sorry, I'm a DIY dunce!).

FLO have arranged for the distributor to collect tomorrow, so my mount head is waiting for pick-up.

Since they've given me good service I've just placed an order for a new guidescope, mountings and standalone guide camera with them