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atnbirdie
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Reged: 12/10/06

Loc: Middletown, MD
AZ Motor Control Problem (CPC 1100)
      #5466520 - 10/12/12 08:59 AM

I have my CPC 1100 mounted on a pier in my observatory. I hadn't had a chance to use if for over a month. When I went out to use it last night, I awoke it from hibernation and shortly thereafter, before I could touch another button, the azimuth motor started a runaway slew. The scope is powered with a 30A DC voltage regulator that plugs into an AC outlet (similar to those used for CB sets), and I have checked the power connection pin, etc. on the base of the scope, so this is not an input voltage issue. I also noticed that the pitch of the AZ motor sounded different than normal. Not sure how else to describe it. Speed seemed like a 9, but it was just a bit louder than usual. No grinding, but something was out of the norm.

I took the scope inside where I powered it with a different power cable and freshly charged battery. I re-flashed the HC and MC firmware to the latest versions available. When I powered up the scope and pressed the azimuth button, the scope again slewed at high speed only. It stopped when I released the button, but even when I changed the slew speed to 5, the AZ motor still slewed at what sounded like speed 9 and still had a different sound to it. The ALT motor was however moving at the slower speed. I attempted to do an alignment and as soon as I sent it to the first star, the AZ motor again started a runaway slew. However, my pressing an AZ button on the HC stopped it.

I will check all HC contacts tonight and I have another HC that I can swap out to see if this is a HC issue. However, given the change in motor sound, I suspect it is more likely an issue with the MC board, the motor itself, or both. I will also open the base and check AZ motor and MC board connectors before doing anything else.

Anyone else have an experience like this? Any ideas on how else to proceed to isolate the problem? The scope is out of warranty, so if I need new parts I'll just buy a MC board and/or motor and fix it myself, but would like to minimize my cost so would prefer not to replace both if I don't have to.


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atnbirdie
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Reged: 12/10/06

Loc: Middletown, MD
Re: AZ Motor Control Problem (CPC 1100) new [Re: atnbirdie]
      #5467234 - 10/12/12 06:32 PM

I removed and inspected all connections in the base. All looked fine and clean with no corrosion. Reseated all connectors. Also removed connector boards in base and inspected for corrosion and bridging between connections/lines. Saw none. They were both pristine.

Tried an alternative HC and that had not effect either.

Interestingly, I removed both 4 lead connectors from the motor (one of which I guess is to the PEC control board at the opposite end of the motor shaft from the base). This left only the two single leads that the motor comes with connected and the motor reacted just the same. I could move it in one or the other direction, but the speed was always the same even with both 4 lead connectors disconnected. I wonder if that indicates the motor control board is the culprit? Thoughts?


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atnbirdie
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Reged: 12/10/06

Loc: Middletown, MD
Re: AZ Motor Control Problem (CPC 1100) new [Re: atnbirdie]
      #5468383 - 10/13/12 02:07 PM

Got some advice from Chris in the CPC Yahoo group. It involved going to Utilities/Get Axis Position and seeing what happens when I moved the motors with the direction buttons. Alt numbers changed when Alt motor moved but Az numbers did not. That apparently indicates an encoder problem.

Celestron answered my query in a way that sort of answered my questions and also points to the encoder as the problem. Here it is for your reference as it has some information that may be of use to others in the future:

"looks like you might have a motor/encoder problem. The encoder is a light-emitting diode (LED) device that measures how much the motor has turned. Try this general test of the encoders:

Select UTILITIES-GET ALT-AZ. The LCD display will show lines for azimuth and altitude in degrees-minutes-seconds format. Then select a slow rate by pressing RATE 2. Now use the arrow-direction buttons:

Up arrow - altitude increases sequentially
Down arrow - altitude decreases sequentially
Right Arrow - azimuth increases sequentially
Left Arrow - azimuth decreases sequentially

If the numbers go the wrong way, there is a problem. (Be sure to check SCOPE SETUP DIRECTION BUTTONS as well if they are moving the wrong way to eliminate this setting as the problem.)

At rate 2, the scope moves at the same rate as the sky, 15 seconds of arc per second of time. The numbers in the hand control display refresh about 1-2 times per second. The seconds numbers should change between 5 and 15 between display refreshes. If it is much less or much more than this, there is a problem."

Given I couldn't align the scope so it wasn't tracking, but had NO change in the AZ numbers when I moved the motor with the HC buttons, I'm pretty confident its the encoder so am going to order a motor assembly.


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atnbirdie
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Reged: 12/10/06

Loc: Middletown, MD
Re: AZ Motor Control Problem (CPC 1100) new [Re: atnbirdie]
      #5504619 - 11/04/12 09:35 PM

Just a quick update to say it was definitely the motor. I ordered and installed a new one and all is working fine again.

I do notice the AZ motor sounds different which is not surprising as it is a different motor. However, it seems to have a rhythm to its whirring that I don't recall hearing as much before. However, I guess the proof is in the pudding as after alignment, GoTo was on target.

Is it just me, or might I need to adjust something like the worm gear pressure. I did not change any adjustment in the worm gear so am assuming the sound is just a quirk of the new motor unit.
Steve


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Koen Dierckens
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Reged: 11/04/09

Loc: Antwerp, Belgium
Re: AZ Motor Control Problem (CPC 1100) new [Re: atnbirdie]
      #5504975 - 11/05/12 06:32 AM

Nice exercise in troubleshooting. Thanks for sharing!

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aamilo
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Reged: 02/28/12

Loc: SF Bay Area, CA
Re: AZ Motor Control Problem (CPC 1100) new [Re: atnbirdie]
      #5505578 - 11/05/12 03:11 PM

Quote:

I did not change any adjustment in the worm gear so am assuming the sound is just a quirk of the new motor unit.
Steve




Did you look at the motor movement when the cover was still off?

When I run mine at rate 9 it has a unique rhythm as well. Seeing it with the covers off makes me think it come from the fact that the motor "wobbles" as it turns. It looks like the motor shaft and gear shaft aren't exactly lined up within the coupler. I have been meaning to adjust the coupler to try and remove the "wobble" but it works fine other than the sounds so half of me says don't fix what really ain't broke.


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