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AVX - Have you seen this motor behavior? - Need Advice

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#1 Jim Thommes

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Posted 16 September 2020 - 06:58 PM

OK, this has happened to me twice now - first with the DEC motor; most recent with the RA motor...

 

The beginning of a session; turn on the mount; go to the align process; DEC axis motor doesn't run - crickets. No sound whatsoever on that motor. Cycle the mount power - no change - RA motor runs as expected the DEC is silent. Take off the motor board housing - inspect - nothing looks awry. Re-seat internal connectors - no change. After an hour of retrying these steps -no change. Pack it in for the evening take the mount off the observatory pier to troubleshoot at home. Two days later, get the mount ready to troubleshoot,  ....And... the mount motors work perfectly!!

 

With nothing more to do on troubleshooting, take the mount back to the observatory. It works flawlessly for several months and many sessions.

 

Last session out, the RA motor does the same thing - crickets - while the DEC motor runs as expected. Follow the same steps as before but no joy. I even check the motor board fuses - they all read intact. Take the mount home to trouble shoot . This time I try trouble shooting the next day (about 18 hours after the initial failure and again about 22 hours) - the failure persists - the RA motor is silent; the DEC motor runs fine. I even tried resetting to the factory defaults - no change.  I get a good nights sleep. Next morning (about 40 hours after this last failure) I gather some troubleshooting tools (meter, clip leads, etc). I power up the mount prior to begin trouble shooting,  ...And... the mount motors work perfectly!!!

I have mixed feelings of relief and frustration.  I haven't taken it back to the observatory yet, but I expect the motors will run fine.

 

I have had this AVX since 2014 and it has been my secondary (small refractor) astrophotography work horse setup since then - working pretty much flawlessly. So I got to thinking about "what has changed" during this summer when these two problems occurred?  I have used this mount connected to the same computer. The mount gets commands from SGP and PHD2 as well as a planetarium program (first The Sky, now Stellarium). Here is what has changed:

 

1. I updated the Celestron mount ASCOM driver for the mount before the first failure. This is the update that fixes the  SGP centering accuracy (includes time offsets for goto from a single direction). This was a pretty mild update. I don't expect this is the cause.

 

2. I did start recently checking all my connections to my laptop (camera, FW, guide camera, focuser, and mount) in daylight prior to the evening session just as a pre-check. For both failures,  I inadvertently left the PC connected to the HC RS232 port when I powered down the mount. The three PC apps were still connected to the mount at mount power down and stayed that way for an hour or so (while the apps were presumably pinging for a connection or issuing commands to an un-powered RS232 port on the mount's HC). I know RS232 ports are notorious for sneak path powering of internal circuitry. I can't tell if that is happening here or if the mount HC and/or MC firmware are responding in an unintended manor to this condition.

 

I suspect item number two above is the root cause - but it is unproven. It could be that some internal Firmware feature is setting some timeout that persists at power cycle. That timeout  being somewhere between 22 and 40 hours). The problem is that I can try to repeat and confirm this mode, but it shuts me down for something between 22-40 hrs.

 

Questions:
1. Has anyone else experienced similar failure and then miraculous recoveries?
2. I would love to prove root cause, but I am not willing to try to re-create an undesired operational mode that is unaffected by power cycling (or anything else I tried). Does anyone know if there is an internal reset pad or jumper that sets a "pristine" condition for the next power up (so I don't have to wait 22-40 hours to run again)? Does anyone know if I pull the lithium coin battery for a sufficient period if this creates a "pristine" condition that allows me to restore motor operation at next power up?

Helpful information: HC firmware 5.21.2336; MC firmware 6.07



#2 Michael Covington

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Posted 16 September 2020 - 07:32 PM

Check your 12-volt DC power -- this sounds like it might be a case of low voltage.

Also check the button cell battery inside the mount.  Although that shouldn't have anything to do with this problem, it will eventually need replacement, and if it's low, settings might vary randomly.



#3 tonyt

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Posted 16 September 2020 - 08:46 PM

I had trouble with my AVX once and cleaning the cable and mount contacts with alcohol on a Q-tip fixed it.



#4 Tom Stock

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Posted 17 September 2020 - 06:32 PM

OK, this has happened to me twice now - first with the DEC motor; most recent with the RA motor...

 

The beginning of a session; turn on the mount; go to the align process; DEC axis motor doesn't run - crickets. No sound whatsoever on that motor. Cycle the mount power - no change - RA motor runs as expected the DEC is silent. Take off the motor board housing - inspect - nothing looks awry. Re-seat internal connectors - no change. After an hour of retrying these steps -no change. Pack it in for the evening take the mount off the observatory pier to troubleshoot at home. Two days later, get the mount ready to troubleshoot,  ....And... the mount motors work perfectly!!

 

With nothing more to do on troubleshooting, take the mount back to the observatory. It works flawlessly for several months and many sessions.

 

Last session out, the RA motor does the same thing - crickets - while the DEC motor runs as expected. Follow the same steps as before but no joy. I even check the motor board fuses - they all read intact. Take the mount home to trouble shoot . This time I try trouble shooting the next day (about 18 hours after the initial failure and again about 22 hours) - the failure persists - the RA motor is silent; the DEC motor runs fine. I even tried resetting to the factory defaults - no change.  I get a good nights sleep. Next morning (about 40 hours after this last failure) I gather some troubleshooting tools (meter, clip leads, etc). I power up the mount prior to begin trouble shooting,  ...And... the mount motors work perfectly!!!

I have mixed feelings of relief and frustration.  I haven't taken it back to the observatory yet, but I expect the motors will run fine.

 

I have had this AVX since 2014 and it has been my secondary (small refractor) astrophotography work horse setup since then - working pretty much flawlessly. So I got to thinking about "what has changed" during this summer when these two problems occurred?  I have used this mount connected to the same computer. The mount gets commands from SGP and PHD2 as well as a planetarium program (first The Sky, now Stellarium). Here is what has changed:

 

1. I updated the Celestron mount ASCOM driver for the mount before the first failure. This is the update that fixes the  SGP centering accuracy (includes time offsets for goto from a single direction). This was a pretty mild update. I don't expect this is the cause.

 

2. I did start recently checking all my connections to my laptop (camera, FW, guide camera, focuser, and mount) in daylight prior to the evening session just as a pre-check. For both failures,  I inadvertently left the PC connected to the HC RS232 port when I powered down the mount. The three PC apps were still connected to the mount at mount power down and stayed that way for an hour or so (while the apps were presumably pinging for a connection or issuing commands to an un-powered RS232 port on the mount's HC). I know RS232 ports are notorious for sneak path powering of internal circuitry. I can't tell if that is happening here or if the mount HC and/or MC firmware are responding in an unintended manor to this condition.

 

I suspect item number two above is the root cause - but it is unproven. It could be that some internal Firmware feature is setting some timeout that persists at power cycle. That timeout  being somewhere between 22 and 40 hours). The problem is that I can try to repeat and confirm this mode, but it shuts me down for something between 22-40 hrs.

 

Questions:
1. Has anyone else experienced similar failure and then miraculous recoveries?
2. I would love to prove root cause, but I am not willing to try to re-create an undesired operational mode that is unaffected by power cycling (or anything else I tried). Does anyone know if there is an internal reset pad or jumper that sets a "pristine" condition for the next power up (so I don't have to wait 22-40 hours to run again)? Does anyone know if I pull the lithium coin battery for a sufficient period if this creates a "pristine" condition that allows me to restore motor operation at next power up?

Helpful information: HC firmware 5.21.2336; MC firmware 6.07

YES.

 

In my case, the pins inside the RJ45 jack for the DEC motor were "tired" and had lost their spring. Using a small hooked pick I pulled each pin out a bit to make sure there was good spring contact against the male plug terminals. I discovered this by wiggling the cable at the port.

 

For the RA, I am not sure. Maybe the hand controller port has the same issue?

 

When you examine the controller board, use a magnifying glass and a flashlight. Look for any cracks in the solder joints for the port socket pins. Look for rings around the pins indicating stress has broken the joint.


Edited by Tom Stock, 17 September 2020 - 06:54 PM.


#5 Jim Thommes

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Posted 17 September 2020 - 06:58 PM

Check your 12-volt DC power -- this sounds like it might be a case of low voltage.

Also check the button cell battery inside the mount.  Although that shouldn't have anything to do with this problem, it will eventually need replacement, and if it's low, settings might vary randomly.

 

 

I had trouble with my AVX once and cleaning the cable and mount contacts with alcohol on a Q-tip fixed it.

Thanks Michael, Tony. I appreciate the responses.

 

I probably should have been more emphatic about the PC connection issue. ...

 

Twice I have forgotten and inadvertently left the HC RS232 port on the AVX connected to the PC with active apps connected to the AVX when I powered down the AVX. I (again inadvertently) left the setup in this state for an hour or so. Each time this active connection was left on the un-powered AVX,  a motor did not operate upon powering up the AVX again. Once it was the DEC motor and once the RA motor that was silent and did not run for the rest of the evening session. The only times the motor have not worked on this AVX was when I inadvertently left this connection in place. This was a 100% correlation in both directions (admittedly only a sample of two). What I don't have is a validated root cause for this correlation. Obviously I will endeavor to  not make this connection again unintentionally. I don't want to wait the 20+ or so hours to have the quiescent motor become active again.

 

When these incidents did occur, I cleaned off and re-seated cables connectors both internal and external; checked power (17 AH battery - 12.95 volts); cycled power; performed factory reset. None of these had any impact. If I waited 20+ hours, the problem resolved.

 

I was looking at the Nexstar Resource site and see some interesting information about HC communication to the two motor controllers (and among other things like AUX Ports, RTC, GPS, etc). These all share the same communication channel and that the RS232 port essentially is this same channel with RS232 buffers on the front end.  So my inadvertent active connection to the HC RS232 port upon AVX power up may be disrupting initial communications to the Motor Controllers. I will contact this site to see if they have any more information or insight.

 

So What I really want is a process that allows me to remove the long wait time to have the motor operate again. The site suggests that a non-working MC may be in "boot mode". Reloading the AVX FW in some cases is needed to solve the "boot mode" condition. This was in the "No Response" (error 16 or 17) article. I want to ask them if this seems like a potential approach to doing an immediate fix to my issue without having to wait the extended time to recover.


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#6 Jim Thommes

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Posted 17 September 2020 - 07:13 PM

YES.

 

In my case, the pins inside the RJ45 jack for the DEC motor were "tired" and had lost their spring. Using a small hooked pick I pulled each pin out a bit to make sure there was good spring contact against the male plug terminals. I discovered this by wiggling the cable at the port.

 

For the RA, I am not sure. Maybe the hand controller port has the same issue?

 

When you examine the controller board, use a magnifying glass and a flashlight. Look for any cracks in the solder joints for the port socket pins. Look for rings around the pins indicating stress has broken the joint.

Thanks Tom, I will take a close look. Please see my earlier post (I think we crossed in our posts). I did actually measure all of the motor fuses to verify they were intact. When I did so, I was looking closely at the MC board - but with just my magnifying readers (no magnifying glass). Thinks looked OK at that scale.  If I do not resolve the issue by reloading the FW (if it happens again, or I try to force it with my connection conditions), I will make an inspection. If history repeats, I will have 20 or so hours to do it wink.gif.

 

So what actually happened when you wiggled the cable in the port? Did the DEC motor operate intermittently? I ask, because abolutely any thing I did to connectors made no difference. But after I waited the requisite time (having done nothing else to connectors since the last time when the motor wasn't running), the motor and whole AVX mount ran flawlessly regardless of any wiggling I subsequently did on the connectors.


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#7 Michael Covington

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Posted 17 September 2020 - 07:20 PM

Have you been to teamcelestron.com?  If not, now is the time... That's where you can communicate directly with the Celestron engineer who designs these things.



#8 Jim Thommes

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Posted 18 September 2020 - 06:23 PM

Have you been to teamcelestron.com?  If not, now is the time... That's where you can communicate directly with the Celestron engineer who designs these things.

I have not yet. I did not know of this resource.

 

I did access the site. I guess I should just register then post my issue? I will do so and respond to this thread again if I get a response or resolution.


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#9 Tom Stock

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Posted 19 September 2020 - 08:39 PM

Thanks Tom, I will take a close look. Please see my earlier post (I think we crossed in our posts). I did actually measure all of the motor fuses to verify they were intact. When I did so, I was looking closely at the MC board - but with just my magnifying readers (no magnifying glass). Thinks looked OK at that scale.  If I do not resolve the issue by reloading the FW (if it happens again, or I try to force it with my connection conditions), I will make an inspection. If history repeats, I will have 20 or so hours to do it wink.gif.

 

So what actually happened when you wiggled the cable in the port? Did the DEC motor operate intermittently? I ask, because abolutely any thing I did to connectors made no difference. But after I waited the requisite time (having done nothing else to connectors since the last time when the motor wasn't running), the motor and whole AVX mount ran flawlessly regardless of any wiggling I subsequently did on the connectors.

Ok thats interesting. In my case wiggling the connector made the motor stop and start.

 

When something starts working or stops working after a certain amount of time my first thought is bad solder connection or failing component.  As things warm up they expand and either make a connection or break a connection, whether on the PCB or internal to an IC.

 

When you power on the mount and it's not working, grab a hair dryer and try warming up the main board by blowing warm air into the ports ... see if it does something different.

 

Also try tapping sharply on the housing with the handle of a screwdriver or rubber mallet while slewing... see if it hiccups. If so you have a bad solder joint somewhere.

 

What happens if you wiggle your power connector? I'm wondering if it's making enough contact to get the computer up and running, but not enough to provide sufficient current to the motor driver. If this is the case spread the center post slightly with a small screwdriver.

 

Maybe someone with more electronics experience will chime in. I'm just a repair hobbiest.


Edited by Tom Stock, 19 September 2020 - 08:43 PM.

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#10 Jim Thommes

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Posted Yesterday, 07:46 PM

So one of my astronomy buddies had an interesting theory. ...

 

A while back, Fter working on his  Ford pickup's engine, the engine idled poorly and would not stay running. When he got in touch with a service tech at the dealership, his response was:

 

"Yeah, that happens occasionally. when the engine is serviced. We think there is a capacitor in the ECU computer that sometimes doesn't have a discharge path after reconnecting the ECU. Wait for a day or so and the charge will bleed off."

 

Sure enough, he waited until the next day and his pickup started and idled fine.

 

This actually better matches all the behavior I have seen when this anomaly occurs on my AVX. I will try to pursue this idea with Celestron

 

So obviously my immediate approach is to be very careful with the connection of the mount HC to the PC (i.e. do not leave it connected when the mount is powered down). When I do this, I am golden. But... all I need to do is to forget once, and that night's session is done. Long term, I want to avoid this. Doing an inadvertent action that is not correctable right away (but need 20 plus hours to recover on its own) certainly kills the nights imaging/astronomy.

 


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#11 Michael Covington

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Posted Yesterday, 08:41 PM

That is very interesting.  Microcontroller failing to do power-on reset because it was powered by a capacitor that didn't discharge when it should.

Maybe they got higher-grade capacitors than they used to get...

 




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