Problem with abrupt declination swings


Lately, I have been experiencing abrupt declination swings during event sessions. I do not know if the mount, SGP or PHDII are the cause. Tracking is quite good in between these anomalous events.

Can someone please help. Attached please find an SGP debug log. A declination shift event occurred at 19:38 hrs. Attached also please also find a screenshot of phd guiding graph.

sg_logfile_20150716183005.txt (196.7 KB)

Many thanks,

Flarestar Observatory
MPC Code:171


Are you using the same mount (NEQ6 Pro) and scope (Meade 10" SCT) as shown in your web site? If so, your large scope along with guide scope may be too heavy for your mount for imaging. It’s also possible that your mount is starting to get stiction and may need maintenance.

You might want to upload PHD 2 Guide and Debug logs as well.



Thanks for your reply. Yes it’s the same mount. I never had problems before. Can do 10 minute exposures at it’s native F/6.3 configuration. These anomalous events only happen once or twice occasionally. So the problem is not continuous.

Regarding stiction, I do not know but mount (NEQ6) is just less than 1 1/2 years old. Does it already need maintenance? It performs remarkably well in between these events.

I’m attaching an excerpt of PHD2 log.

PHD2_DebugLog_2015-07-16_185722.txt (710.2 KB)



Since there is no continuous tracking for Dec axis, it’s also possible that in most cases when you don’t have issue, Dec corrections may have been only in one direction. When PHD sends a command to reverse direction of Dec axis, then there may be big enough backlash for what you are seeing on PHD graph.

It’s not uncommon for mounts to have backlash in Dec axis especially in some high end mounts.



Is the mount the only to blame here? Could it be due to some software settings (EQMOD, PHD or SGP) that have to be tweaked? Does any of the software has a feature to mitigate stiction if it is culprit?



I used to have Celestron mount and it had huge Dec axis backlash and the best I could do was to increase PHD2 Max Dec Duration to as high as 2000msec and it worked quite well. Other settings didn’t seem to help.



I have done that but problem remains. Is it possible to tweak the backlash in EQMOD? There is a setting entitled, ‘Dec. Backlash’. This is currently set to zero.



I am not familiar with EQMOD. I believe you might get better responses in other forums dedicated to EQMOD or PHD2. I don’t think your issue is SGP’s problem.



I had the exact same problem that you have described. I am using an HEQ5 with EQMOD. I went through a lot of effort problem solving including checking out the mount from a mechanical perspective.

I posted on various forms and the major cause suggested was a power drop often caused by a low battery or a PS dropping when dew removers were cutting in. However, this was not my problem.

I fixed it by running a cable directly from the mount - bypassing my powered USB hub - and going directly to a new usb port in my laptop.

I can give more details if required but I would check your power first and if that isn’t the issue check your cables and and bypass any powered usb you may be using.


Many Thanks for your input Tim. I will consider your suggestion but my mount is directly connected to my laptop and through a dedicated 12V 5 AMPS power supply that is double regulated that is connected to an electrical source. However, I have been operating at high temperatures (25 Degree Celsius) 80 F where I have had issues with other similar PS in the past. They had thermal protection, so I experienced shut downs. A fix to this was to attach a PC fan to the back fins to cool off the unit. AS a precaution, I will attach another fan to the PS that feeds the mount.

I do not use powered cables as I employ all four USB ports directly from a laptop.

I found out that EQMOD has a Declination Backlash setting and preliminary analysis suggests that through this setting, the amount of declination slip could be reduced. Further trials will determine whether I could eliminate the backlash or not. I also discovered that a beta version of PHDII guiding has a backlash compensation but this is another possibility that could be used as a backup to this problem.

Many Thanks,