DEC guiding issue

[S Am]

I am experiencing unusual behavior with my mount.

Sometimes, PHD2 sends a series of pulses to the mount without being able to reduce the star-to-mount error for a certain period of time. Then, suddenly, the mount returns to the correct position.

This can happen at any time, with pulses in either the north or south direction, both before and after the meridian flip.

Sometimes there are no occurrences during an entire 6-hour session, but more often I experience between 10 and 20 occurrences per session.

Here is what I have done before posting this message:

• Read and understood the PHD2 documentation.

• Read the PHD2 Best Practices Guide.

• Watched all the videos in the Getting Help section.

• Tested several different balancing configurations for the Newtonian telescope on the mount.

• Tested different cable configurations to make sure that nothing is interfering with the mount's movement.

• Tested different settings, both with and without backlash compensation.

• Ran several automatic calibration sessions.

• Tested different levels of polar alignment accuracy.

Log link when everything works normally 2026-08-06

Log link showing the problem 2026-08-07

https://openphdguiding.org/logs/dl/PHD2_logs_uWGp.zip

At this point, I am out of ideas and I don't know what else I can test or investigate.

Any help or suggestions would be greatly appreciated. Thank you in advance.

Stephane

[Brian Valente]

Hi Stephane

This issue is mechanical in nature. The guide star moves away in Dec, and despite repeated attempts by PHD to correct it, continues for some time. Then suddenly it snaps back. 

This can either be stiction in the axis or something interfering with dec axis movement (such as a cable snag, internal cabling, etc.). I tend to think the latter, since it happens only occasionally. 

Notwithstanding your note about testing cable configurations, this seems like the likely cause.  You should move the mount to the location where the issue occurs and investigate further.

Brian

 

--
You received this message because you are subscribed to the Google Groups "Open PHD Guiding" group.
To unsubscribe from this group and stop receiving emails from it, send an email to open-phd-guidi...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/fd5b3f3c-6f49-497c-9807-fba871c8ae27n%40googlegroups.com.

--

Brian 

Brian Valente

astronomy portfolio https://www.astrobin.com/users/bvalente/ 

[S Am]

Thank you very much Brian for your quick response. I’ll keep investigating the cabling.

Just to understand, why doesn’t PHD2 increase the pulse duration if the mount doesn’t respond?

Stephane

It does - you can see it below. The guidepulse is equivalent to the offset measured: as it goes up, the guide pulse increases. If the offset measures the same amount as prior, it will receive the same guidepulse. Guiding does not know anything about the source of the issue, it simply measures the offset and provides the amount of correction needed to bring it back to zero.