Strange PHD Alert

[JohnSadlerAstro]

Hi,

I had the setup out in quite a strong breeze yesterday evening to try to find the cause of the RA motor failing to respond to PHD commands. Changing ST4 cable and reinstalling PHD seemed to sort out that  issue, but when I calibrated on Arcturus, this really weird message came up:

Can anyone explain what this problem is and how I can fix it?

Thanks for looking  

John

[Adreneline]

Hi.

I got the same thing exactly a few nights back. I am ashamed to say my immediate response was "for goodness sake!" (mega-frustration). I chose to ignore it and took the following 15x600s  Ha subs - despite possible poor guiding warning.

The focus might be a bit off but the guiding seems fine.

No sign of the same error on the following two nights so I have no idea what it means or why it happened but everything seems fine to me.

Sometimes it seems to tell me "it's broke" when in fact it just isn't, and I shouldn't try to fix it!

Sorry I can't be of any help.

[newbie alert]

It's best to calibrate at DEC 0 and on the meridian. 

[kens]

A guide log would be easier to review than a screen shot. But looking at your guide rates dec is showing as 9"/s which is 0.6x sidereal. That sounds like a plausible setting. The RA rate is 6.4"/s which , adjusted for declination, is 6.7"/s which is less likely to be a guide rate setting in your mount. So this is indicative that the issue is (possibly) on RA - possibly. Periodic error is a candidate

Other issues are a fairly high orthogonality error (7 deg) and signs of backlash issues on the dec axis (the white points at the end of the dec leg)

These problems can lead to inaccurate guiding as the calculated Ra and Dec corrections could be wrong. Wrong rate leads to wrong sized guide pulses. Orthogonality error leads to guide pulses applied in part to Dec rather than RA and vice versa.

 

 

[Pompey Monkey]

20 hours ago, newbie alert said:

It's best to calibrate at DEC 0 and on the meridian. 

Dec 0, or close to it, yes.

On the meridian? I'm not so sure - this is where the mount can exhibit the most slack/backlash in the RA axis as it "flops" over due to small imbalances. This is especially relevant for cheaper* mounts like the Skywatchers. The majority of my subs lost to star-trailing happen around the meridian, particularly if it's a bit breezy...

I find it best to do calibration either East or West of the meridian, on the same side of the flip where I'm imaging.

* cheaper is a relative description!