DEC calibration issue with OAG guiding

[Cimitar]

Evening folks,

I'm having a bit of trouble with a DEC guiding issue on my Meade LX200 ACF 8" when using an OAG.
For the past couple of years I've been successfully using an Orion SSAG and guidescope. This has worked well, however, I thought I'd make the move to OAG due to my longer focal length and SCT.

My specific problem is I can't seem to get PHD to calibrate because it won't move the mount sufficiently in DEC axis. RA movement appears to be fine.
PHD calculates the calibration step at 200. This number appears to be fine for RA because it completes that part, however, when it attempts to move North/South the star barely moves. I'm using an Orion TOAG and ZWO ASI174MM. Everything is focused properly and the balance is good. I tried clearing the backlash, adjusting the guide rate setting etc. sadly to no avail.

When I switch back to the guide scope, the mount is fine and PHD happily guides in RA/DEC.
This makes me think it's a user issue with the software. Perhaps I'm missing a specific setting somewhere in PHD?

Cheers, Evan

[Cimitar]

I had another look at PHD and the calculated calibration step size is set at 200. I manually increased this to 500 (as a guess) and the mount successfully moved North/South.
The calibration succeeded, however, what I'm not sure of is why the mount can readily move in RA (with a step size of 200) but not in DEC?
My first thought is backlash in the DEC axis, but then why wouldn't this affect the guide scope?

[Cimitar]

Just wanted to share the solution to my 8" Meade LX200 DEC guiding issues with the OAG, in case it's useful to someone else in the future:

1. The scope was ever so slightly out of balance in DEC, with a tendency for the corrector plate to drift to the South. I corrected this, and made it so the scope (corrector plate end) was ever so slightly imbalanced towards the North.
2. I disabled all anti-backlash settings in the hand controller (RA & DEC). I did this by setting the percentages to 0%
3. I enabled the DEC backlash option in the PHD2 guide settings.
4. I still wasn't happy with the recommended 200 calibration step size, so I manually entered 400. This worked fine.

The mount happily moved in RA & DEC, and after a bit of fiddling with the guide settings I was able to achieve the attached guiding graph. Pretty happy with the star plot as well.
Still a bit of movement in RA that I need to sort out, however, I shot a 600sec ISO800 exposure on the Eagle Nebula (Canon 600D DSLR) and the stars look alright :)

The only thing I wasn't sure of was my Tot RMS error. It seems a tad high. However, I was using a guide scope previously and the RMS error there was always below 1.
I wonder if the image scale might have changed due to the OAG though? If it has, it might be distorting the figures? :question:

Cheers, Evan