PHD2 Settings Sky-Watcher Star Adventurer GTi · DarthKul · ... · 10 · 243 · 0

Mike Dobres:
I had a similar very high backlash when I first received my GTi. To fix it I spent some time physically adjusting the DEC and RA backlash screws (instead of playing with the PHD2 settings).   The hole to adjust the RA backlash is under the patent number sticker. You'll need a small hex wrench to adjust it. The adjustment screw for the Dec backlash is a bit more difficult to access. You need to remove the cover just above the counterweight bar threaded hole. There are six round-headed hex screws holding it in place. Once you have removed the cover you will see the Dec adjustment screw. I adjusted this to move the worm gear closer to the main gear, thereby decreasing the backlash. Doing this reduced my backlash from about 6000 to 200, as measured by the Guiding Assistant in PHD2, with total RMS down to 0.4 while guiding.  While I was at it, I also redistributed some of the excess grease to make sure all gears and cogs were well lubricated.  Be careful not to tighten the Dec screw too much - I did this on the first try, and I had sudden spikes due to binding of the gears. I loosened the screw  a quarter turn and  all was well.  Take a look at this video. He removes the cover at 8:50 mins and points to the Dec adjustment screw.  https://youtu.be/Ym1_k3aJIkI?feature=shared

Mike Dobres:
I had a similar very high backlash when I first received my GTi. To fix it I spent some time physically adjusting the DEC and RA backlash screws (instead of playing with the PHD2 settings).   The hole to adjust the RA backlash is under the patent number sticker. You'll need a small hex wrench to adjust it. The adjustment screw for the Dec backlash is a bit more difficult to access. You need to remove the cover just above the counterweight bar threaded hole. There are six round-headed hex screws holding it in place. Once you have removed the cover you will see the Dec adjustment screw. I adjusted this to move the worm gear closer to the main gear, thereby decreasing the backlash. Doing this reduced my backlash from about 6000 to 200, as measured by the Guiding Assistant in PHD2, with total RMS down to 0.4 while guiding.  While I was at it, I also redistributed some of the excess grease to make sure all gears and cogs were well lubricated.  Be careful not to tighten the Dec screw too much - I did this on the first try, and I had sudden spikes due to binding of the gears. I loosened the screw  a quarter turn and  all was well.  Take a look at this video. He removes the cover at 8:50 mins and points to the Dec adjustment screw.  https://youtu.be/Ym1_k3aJIkI?feature=shared

100% agree with Mike. My copy came from factory with a significant backlash both in RA and Dec, and after adjusting, it was improving.

Another point: initially I was  driving it EQMOD, and I could never set it properly (it is not on the supported devices). I switched to GSS (that supports it) and it improved dramatically. I am not using Asiair.

Mike Dobres:
I had a similar very high backlash when I first received my GTi. To fix it I spent some time physically adjusting the DEC and RA backlash screws (instead of playing with the PHD2 settings).   The hole to adjust the RA backlash is under the patent number sticker. You'll need a small hex wrench to adjust it. The adjustment screw for the Dec backlash is a bit more difficult to access. You need to remove the cover just above the counterweight bar threaded hole. There are six round-headed hex screws holding it in place. Once you have removed the cover you will see the Dec adjustment screw. I adjusted this to move the worm gear closer to the main gear, thereby decreasing the backlash. Doing this reduced my backlash from about 6000 to 200, as measured by the Guiding Assistant in PHD2, with total RMS down to 0.4 while guiding.  While I was at it, I also redistributed some of the excess grease to make sure all gears and cogs were well lubricated.  Be careful not to tighten the Dec screw too much - I did this on the first try, and I had sudden spikes due to binding of the gears. I loosened the screw  a quarter turn and  all was well.  Take a look at this video. He removes the cover at 8:50 mins and points to the Dec adjustment screw.  https://youtu.be/Ym1_k3aJIkI?feature=shared

100% agree with Mike. My copy came from factory with a significant backlash both in RA and Dec, and after adjusting, it was improving.

Another point: initially I was  driving it EQMOD, and I could never set it properly (it is not on the supported devices). I switched to GSS (that supports it) and it improved dramatically. I am not using Asiair.

I tried to use GSS, for some reason after a short period of time it crashed. Did you have any issues with GSS?

Nope - GSS has been working reliably since nearly 2 years. Might happen that for some reason your installation got corrupted, I would try and reinstall it. Be careful that GSS has a different go-to behaviour across the meridian compared to EQMOD, that might appear as a bug, but is not. GSS is by design avoiding the flip across the meridian of a certain customizable angle.

Mike Dobres:
I had a similar very high backlash when I first received my GTi. To fix it I spent some time physically adjusting the DEC and RA backlash screws (instead of playing with the PHD2 settings).   The hole to adjust the RA backlash is under the patent number sticker. You'll need a small hex wrench to adjust it. The adjustment screw for the Dec backlash is a bit more difficult to access. You need to remove the cover just above the counterweight bar threaded hole. There are six round-headed hex screws holding it in place. Once you have removed the cover you will see the Dec adjustment screw. I adjusted this to move the worm gear closer to the main gear, thereby decreasing the backlash. Doing this reduced my backlash from about 6000 to 200, as measured by the Guiding Assistant in PHD2, with total RMS down to 0.4 while guiding.  While I was at it, I also redistributed some of the excess grease to make sure all gears and cogs were well lubricated.  Be careful not to tighten the Dec screw too much - I did this on the first try, and I had sudden spikes due to binding of the gears. I loosened the screw  a quarter turn and  all was well.  Take a look at this video. He removes the cover at 8:50 mins and points to the Dec adjustment screw.  https://youtu.be/Ym1_k3aJIkI?feature=shared

100% agree with Mike. My copy came from factory with a significant backlash both in RA and Dec, and after adjusting, it was improving.

Another point: initially I was  driving it EQMOD, and I could never set it properly (it is not on the supported devices). I switched to GSS (that supports it) and it improved dramatically. I am not using Asiair.

I tried to use GSS, for some reason after a short period of time it crashed. Did you have any issues with GSS?

Nope - GSS has been working reliably since nearly 2 years. Might happen that for some reason your installation got corrupted, I would try and reinstall it. Be careful that GSS has a different go-to behaviour across the meridian compared to EQMOD, that might appear as a bug, but is not. GSS is by design avoiding the flip across the meridian of a certain customizable angle.

Are you using the default configuration in GSS or made some changes? For example, sidereal rate, etc.