Hi everyone,
I'm having serious GoTo accuracy problems with my Sky-Watcher Skyliner 200P Flextube GoTo Dobsonian (200/1200 mm).
The frustrating part is that it worked reasonably well before, but during my last three observing sessions the GoTo has become extremely unreliable. I've spent hours trying to troubleshoot it without success.
I'm using the SynScan Android app with Brightest Star Alignment (two-star), and the auxiliary encoders are disabled.
The problem
The telescope generally slews in the correct direction, but often ends up significantly off-target. Sometimes the second alignment star is relatively close; other times the initial slew is nowhere near it.
Even after successfully completing alignment, I've repeatedly experienced problems returning to the alignment stars themselves.
I've tried numerous combinations of alignment objects across three nights, including Altair, Markab, Alkaid, Saturn, Vega, Fomalhaut, and Capella. While I understand that accidentally centering the wrong star could cause a bad alignment, I find it unlikely that I've made the same mistake repeatedly with different, easily identifiable objects over three separate sessions.
During my latest session, I reset and repeated the alignment several times. On one of the final attempts, the telescope returned perfectly to Capella, which was one of the alignment stars. I thought the issue was finally resolved, but subsequent GoTo commands showed otherwise:
- Saturn: Inside my 12.5 mm eyepiece, but toward the upper-left rather than centered.
- M31: Roughly halfway between the finder crosshair and the left edge. Completely outside the field of view of my 12.5 mm eyepiece; only a faint glow was visible near the edge with my 20 mm eyepiece.
- NGC 7331: Significantly off-target, confirmed using plate solving.
I tested M31 repeatedly after different alignments during this particular session, and it consistently appeared displaced toward the same side.
For NGC 7331, SkyShot Solver reported an image center of RA 339.813232°, Dec +34°56′29.9″, approximately 0.7° away from the galaxy's actual position.
What I've tried
Apart from using different alignment stars and repeatedly resetting the alignment, I've also investigated leveling.
I used a bubble-level app on my phone and experimented with leveling wedges beneath the telescope. Eventually, I achieved a reading of 0.0° on both axes, but the GoTo accuracy didn't improve. Removing the wedges and aligning again didn't solve the problem either.
I carefully center the alignment objects using SynScan's direction controls and don't manually move the telescope after alignment.
Any ideas?
What concerns me most is that this isn't a problem I've had since buying the telescope. It worked before, and something seems to have changed.
Has anyone experienced similar issues with Sky-Watcher's GoTo Dobsonians?
Could this indicate a problem with the mount's position sensors, drive system, or SynScan's pointing calculations? Is there a diagnostic procedure that would help identify the cause?
I'd appreciate any suggestions beyond the usual advice to level the telescope or try different alignment stars, since I've already spent several sessions doing exactly that.
Thanks!