I have an AP900 that I have had for 15 years. It has worked flawlessly. A couple weeks ago I noticed what I thought was a minor DEC backlash issue, so printed out the instructions and went to work. I could barely detect any movement in DEC with the mount in Park Position 3, but figured I would go through the process. I verified that the set screw was properly tightened and followed the instructions to 'rock' the dec motor into place. I could not feel any backlash and figured things were going to be back to normal. I apparently made it worse...
This image shows what I now see in PhD 2. At some point it starts
making a dec correction and things keep getting worse, almost like
the corrections were moving in the wrong direction. I re-did
calibration in PhD multiple times to make sure I had not messed
anything up. In the PhD graph, each large vertical division is 25
points at 6 seconds per point, or about 150 seconds. The telescope
is a Celestron Edge HD 8". The guide camera is off axis and is a
ZWO ASI 290.
I changed the min move in dec to 5 to effectively disable dec
corrections right after this happened. You can see that the polar
alignment is fine, as there were no longer dec corrections. Up
until I tried to make the mount better, I was getting rms guide
errors consistently < 0.5", typically around 0.4". I have never
seen anything like this.
I ran the PhD guiding assistant and it verified that my polar alignment was not too bad, but that there was some serious backlash
This is verified by the backlash graph
I ran this test a year ago, and the backlash graph was a perfect
triangle. Clearly I am not doing the adjustment optimally. Do I
just need to fiddle with it to get it right? When I try to move
the dec axis I can barely feel any movement, am I going for no
movement at all?
When I 'rock' the motor into place, I place firm pressure on it
while I adjust the bolts per the instructions. I could certainly
use more force (or a rubber mallet), but not really sure if that
is the way to go.
Any advice would be greatly appreciated.
- Tom C