Skywatcher EQ8 declination backlash adjustment

On Saturday because I had my Skywatcher EQ8 telescope mount polar alignment sorted, I decided I had to check and adjust the backlash in declination before mounting my Orion VX12 12″ Newtonian onto it. There were somethings I had experienced during polar aligning the mount which led me to believe that there were some issues which needed to resolve.

Now during the slewing when polar aligning with PHD2 the other night, I had noticed the red power LED was blinking at times. This is only supposed to occur when there is insufficient power getting to the mount. This is unlikely to be due to my 12V power source which is a DC adapter which supplies 4 Amp of current. This got me thinking whether there was something else causing it.

So what I did was to download the pdf file for the Orion HDX110 mount on how to adjust backlash, as it is essentially the same mount as the EQ8. File here: Adjusting the Declination Axis Backlash – Orion

I followed the instructions from the pdf and slewed about to find out what the backlash was like and whether any adjustments were needed for my mount. I noted that there was a point when the mount was pointing towards the 2 o’clock position where there was no backlash – clearly the mesh at that point was too tight.

Position where there was no declination backlash on my mount (2 o'clock position)
Position where there was no declination backlash on my mount (2 o’clock position) – shown here with my telescope but it was not mounted when I did the backlash adjustment

Now to start the adjustments, I had to remove the declination motor cover which is held in place by 2 x Philips screws and 1 x 2mm Allen screw. I have not included a picture of this with the cover off, as it is all in the pdf. But there are 2 x 3mm Allen screws holding the declination motor in place which need to be loosened by 1/4 to 1/2 turn before making any adjustments to the mesh.

Declination motor cover: 2 Philips screws and one 2mm Allen screw to remove to reveal the motor
Declination motor cover: 2 Philips screws and one 2mm Allen screw to remove to reveal the motor

The next step was to loosen 4 x 4mm Allen screws by 1/4 to 1/2 a turn at the bottom of the worm gear housing, so there is some leeway for the mesh adjustment.

4 x 4mm Allen screws to loosen by 1/4 to 1/2 turn before adjusting the mesh
4 x 4mm Allen screws to loosen by 1/4 to 1/2 turn before adjusting the mesh

The EQ8 mount has three 4mm Allen screws on the top of the worm gear housing hiding the actual mesh adjustment screws. Hence I had to remove these before I could make adjustments. The hidden screws are 4mm Allen screws on either side, whereas the center one is 2.5mm. They are fairly deep and need fairly long Allen keys to make the adjustments.

The three 4mm Allen screws hiding the 3 Allen screws which are used for adjusting the mesh
The three 4mm Allen screws hiding the 3 Allen screws which are used for adjusting the mesh

So I used the instructions from the pdf to loosen the mesh i.e. increase the backlash. The procedure to do this involves loosening the two outer screws before tightening the center screw. This resulted in too much backlash all throughout the full 360 degree range. But this also meant I could re-tighten this again to get the backlash better.

Now the important point to note (which is not pointed out in the pdf), which I found during the adjustment, is that if the mesh is tightest towards one side when the clamp is pointing at an angle rather than straight up or straight down i.e. the least backlash is not either at the top or bottom, then it suggests that one of the side screws is looser than the other. This means that the adjustment of the side screws needs to be made differently.

I noticed in my setup when tightening up the mesh that the screw to our right (of the three) was much looser than the one on the left and could be adjusted in (clockwise) more. And when I rechecked the backlash, this was now much less all round and with no point where the mesh was too tight.

On reflection, this is what I think has happened:

  1. My mount declination mesh was too loose on the west side and too tight on the east side of the mount, which correlates with the fact my mount had no backlash at the 2 o’clock position i.e pointing to the east.
  2. By adjusting the declination backlash, I no longer see the blinking of the red power LED, which suggests that there is no binding of the gear which previously was probably resulting in the mount computer thinking that there is insufficient power getting to it.
My Orion VX12 mounted on my EQ8
My Orion VX12 mounted on my EQ8

And now that the backlash is adjusted properly, I have mounted my Orion 12″ Newtonian onto it. Now with the full load, I am not seeing any blinking of the power LED when slewing about. This tells me that the mesh is not too tight. And I note that the mount is coping very easily with moving this telescope about, as if with great ease.

The next step for me is to get a base plate to mount to the top of the tube rings, so I can mount my Skywatcher ED80 on the top to act as the guide scope. And then I can work on getting the periodic error curve created ( to see what the native periodic error of this mount is), refine the curve and then to apply the periodic error correction in EQASCOM. Exciting times ahead.

Boon