I've had a CEM120EC2 for about 15 months. Until Saturday I used it with my refractors - WO71, TV127is, and AP155. Guiding has always been excellent and stars have always looked fine in the raw images. I've had a second system out in New Mexico for almost a year with a Planewave CDK12.5 on it accompanied by a QHY16200A camera. In the interim, I've been renovating an old observatory about 90 miles from my house. That observatory is finally finished enough that I could bring back the NM system and have both of my imaging platforms in one place.
The CEM!20EC2 has been in the renovated observatory for about 3 months now with my TV127is on it. I use a PierTech pier with it. The pad it sits on a 48" concrete cube (with rebar) with j-bolts connecting to a short rat cage arrangement using 3/4" in bolts and nuts. It's rock solid and is isolated from the rest of the observatory by a 1" border of packed earth. I spent the late afternoon on Saturday setting it up the PW system on the pier. Since I was switching computers at the same time there was quite a bit of wiring and software that needed to be upgraded/changed. By about 9PM I was ready to go. Between 9 PM and 11PM I found a few more user errors (loose screw in my OAG) and cleared those up.
At that point I was confident that I was finished with the teething issues. I proved this by guiding for 15 minutes each with two different guiding programs. I calibrated each one at the meridian and slewed to an object. Results were perfect - .2 and .3 arc seconds of RMS using the SKYX. and with MaximDL again got well under .5 seconds RMS in both axes. So, then I ran a 5 minute guided exposure. Every single star was elongated across the QHY16200A frame. I ran CCD Inspector and it reported that the collimation is essentially perfect and there is very little tilt. I then ran a short unguided exposure and I got the same egg shaped stars. The short exposure results meant that I could rule out an unstable pier. The CCDI results meant that I could rule out the camera or the optics. I was left with (a complete surprise) a mount problem. I then rotated the camera 90 and the elongation rotated with it At both angles the elongation was precisely parallel to the RA axis. I then ran a bunch of guided/unguided exposure. They all showed exactly the same defect with the stars and it didn't increase with exposure time.
I've fruitlessly exchanged emails and phone calls with iOptron over the past two days. They are unwilling to stipulate whether this is a problem with every one of these mounts or just for some of them (mine is one of the first). They have offered no useful advice to allow me to fix it myself. They are unwilling to take it back and fix it themselves or to give me a refund. So, I'm hoping that someone had this issue and somehow solved it.
I'd like to hear from anyone who owns any CEM120 mount with or without encoders about whether they have the same problem or not. I'd like to ascertain if this is inherent in the design or (sigh) user error.