I was testing my brand-new iOptron CEM40EC during the last few nights.
Due to the rattling of RA axis (which is well described here on CN and on other forums) I have installed the new beta firmware upgrade from iOptron and this issues was reduced almost completely, so the RMS values of both RA and Dec axes are now simillar and pretty low (less than 0,4 arces with full Moon and poor seeing).
But, analyzing the guide logs, I noticed that other issue existed even before the firmware upgrade and that it continues after the upgrade: unexpected and intermittent large spikes of the RA axis.
Namely, RA axis made occasional spikes spending from 20 to more than 60 pixels. It is completely random, and as you can see from the attached logs, it happened once during one longer guiding session (more than 1 hour), but sometimes few such spikes happened during just 5 minutes of guiding.
It is happening using classic laptop-based PHD2 guiding and with ZWO’s AsiAir (also PhD2-based) control of the mount, so it is not related to the guiding software. I have also changed the USB cable with a new high-quality golden-plated contacts USB cable and it happened again.
It is very important that the guiding improved with new firmware, but those RA spikes were present in the guiding logs using the original firmware (190422), too, so it is unrelated tot he firmware upgrade. It is some electronic malfunction or other serious issue?
Last session, the RA spikes didn’t happened at all during more than an hour and although the RMS values were low (under 0.4 arc-sec) for both RA and Dec axes, the two guiding curves were completely separated: RA curve never reach zero baseline.
I am attaching a guide-log from the last night and a screenshot of PHD2 showing an isolated RA spike.
Since I am very upset with this issue, I will appreciate your opinions and suggestions.
Let me say that, apart from that issue, I am very satisfied with the new CEM40EC.