CEM 120 (iOptron) stops in RA and whines when slewing

I dont know if its the same/related but eq6-r 's are notorious for this.
The cause in that case is too low of voltage supplied to the mount, made worse by poor balance. 


if you run off a battery, it may not perform as well in cold temperatures and the higher amp draw of a slew would result in more voltage drop. It may also simply be low on charge. If you have a set of multimeters, or the mount controller/software may have a voltage readout option, you might be able to check this. 

In my case with an eq6r, battery would supply +12.4v, but after voltage drop the mount would recieve 11.6v or less with the standard power cable. I use a 13.8v DC booster.


Just my 2c from experience.

I have had the same problem and this was due to to lose or to tight gears on the RA. Have you tried to losen the RA gear tension? Just a very slight bit should fix the problem. There is a video on youtube and some documents on the Ioptron site how to do this.

Sorry just before you do that …

Mine made a hideous sound when binding.  If yours is only "whining" or "whirring" then maybe yours is too loose which might suggest other issues ..c an you clarify if its just motor noise or hideous binding noise? 

If it was too loose, you would be able to move it by hand, so im assuming its more than "whining"?

When this happened to me, I found a loose cable inside of the cable management input panel (on the RA axis). It has a green plug that was loose and would disconnect slightly causing this sunroof your seeing. It only happened at certain angles but would otherwise track fine. 

I ended up having to tape the connector so that it wouldn't come loose. 

I'll see if I can dig up a picture. 

Jason

I also think it's a power issue. Make sure your power supply is outputting at least 12-13volts.

I have had this issue quiet a lot.
I first though it was a bad balanced as mentioned,  but this was not the case.
I then thought that it was poor mesh,  but this also didn't quiet fix the issue.
What it was was the USB 2.0 cable.
This may sound odd,  but i am running 5 meter cables and i went with a startech active extension cables.
Never had an issue since.
https://www.startech.com/en-au/cables/usb3sab5m
https://www.mwave.com.au/product/startech-5m-usb-20-active-extension-cable-mf-ab68977

I have CEM70 and got that worrying whine on one occasions - used in a lab to rotate a spectrometer, not outside for imaging. But had a similar issue.

It might be binding, but unlikely for such large worm/gears on the 70 and 120, as they are normally shipped with some slack to the point where there are often recommendations to tighten the motor and belt.

If you are plugged in or can see the power draw through software, or fully confident you are not low in voltage, then unlikely to be that.
Long cables could be issue, maybe not.

But, when the system needs to be rezeroed, you can get this problem. 

Never manually reset to zero whe you are in a failed slewed position different from the registered home position, as the software thinks it is pointing where it was and home position is way off - you end up running out of gear and its trying to turn when it cant. In that case, I unlock RA or DEC and manually move to see where the limits are and get back to roughly midway and ask the mount to find home automatically. You might already know this.

Another issue can be the software resets the location data, and where you are pointing is not where you think, slews are way off and so is the home position. End result is you bang into the end of the axis turn, hear the whine and need to refind home position. 

Not sure if this is useful, for me it was a case of reset of the GPS coordinates, for others it can be a manual move to home that gives an offset to the actual registered home position, and it runs out of rotation when you try to slew.

Zero damage done, stepper motors are astonishingly strong, but just eye ball the relevant RA or DEC belts just in case there is any thinned out regions that will give a periodic bump in guiding if so.

Ya, I gave up on the saddle power. Granted with two power inputs for both sides of the saddle give great options for power, but the USB was flaky and for my the iguider always disconnected. With a pegasus pb adv, every disconnection and mount connect failure disappeared immediately.

Pity you're zeroing doesn't work. It should though, avoids any mistakes with manual zero position not being central to the full slew east and West.  Did you Install the latest firmware? Upgrading is very simple now with the software tool, just on the off chance it might be useful.