Re: Thanks to AP stuff
I sent a short video to support@... showing how my DEC motor badly works. I tried a new CP4 and it works a bit differently than CP3. Now, RA motor moves as expected, no problems with W-E buttons, no yellow light even if DEC motor is connected.
But when I press S or N button and even hold it, DEC motor starts moving in proper direction but only for 1-2 seconds, then stops and yellow light is seen, RA is still OK, can rotate around polar axis, but DEC works only for 1-2 sec. It is always repeatable this way.
So, you was right that probably DEC motor/encoder is bad. I do not know if only encoder should be replaced with a new one and/or also motor needs to be exchanged.