I found the service manual for ECLER NUO 3 on this website, thank you!
The mixer has a sound defect with all 3 PHONO inputs, a range in the high-end of the spectrum is lost. Other inputs (non-PHONO) have no issues. When using PHONO, the issue exists on MASTER and REC out. There must be something wrong the PHONO tracks themselves but I am surprised that all 3 are affected.
Can someone provide hints on how to find the root cause ? And whether it's worth repairing.
Thanks a bunch