Based on the Bill of Materials in the service manual, here are parts you should stock if you repair mixers frequently:
The manual shows that the main L/R signal goes from the summing amp (IC14) → Main fader → Balance amp (IC15) → XLR drivers. Headphones are tapped before the main XLR driver. behringer xenyx qx1202usb service manual
Understanding the operational limits is critical for diagnostics. Based on the Bill of Materials in the