Known Issues and Building tipps for yocto 808 Clone Batch2 - January 2014 pcb version
Noise section:
Measurement AC !!
Adjust the TM4 trimmer for 130mV on pin 1 of 4558.
its important to use a good DMM (multimeter), most cheap DMM have in AC voltage measurement with 3digits high failure rates and cant display 160mV - shows only 0,01.
i highly recommend a 4,5digits or better DMM with 0,1% tolerance
i have at least 250mV so changing R127 to 47K ...