Samsung RCD-2600 Service Manual page 21

3) FOCUS BIAS ADJUSTMENT
A. Turn power on without loading a disc.
__B. Set Oscilloscope Vol/Div to DC200mV.
C. Connect TP1 (Vref) to GND and TP3 (F.E) to positive terminal on the oscilloscope.
D. Adjust VR1703 so that the voltage is 200mV DC on the oscilloscope.
Negative port of oscilloscope FOCUS bias adjustment positive port of oscilloscope