Output voltage ripple measurement should be taken directly across the output capacitor C21 or C22. Care has to be taken to minimize the loop area between the scope probe tip and the ground lead in order to minimize noise in the measurement. This can be achieved by removing the spring tip of the probe and ground lead and then wire a bare wire around the scope probe shaft. The bare wire should be in contact with the probe shaft because this is the “new” ground lead for the probe. The measurement can be taken by connecting the bare wire onto the ground side of the capacitor and the probe tip onto the other side of the capacitor. Figure 3-3 shows a diagram of this measurement technique.

Figure 3-3 Output Voltage Ripple Measurement Setup