Tektronix P6248, Service Manual

Page: 37 / 58

Adjustment Procedures
P6248 1.7 GHz Differential Probe Service Manual
25
8. Change the probe to
÷
10 attenuation.
9. Adjust the
÷
10 DC CMRR for minimum amplitude in the flat portions of the
displayed waveform. This adjustment does not affect the leading edge
transitions.
10. Keep the connections for the next procedure.
AC CMRR
1. Change the function generator to sine wave.
2.
Set the frequency of the function generator to 5 MHz and the output
amplitude to approximately 10 V pk-pk, (5 V peak).
3. Set the probe to
÷
1 attenuation.
4.
Change the oscilloscope horizontal 100ns/div. If necessary, adjust the
channel 2 volts/div and trigger level for a stable trigger.
5. The displayed sine wave is the common mode feedthrough. If the probe is
severely misadjusted, the waveform may be off screen.
6. Adjust the
÷
1 AC CMRR for minimum amplitude. Usually it is not possible
to completely eliminate the high frequency feedthrough.
7.
Change the probe to
÷
10 attenuation.
8. Adjust the
÷
10 AC CMRR for minimum amplitude.
9. There is some interaction between the DC and AC CMRR adjustments.
Repeat the DC CMRR adjustment steps 5 through 12.
10.
Remove all connections from the probe. Carefully replace the top cover of
the control box and the four retaining screws.
This completes the adjustment procedures.