Fluke 5820A, Service Manual

Page: 116 / 158

5820A
Service Manual
5-8
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Figure 5-3. Porch
9. Adjust R175 so that a porch-waveform can be observed (refer to Figure 5-3).
10. Adjust the oscilloscope vertical setup to be 5 mV/Div.
11. Adjust R188 to make the bullet waveform shown in Figure 5-4. Its amplitude should
not be less than 7 mV.
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Figure 5-4. Bullet on the Porch
12. Adjust R175 to raise the porch level to the height at which fast edge is stable (refer
to figure 5-5).
13. Use a cursor on the scope to mark this porch level (Level I).
14. By adjusting R175, continue to raise the porch level to the height at which the fast
edge waveform is unstable.
15. Use a cursor on the scope to mark this porch level (Level II). A typical voltage
difference between Level I and Level II is 20 mV. (Refer to Figure 5-6).