Fluke 5500A, Service Manual

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5500A
Service Manual
6-120
R57
R16
R1
R168
Ledge on center line
om041f.eps
Figure 6-35. Adjusting the Ledge with R16
Note
Aberration adjustments are interactive with rise time adjustments. When
you have completed this aberration adjustment, verify the edge rise time to
ensure that it remains within tolerance. If it does not, repeat the aberration
and rise time adjustments until you achieve the best compromise, within the
listed tolerance levels.
6-153. Adjusting the Edge Aberrations for Board 5500A-4004
Follow this procedure only if you have Board 5500A-4004 (Fluke PN 937383).
1. Adjust the dc offset on the 11801B so the peak of the square wave is on the center
line.
2. Change the time/div on the 11801B to 5 ns/div.
3. Adjust R16 so that the wave crosses the horizontal center line one division before the
vertical center.
4. Slowly adjust pot R57 and observe its effect on the first 15 ns of the waveform.
5. Adjust R57 so the rising edge falls back and crosses the horizontal center line one
division before the vertical center. The edge should cross the center line at two
points, where it rises and falls, and these points should be 20 ns apart. Refer to
Figure 6-36.
6. Change the time/div on the 11801B to 2 ns/div.
7. Now adjust pot R1, and observe the ledge that occurs within the first 2 ns of the
rising edge. Adjust R1 so this ledge is as flat as possible. Refer to Figure 6-37.
8. Now adjust R57 until this first ledge is on the horizontal center line. When you make
this adjustment, the ledge will lose some of its flatness.
9. Return to R1 and flatten the ledge as much as possible. Then return to R57 and try to
position the ledge on the center line while keeping it as flat as possible. You want to
achieve the best combination of flatness and position.
As you make these adjustments, make sure the peak remains between 4 ns and 6 ns.
It is possible to achieve a very flat ledge close to the horizontal center, but if the
peak is too high or too low, then the aberrations will not be properly adjusted.