Electrical Adjustment - Canon LBP-1760 Service Manual

CHAPTER 4
B. Electrical Adjustment
1. Top margin adjustment
As VR501 on the engine controller PCB is adjusted at the factory, its adjustment at the time of
installation is not required.
However, when the engine controller PCB is replaced in the field, the top margin needs to be
re-adjusted. Also, if the top margin of test prints made after laser/scanner unit replacement is
not 2.0mm, this adjustment is necessary. The adjustment procedures are shown below.
1) After setting the VR501 to the center position (±0) on the engine controller PCB, set the paper
in the cassette. Press the test print switch to make several test prints.
2) Measure the length from the leading edge to the print pattern ("a" in Figure 4-7-4). Measure
all the test prints and calculate their average.
3) Adjust VR501 so that the calculated value in step 2) becomes 2.0mm.
The pattern image shifts in the "+" direction in Figure 4-7-4 if VR501 is turned clockwise,
and in the "-" direction, counterclockwise. Turning the VR501 one scale shifts the pattern
about 0.6mm.
For instance, if the average value calculated in step 2) is 1.4mm, the difference is 0.6mm.
Therefore, turn VR501 clockwise for one scale. (See Figure 4-7-5.)
4) Make several test prints again, and perform step 2). Check that the top margin is 2.0mm.
If the value is incorrect, repeat steps 1) to 4).
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Leading edge of print
Figure 4-7-4
–
a
+