Adjusting The Ld Unit Channels - Gestetner B070 Service Manual

3.17.5 ADJUSTING THE LD UNIT CHANNELS

Small pitch banding could occur with this machine due to:
• Characteristics of the drum
• Variations that occur over time in the amount of light emitted by each channel
The quantity of light emitted from each channel of the LD unit is adjusted at the
factory. However, SP codes are provided so you can test and adjust the quantity of
light emitted from each channel. Patterns No.4~8 generated with SP2902 002
(Test Pattern – IPU Printing Test Pattern) allow you to visually compare channel
output, and SP2105 003~010 (LD Power Correction) allows you to do the
adjustments.
Test Patterns and Adjustment
Print the test pattern with SP2902 002, No.5.
The test pattern is a "caterpillar" pattern printed for every channel on one sheet for
A3 paper. The sample on the next page shows a test. Pattern 8 is a pattern for
each of the eight channels (0~7). Patterns 1~7 compare each pattern with Ch0.
In the sample pattern on the next page, note the darker appearance of Ch4 in both
Pattern 4 and Pattern 8, compared with the uniform appearance in the patterns for
the other channel. This indicates that Ch4 requires adjustment.
Light Quantity Adjustment
Adjust with SP2105 (LD Power Correction) 003 ~ 010. Then print the test pattern
again to check the effects of the new settings.
If a pattern is darker or lighter than the others, the quantity of light on that channel
should be reduced or increased.
While visually checking, Pattern 8 in the sample is sufficient to detect a difference
in the density of the patterns; the other patterns (1~7) allow more detailed
comparison with Ch0.
To perform adjustment for the channels, use SP2105 (LD Power Correction) 003 ~
010.
In the case of the sample print on the next page, we can see that Ch4 requires
correction because it is too dark; therefore, the value of SP2105 007 (the SP code
for Ch4 adjustment) must be lowered.
Generally, the amount of adjustment required can be determined by increasing or
decreasing the SP setting (in this case, reducing the setting for SP2105 007) and
then printing the text pattern again to confirm the results of the adjustment. The
adjustment should be done until the dark (or light) pattern matches the other
patterns.
SM
CÓPIA NÃO CONTROLADA
COPY IMAGE ADJUSTMENT: PRINTING/SCANNING
3-155
CÓPIA NÃO CONTROLADA
B070/B071