Gestetner B147 Service Manual page 264

TROUBLESHOOTING GUIDE
Subject
Crow marks When making duplex prints in
low temperature and humidity
conditions, crow marks may
appear on black images,
especially in halftone areas
on the 2
Symptoms related to color
Faint image (black) Only black becomes lighter.
Magenta and/or cyan Magenta jitter may appear at
jitter 67 mm and/or cyan jitter at
165 mm from the trailing
edge.
SM
Symptom
A charge is applied to the paper at each
color station in order to attract each
toner onto the paper. Therefore, the
initial toner colors will receive multiple
charging as they pass each station,
nd
side. which increases the attractive force
between the toner and paper. Since
black is the last toner to be applied, the
attractive force between it and the paper
is lowest. Black toner moves on the
paper during transport to the fusing
section, due to discharge from the toner
to the surrounding guide plates.
The transfer belt position is not in the
correct position.
If the registration roller speed is too fast
for the paper types used, the shock
when the trailing edge has just passed
the registration roller generates
vibration, causing the jitter.
This may appear especially when using
thick paper because of its stiffness.
Cause
Using SP2-301 (Transfer Current), increase the
paper transfer current for black in the mode in
which the problem occurs.
NOTE: White dotted lines may appear on outputs
if the transfer current is increased too much.
Therefore, after adjusting the transfer current, it is
necessary to check the results by making a solid
or halftone image in duplex mode.
Check the transfer belt unit position and/or the
transfer belt unit release lever.
Adjust the registration roller speed depending on
the paper types and/or mode selected.
SP1-004-4: Normal paper (1200 dpi)
SP1-004-5: Normal paper (600 dpi)
SP1-005-3: Thick paper (1200 dpi)
If SP1-005-3 cannot improve the level even when
setting it to "-1.0", follow the procedure below.
1. Set SP1-005-3 to "-1.0".
2. Print the samples by adjusting SP1-004-4 from
100% (-0.2% to -0.8%).
After adjusting SP1-004-4, check the image
quality also with normal paper in the 1200 dpi
mode. Readjust it so that the image quality
level is acceptable for both thick and normal
paper if necessary.
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Action
B147/B149/B190