Service manual

7.3.8 PTL (Pre-transfer Lamp)
When the belt transfer charge unit switches on, the transfer belt receives a
positive charge. Because the drum has a negative charge, the belt will be
attracted to the drum.
However, when there is toner on the transfer belt. This attraction is greatly
reduced. There is no toner on the transfer belt before the first color transfers
to the belt. However, there is toner on the transfer belt (before the second,
third, and last colors transfer to the belt), and in this case the attraction
between the drum and the belt is reduced. Hence, the difference in attraction
is most noticeable between the first and second color transfers. For later
color transfers, the attraction does not change so much, because there is
already toner on the belt.
The difference in strength of attraction of the belt to the drum between the
different color cycles means that color images may not be synchronized
correctly on the belt, as the position of the belt changes.
To counteract this problem, the PTL [A] exposes the drum to reduce the
potential of the white areas of the image before the first color toner is
transferred to the belt (it does not switch on for later toner transfers). The
reduction of the negative drum potential reduces the attraction between belt
and drum to the same level as if there was toner on the belt. This means
that the synchronization of color toner images on the belt will be better.
The PTL is especially effective for images that have a high proportion of
white areas, where the attraction between drum and belt will be great.
[A]
Detailed
Section
Descriptions
TRANSFER BELT UNIT
SM 2-107 A166/A187/A189
CÓPIA NÃO CONTROLADA
CÓPIA NÃO CONTROLADA