Cautions And Warnings - HP LaserJet II Serie Manual De Instrucciones

HP 33440/HP 33449 COMBINED SERVICE MANUAL
WRITING: Stage Three
After rotating past the conditioning station, the drum has a uniform –600 V potential on its
surface. At the writing station, a laser beam is used to discharge this potential in selected areas by
focusing laser fight on selected portions of the photoconductive drum. This creates what is known
as an electro~tic image. This image is later developed into a visible image,
The following is an explanation of how laser light is controlled to acMeve the electrostatic image
described above. Laser light is produced by a sm~ laser diode which is turned on and off by
suppling or denying power. The fixed focus beam of the laser diode is directed onto a six-faced
rotating polygon mirror (see Figure 5-7). As the mirror rotates, the beam reflected off the mirror
sweeps in an arcing fashion. Through a set of mirrors and lenses, the swept beam is brought
into focus to describe a horizonti line on the photosensitive drum. The beam reaches the drum
through an opening in the top of the EP-S Cartridge.
Because the beam is sweeping? the entire len@h of the drum can be covered by the beam;
similarly, because the drum is rotating, the entire circumference can be covered. This sweeping
of the drum and modulation of the beam allows exposure of dl desired surfaces on the drum (see
Figure 5-8). This is similar to how the electron beam in a television set scans to form a video
image on the screen.
The speed of the Scanner Motor (which rotates the polygonal mirror) and the speed of the main
motor (which rotites the drum) are synchronized so that each successive sweep of the beam is
offset on the surface of the drum by 1/300 of an inch. The beam can aso be turned on and off
at such a rate as to place an intermittent series of dots of light every 1/300 of an inch in the
horizonti direction. Thls is how the printer achieves its 300 x 300-doti-per-square-inch resolution.
(Note that one aspect of the HP 33449's Resolution EnhancementTM feature Wows for more
defined dot placement in the horizonti direction.) The Scanner Motor is controlled by the
SCNCONT line from the DC Controller. This voltage level varies depending on the Scanner Motor
speed feedback signals FG+ and FG– (see Figure 5-15 also).
Before the beam reaches the drum at the beginning of each sweep, it is reflected
off
a
smd mirror
into an optid fiber cable. This momenti~ pulse of fight is sent down the optid fiber to the DC
Controller PCA where it is converted to an electrid signal which, in turn, is used to synchronize
the output of data for one sweep (smn line). This pulse– ~led the Beam Detect pulse– is dso
used to diagnose problems with the laser or scanner motor. (See Figure 5-8.)
After passing the writing stition, the drum's surface has an invisible electrostatic latent image.
The portions of the d~m not exposed to the laser are still at the –600 V potential (placed
there by the Primary Corona) while those portions exposed to light have been discharged to
approximately – 100 V.
Note
Because the HP 33440 and ~ 33449 printers are class I laser products, they are
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safe for office or dati processing use. The laser used in the pfinter is a solid state,
&
b
infrared, class In laser.
warning
Although the infrared laser beam is invisible, eye damage may result if direct
or indirect (reflected) eye contact with the laser beam should occur. Heed all
CAUTIONS and WARNINGS when woking on the printer with covers removed or
with the laser unit itself.
5-8