HP LaserJet Enterprise 600 Service Manual - Page 54

Laser failure detection, Laser failure, BD failure, Scanner motor start-up failure

Page 54 highlights

The modulated laser beams generate the latent electrostatic image on the photosensitive drum according to the image data signals that the DC controller PCA sends. 1. As it receives a print command from the formatter, the dc controller outputs the SCANNER MOTOR SPEED CONTROL signal (/ACC) and rotates the scanner motor in order to rotate the sixsided mirror. 2. As the scanner motor starts rotating, the dc controller uses a LASER CONTROL signal (CNT0, CNT1, CNT2) to receive the /BD INPUT signal (/BDI) and force the laser to emit light . The dc controller detects the rotational speed of the scanner motor based on the timing the /BD1 signal is input and controls the speed to keep it constant. 3. While the scanner motor rotates at a constant speed, the dc controller passes the VIDEO signals from the formatter on to the laser driver PCA. The laser driver PCA emits light from the two laser diodes according to these signals: VDO1, /VDO1, VDO2, /VDO2. 4. The two laser beams pass through the collimator lens and cylindrical lens and strike the six-sided mirror that is rotating at a constant speed. 5. The laser beams, that are reflected off of the six-sided mirror pass through the focus lens and reflective mirror and focus on the photosensitive drum. The laser beams scan the drum surface at a constant speed. 6. As the six-sided mirror rotates and the laser beam scans the drum surface at a constant speed, a latent image forms on the drum surface. Laser failure detection The DC controller determines a laser/scanner unit failure and notifies the formatter, if the laser/scanner unit encounters the following conditions: ● Laser failure: The laser intensity is not detected for a specified value when the laser is turned on for a specified period during the scanner unit start-up period. ● BD failure: The BD interval is out of a specified value during a print operation. ● Scanner motor start-up failure: The scanner motor does not reach a specified rotation within a specified period from when the scanner motor starts rotation. 30 Chapter 1 Theory of operation ENWW

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The modulated laser beams generate the latent electrostatic image on the photosensitive drum
according to the image data signals that the DC controller PCA sends.
1.
As it receives a print command from the formatter, the dc controller outputs the SCANNER
MOTOR SPEED CONTROL signal (/ACC) and rotates the scanner motor in order to rotate the six-
sided mirror.
2.
As the scanner motor starts rotating, the dc controller uses a LASER CONTROL signal (CNT0,
CNT1, CNT2) to receive the /BD INPUT signal (/BDI) and force the laser to emit light . The dc
controller detects the rotational speed of the scanner motor based on the timing the /BD1 signal is
input and controls the speed to keep it constant.
3.
While the scanner motor rotates at a constant speed, the dc controller passes the VIDEO signals
from the formatter on to the laser driver PCA. The laser driver PCA emits light from the two laser
diodes according to these signals: VDO1, /VDO1, VDO2, /VDO2.
4.
The two laser beams pass through the collimator lens and cylindrical lens and strike the six-sided
mirror that is rotating at a constant speed.
5.
The laser beams, that are reflected off of the six-sided mirror pass through the focus lens and
reflective mirror and focus on the photosensitive drum. The laser beams scan the drum surface at a
constant speed.
6.
As the six-sided mirror rotates and the laser beam scans the drum surface at a constant speed, a
latent image forms on the drum surface.
Laser failure detection
The DC controller determines a laser/scanner unit failure and notifies the formatter, if the laser/scanner
unit encounters the following conditions:
Laser failure
: The laser intensity is not detected for a specified value when the laser is turned on
for a specified period during the scanner unit start-up period.
BD failure
: The BD interval is out of a specified value during a print operation.
Scanner motor start-up failure
: The scanner motor does not reach a specified rotation within
a specified period from when the scanner motor starts rotation.
30
Chapter 1
Theory of operation
ENWW