Sharp FO IS125N Service Manual - Page 104

Hardware controlled protection function, Device, Protective action, Circuit description, Purpose

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FO-IS125N 2.2.3 Hardware controlled protection function Device Heater lamp (fusing device) Laser (LSU) Protective action Circuit description Purpose 1 The heater lamp is The circuit forcibly turns off Avoiding the abnormally forcibly turned off (resets) the control signal of the high temperature of the when the temperature heater lamp when the thermistor fusing device. of the fusing device value reaches 238 ± 6 °C. To turn (thermistor value) on the heater lamp again, it is nec- exceeds the upper essary to reset all system or limit. power down once. In other words, once the protective action is per- formed, the protection is not can- celed automatically even if the temperature detected by the ther- mistor decreases. 1 When the cover is Equipped with a regulator circuit Avoiding the exposure to open, the power sup- for producing the laser system laser beam. ply to the laser system power (+5 V) supplied to the LSU circuits is shut off. from +24 V power supply inter- rupted by the interlock. 3 The sampling of S/H Equipped with a circuit for Avoiding abnormally high signal is disabled enabling output of the S/H signal output of the laser. unless the VIDEO sig- when the VIDEO signal is nal is active (laser on). received. Status to be activated The protection is activated when F/W is out of control, the microcomputer ADC is defective, or other abnormality occurred. Normally, the heater lamp is turned on/off by monitoring the temperature using F/W. Malfunction due to the digital system circuit failure. When F/W under development is defective or runs out of control, the protection is activated. Normally, each signal is controlled following the sequence by F/W. A fuse is installed in the following power supply lines: Optical unit (LSU) laser, Main motor, Pickup motor 5 - 13

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FO-IS125N
5 – 13
2.2.3 Hardware controlled protection function
A fuse is installed in the following power supply lines: Optical unit (LSU) laser, Main motor, Pickup motor
Device
Protective action
Circuit description
Purpose
Status to be activated
Heater lamp (fusing
device)
1
The heater lamp is
forcibly turned off
when the temperature
of the fusing device
(thermistor value)
exceeds the upper
limit.
The circuit forcibly turns off
(resets) the control signal of the
heater lamp when the thermistor
value reaches 238 ± 6
°
C. To turn
on the heater lamp again, it is nec-
essary to reset all system or
power down once. In other words,
once the protective action is per-
formed, the protection is not can-
celed automatically even if the
temperature detected by the ther-
mistor decreases.
Avoiding the abnormally
high temperature of the
fusing device.
The protection is activated
when F/W is out of control, the
microcomputer ADC is defec-
tive, or other abnormality
occurred. Normally, the heater
lamp is turned on/off by moni-
toring the temperature using
F/W.
Laser (LSU)
1
When the cover is
open, the power sup-
ply to the laser system
circuits is shut off.
Equipped with a regulator circuit
for producing the laser system
power (+5 V) supplied to the LSU
from +24 V power supply inter-
rupted by the interlock.
Avoiding the exposure to
laser beam.
Malfunction due to the digital
system circuit failure.
3
The sampling of S/H
signal is disabled
unless the VIDEO sig-
nal is active (laser on).
Equipped with a circuit for
enabling output of the S/H signal
when the VIDEO signal is
received.
Avoiding abnormally high
output of the laser.
When F/W under develop-
ment is defective or runs out
of control, the protection is
activated. Normally, each sig-
nal is controlled following the
sequence by F/W.