Sharp FO IS125N - B/W Laser - All-in-One Service Manual page 104

FO-IS125N
2.2.3 Hardware controlled protection function
Device Protective action
Heater lamp (fusing 1 The heater lamp is
device) forcibly turned off
when the temperature
of the fusing device
(thermistor value)
exceeds the upper
limit.
Laser (LSU) 1 When the cover is
open, the power sup-
ply to the laser system
circuits is shut off.
3 The sampling of S/H
signal is disabled
unless the VIDEO sig-
nal is active (laser on).
A fuse is installed in the following power supply lines: Optical unit (LSU) laser, Main motor, Pickup motor
Circuit description
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.
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.
Equipped with a circuit for
enabling output of the S/H signal
when the VIDEO signal is
received.
5 – 13
Purpose
Avoiding the abnormally The protection is activated
high temperature of the when F/W is out of control, the
fusing device. 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.
Avoiding the exposure to Malfunction due to the digital
laser beam. system circuit failure.
Avoiding abnormally high When F/W under develop-
output of the laser. ment is defective or runs out
of control, the protection is
activated. Normally, each sig-
nal is controlled following the
sequence by F/W.
Status to be activated