Built-In Safety Measures; Overcurrent Protection; Lightning Protection - Canon LASER CLASS 3175 Service Manual

LASER CLASS 3170/3175/3175MS Chapter 1: Safety and Precautions

4.3 Built-in Safety Measures

4.3.1 Overcurrent protection

This fax is provided with an overcurrent protection circuit with built-in current
fuse and thermal fuse, to prevent abnormal rises in temperature if an
overcurrent flows to the motors and power supply due to driver IC trouble,
software lockup and short circuits.
Protected Parts
Document read motor
Stamp unit (option)
Power supply unit
Fixing heater

4.3.2 Lightning protection

This fax is provided with a function for protecting electronic components from
abnormal voltage caused by lightning.
Protected Parts
NCU board ass'y
Power supply unit
When protection is not possible
The NCU board sometimes may not be protected even by the
protection circuits if lightning strikes the telephone line.
NOTE
Safety Measures
IC protector (FU2) on SCNT board
Current fuse (FU1) on SCNT board
Glass-tube current fuse (F1 (125V, 15A), F2
(125V, 6.3A)), overcurrent protection circuit
Thermal fuse (446°F/230°C), thermistor
Safety Measures
Arrestors (AR1, AR2) located at the primary
side of the NCU board discharge a voltage of
more than DC 500±75V via the power cord.
Surge-absorber (NR1) located at the primary
side of the power supply unit goes into short-
mode at a voltage of more than 195V, and
breaks. After this, the glass-tube current
fuse F2 or F1 blows.
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