Brother HL-2700CN Series, Service Manual

Page: 91 / 377

IV-38
TS: To maintain the set point (temperature) for fusing of toner to
be approx. 160 ° C as appropriate by turning on/off the thyristor.
TA:
Reference temperature (approx. 185 ° C) to identify that it is
excessively hot inside the fusing unit. When it reaches to this
point, the relay RY turns off, the power supply to the heat lamp
is shut down, and the printer stops the operation.
TPS: Limit temperature to have the thermal cut-off start melting and
shutting down the power supply to the heat lamp if the
temperature control circuit should break down.
< Temperature Control and Safety >
The detection of the fusing temperature is performed by the thermistor and
transmitted to the temperature control circuit. The temperature control circuit
makes the comparative control with the basic control temperature signal and
ON/OFF control over the triac (FLS) so that the temperature of the heat roller will
be the preset temperature (PS). The temperature control is made in terms of the
both hardware and software, and detects any error with the following detection
meanings. Upon the detection of such error, the printer stops and the error
message is displayed on the operator panel.
H0: If the wire-cut occurred in the temperature sensor thermistor
(TH) or the breakdown such as wire-cut occurred in the circuit,
the wire-cut detection signal (THERR) is outputted. This signal
works to turn off the relay (RY-1) and the triac (FLS) and
subsequently stops the printer.
H1: If the surface temperature of the heat roller continues to be
higher than the preset value of abnormal temperature (TA) for
more than the specified time, CPU forces the HON signal and
ACOFF signal to turn off according to the timer control so that
the printer stops.
H2: If the surface temperature of the heat roller does not reach to
the preset temperature (TS) in the specified time after power-
on, CPU forces the HON signal and ACOFF signal to turn off
according to the timer control so that the printer stops.
H3: If the surface temperature of the heat roller continues to be
lower than the preset temperature (TS) for more than the
specified time, CPU forces the HON signal and ACOFF signal
to turn off according to the timer control so that the printer
stops.
H4: If the surface temperature of the heat roller continues to be
higher than the preset temperature (TS) for more than the
specified time, CPU forces the HON signal and ACOFF signal
to turn off according to the timer control so that the printer
stops.
HA: If the temperature of the heat roller becomes abnormal due to
the break-down of the control circuit etc., the temperature
detection circuit (CM2) transmits the ACOFF signal. This
signal turns off the relay (RY-1), and simultaneously makes
the CPU stop the printer.