Canon LBP1760P, Service Manual

Page: 49 / 394

The printer does not supply power to the fixing heater in the STANDBY mode.
The CPU detects the temperature of thermistor based on the FSRTH signal when the /PRNT
signal is input and right before the main motor is driven. If it is below the specified tempera-
ture, at the same time as the main motor rotation reaches the specified speed, the CPU rises the
temperature to the specified value. The CPU sets the THERMISTOR SWITCHING signal
(/HITMP) to “H” to change the sensitivity of the thermistor.
The printer sets the /HITMP signal to “H” when the temperature of the fixing heater is low
(during warm-up) and to “L” when the temperature is high (normal temperature control), in
order to increase the detection precision of the FSRTH.
The CPU starts controlling the temperature of the fixing heater to achieve the specified print
temperature when the /TOP signal is output.
The target fixing temperature is set based on the following five conditions, and the tempera-
ture is controlled.
1. Initial temperature detected by the thermistor at the time of fixing unit warm-up
2. Print intervals (first print/intermittent print/continuous print)
3. Print paper size (A4, Letter, Legal/Other sizes)
4. Resolution (600DPI/1200DPI)
5. Print mode (See Note) (normal mode/rough paper mode/OHT mode/universal mode)
The print paper size, resolution and print modes have the correlations as shown in the table
below.
Table 2-2-1
When printing at 600DPI, target fixing temperature is higher compared to printing at 1200DPI
as the feed speed is doubled. When printing in the universal mode at 600DPI, the throughput
is decreased if more than the specified number of sheets are fed continuously. This prevents
elevation of temperature caused by feeding of small size paper at the edges of the fixing unit.
Note: There are four print modes: normal mode, rough paper mode, OHT mode, and universal
mode. The fuseability is improved when the rough paper mode uses Bond paper
(90g/m
2 ) and when the OHT mode uses OHT.
The engine controller judges the paper size based on the paper size information from the
paper size detection switches when paper is picked up from the cassette, and from the
video controller in case of multi-purpose tray pick-up. When the paper size is A4, Let-
ter or Legal, normal mode, rough paper mode, and OHT mode are selectable as the fix-
ing mode based on the command from the controller. When other paper sizes are used,
the universal mode is selected automatically, and other modes cannot be selected.
2 - 11
CHAPTER 2
A4/Letter/Legal
Other Sizes
Paper size
600DPI
Normal mode
OHT mode
Universal mode
Normal mode
Universal mode
Resolution
1200DPI
Rough paper mode Rough paper mode