Epson Stylus COLOR 900 Service Manual page 55

EPSON Stylus COLOR 900/900N
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AN7 (Pin 112)
TH1 is located on the main board and monitors the temperature of
the two pre-driver ICs (the head driver ICs: IC15 and IC16). These
pre-driver ICs produce the high-frequency trapezoidal waveform
that drives the printhead. If TH1 detects an unexpected rise in
temperature, it causes the printer to stop printing.
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AN6 (Pin 111)
Four power transistors (Q3 - Q6) used to generate the trapezoidal
waveform are attached to a large heat sink on the main board. The
heat sink is equipped with a cooling fan, which can be turned on or
off by the CPU. The CPU receives temperature data through its AN6
port from a thermistor mounted directly on the heat sink. This lets
the CPU control the cooling fan's operation.
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AN5 (Pin 110)
This port receives temperature signals from a thermistor built into
the printhead. Based on these signals, the printer makes subtle
changes in the voltage level of the head drive trapezoidal waveform,
enabling the printer to eject the correct amount of ink at any
temperature.
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AN0-AN4 (Pins 1, 2, 9, 10, 4)
Five temperature sensors in the printhead (one for each row of
nozzles) report directly to the nozzle selector IC (also located in the
printhead). The nozzle selector IC, in turn, relays this information to
the CPU through ports AN0-AN4. If the printhead is driven without
ink being ejected, the temperature inside the printhead can rise
above 100 °C. These sensors prevent the printhead from being
damaged as a result.
Chapter 2 Operating Principles
50