Sony UP-895, Service Manual

Page: 37 / 84

4-11
UP-895/(E)
4-4-7. Monitor of Head Temperature Sensor
The change in the resistance value of the thermistor inside a thermal head is converted into a voltage
using a head temperature detector circuit (IC401) and read by a system control (IC304). The voltage
value is converted from analog to digital. Density (gamma) correction, fan motor control for head
cooling, and head-in cleaning discrimination are performed according to the digital value.
4-4-8. Control of Head Fan Motor (for Head Cooling)
The head fan motor is operated when a system control (IC304) controls driving transistors (Q400 and
Q403). The head fan motor is turned on when the head temperature is more than approximately 50
d
C or
during printing.
Operation of head fan motor
IC304-26 pin Operation
L OFF
H ON
4-4-9. Control of Video Circuit Section
A system control (IC304) controls the video circuit section as shown in the table below.
IC304 I/O Function
77pin O Switches THRUE and EE signals. L: ON
H: OFF
59pin O Sets the trap filter to ON or OFF. L: ON
H: OFF
60pin O Selects NTSC or PAL. L: When an NTSC signal is input
H: When a PAL signal is input
53pin O Sets the AGC function to ON or OFF. L: ON
H: OFF