Panasonic KX-FC255CX-S, Service Manual

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KX-FC255CX-S
6.4.3. Thermal Head
1. Function
This unit utilizes the state of the art thermal printer technology.
The ink film is chemically processed. The ink film is comprised of two parts: an ink layer and a base film. When the thermal
head contacts this ink film, it emits heat momentarily, and the ink layer is melted and transferred to the paper. If this continues,
letters and/or diagrams appear, and the original document is reproduced.
2. Circuit Operation
Refer to the block diagram and the timing chart on the following page.
There are 9 driver ICs aligned horizontally on the thermal head and each one of these ICs can drive 192 heat-emitting regis-
ters. This means that one line is at a density of 192
×
9=1728 dots=(8 dots/mm).
White/Black (white=0, black=1) data in one line increment is synchronized at IC10 pin 117 (THCLK), and sent from IC10 pin
116 (THDAT) to the shift register of the ICs. The shift registers of the 9 ICs are connected in series, and upon the shift of the
1728 dot increment, the shift register becomes filled with data, and a latch pulse is emitted to each IC from IC10 pin 118
(THLAT).
With this latch pulse, all the contents of the shift registers are latched to the latch registers. Thereafter, through the addition of
strobes from the IC10 pins (103, 104), only the dot location of black (=1) among latched data activates the driver, and the cur-
rent passes to heat the emitting body to cause heat emission.
Here, the two line strobes, STB1 and STB2, impress at intervals of 9.216 msec, as required for one-line printout.
The sequence is shown on the next page. [Moreover, for the strobe width, the thermistor value inside the thermal head is
detected according to IC10 pin 4. Depending on that value, the strobe width is recorded in FLASH ROM (IC16). Accordingly,
the strobe width is determined.]
When the thermal head is not used, the IC10 (17, THON) becomes low, Q603 turns OFF, Q401 turns OFF, and the +24V
power supply for the thermal head driver is not impressed to protect the IC.