Panasonic KX-FP70CX, Service Manual, Page: 24 / 211

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KX-FP701CX/KX-FP702CX
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 increments is synchronized at IC1 pin 117 (THCLK), and sent from IC1 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 dot incre-
ment 1728, all the shift registers become filled with data, and a latch pulse is emitted to each IC from IC1 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 IC1 pins (103, 104) only black dot locations (=1) among latched data activates the driver, and the
current passes to heat the emitting body causing 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 IC1 pin 4. Depending on that value, the strobe width is recorded in ROM (IC6).
Accordingly, the strobe width is determined.
When the thermal head is not used, the IC1 (17, THON) becomes low, Q502 turns OFF, Q401 turns OFF, and the +24 V
power supply for the thermal head driver is not impressed to protect the IC.