Panasonic KX-FT21BX Service Manual page 148

KX-FT21LA
4-2. THERMAL HEAD
(1) Function
This unit utilizes state of the art thermal printer technology.
The recording paper (roll paper) is chemically processed. When the thermal head contacts this paper it emits heat
momentarily, and black dots (appearing like points) are printed on the paper. If this continues, letters and/or diagrams
appear, and the original document is reproduced.
COMPOSITION OF THE RECEIVE RECORD SECTION (THERMAL RECORDING FORMAT)
(2) Circuit Operation
There are 9 driver ICs aligned horizontally on the thermal head and each one of these ICs can drive 192 heat emitting
registers. 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 166 (THCLK), and sent from IC1 pin
163 (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 increment 1728, all the shift registers become filled with data, and a latch pulse is emitted to each IC from IC1 pin 167
(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 (159, 160) 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 three line strobes, STB1 to 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 207. (See page 116.) Depending on that value, the strobe width is recorded in ROM (IC2).
Accordingly, the strobe width is determined.
When the thermal head is not used, the IC1 (170, THON) becomes low, Q8 turns OFF, Q13 turns OFF, and the +24 V
power supply for the thermal head driver is not impressed to protect the IC.
Platen Roller
Thermal Recording Paper
Thermal Head
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