Panasonic KX-F900 Service Manual page 139

KX-F900
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 momen
tarily, black dots (appearing almost as a point) are printed on the paper. If this point is continued, litters and/or diagrams
appear, and the original document is reproduced.
COMPOSITION OF THE RECEIVE RECORD SECTION (THERMAL RECORDING FORMAT)
Platen Roller
Thermal Recording Paper
T
Thermal Head
(2)Circuit Operation
There are 18 driver ICs aligned horizontally on the thermal head and each one of these ICs can drive 96 heat emitting
registers. This means that one line is at a density of 96 )< 18=1728 dots=(8 dots/mm).
White/Black (white=0, black=l) data in one line increments is synchronized at IC1 pin 24 (THCLK) and sent from IC1 pin
22 (THDAT) to the shift register of the fCs. The shift registers of the 18 tCs are connected in series, and upon shift of 1728
dot increment, all the shift register become filled with data, and a latch pulse is emitted to each IC from IC1 pin 23
(THLAT).
With this latch pulse, all the contents of shift registers are latched to the latch registers. Thereafter, through the addition of
strobe from the IC1 pins (25, 26, 27, 28) only dot of location of black (=1) among latched data activates driver, and current
passes to heat emitting body to cause heat emission.
Here the strobe of four lines STB1 to STB4 impresses at intervals of 9.216 msec, as required for one-line printout, for
each 1/4th of 18 IC unit (4 unit or 5 unit) upon each time interval divided into four equal increments.
The sequence is as shown below. [Moreover, in the case of strobe width, the resistance value of the thermistor inside the
thermal head is constantly detected by IC1 pin 38, and vales from the ROM (IC2) table corresponding to temperatures
eliminate temperature changes of density through setting by CPU.]
When the thermal head is not used, the IC1 (119, TH-POWER) becomes low level, IC7 becomes OFF, RL201 breaks, and
the +24 V power supply for the thermal head driver is not impressed to protect the IC.
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