Panasonic KX-FM89BX, Service Manual

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149 (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 IC501 pin 151 (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 IC501 pins (142, 143), only the dot location of
black (=1) among latched data activates the driver, and the current
passes to heat the emitting body to cause heat emission.
Here, the two 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 IC501 pin 2. Depending on that value, the
strobe width is recorded in ROM (IC502). Accordingly, the strobe
width is determined.]
When the thermal head is not used, the IC501 (141, THON)
becomes low , Q502 turns OFF, IC506 turns OFF, and the +24V
power supply for the thermal head driver is not impressed to
protect the IC.
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