Panasonic KX-FP362BX, Service Manual

Page: 131 / 196

7.4.3. 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 thermalhead
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 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 increment is synchronized at IC520 pin 39 (NEWTHCLK), and sent from IC520
pin 40 (NEWTHDAT) 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 IC520 pin 38
(NEWTHLAT).
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 IC520 pins 44 and 45, 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, NEWSTB1 to NEWSTB2, impress as required for one-line printout.
When the thermal head is not used, the IC501 pin 137 (THON) becomes low, Q501 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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KX-FP362BX