Read Panasonic KX-T7440CB / KX-T7440C Service Manual online
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KX-T7440C/KX-T7440C-B
6. LED CIRCUIT KEY INPUT CIRCUIT
1) Circuit Operation
A drive pulse wave, as in Fig. 1, is output by IC3. That signal goes through the drive digital transistor and connects the key
button and LED cathode. By pressing the key, the drive pulse wave is input to the keyboard. In order to light the appropriate
LED, the LED control port is turned ON. That result LED is lit by the pulse driver.
A drive pulse wave, as in Fig. 1, is output by IC3. That signal goes through the drive digital transistor and connects the key
button and LED cathode. By pressing the key, the drive pulse wave is input to the keyboard. In order to light the appropriate
LED, the LED control port is turned ON. That result LED is lit by the pulse driver.
5V
LED
ON/OFF
CONTROL
ON/OFF
CONTROL
PULSE
OUTPUT
OUTPUT
KYE
INPUT
INPUT
LED
L [0] ~ L [27]
C [0] ~ C [7]
K [0] ~ K [8]
IC3
A
B
C[0]
C[1]
C[2]
C[3]
A Each Cannel's Pulse Output
Fig. 1
Fig. 2
A and B 's Wave
Circuit Diagram
A
B
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