Kyocera Mita DC-1560, Service Manual

Page: 97 / 289

1AF
2-3-8
2-3-3 Operation unit PCB
P G
S
24 V DC
Source driver
Sink driver
5 V DC
LEDs and 7-seg LEDs
Key switches
OPCB
MPCB
SEG a
DEG 0
KEY 0
SEG b
SEG c
SEG d
SEG e
SEG f
SEG g
SEG h
DEG 1
DEG 2
DEG 3
DEG 4
DEG 5
DEG 6
DEG 7
KEY 1
KEY 2
Figure 2-3-7 Operation unit PCB block diagram
The operation unit PCB (OPCB) consists of LEDs, 7-segment LEDs and key switches
arranged in matrix.
To light an LED or 7-segment LED, the main PCB (MPCB) turns on one of the source drivers
for lines SEG a to SEG h to allow current to the line on which the LED or 7-segment LED
to be lit is present. Scan signals which go low in sequence are constantly output to the sink
drivers for lines DEG 0 to DEG 7, so current flows through the LED for which the two signals
are low simultaneously.
The status of key switches is detected by return signals KEY 0 to KEY 2. When none of the
keys on the operation panel is pressed, each line of return signals KEY 0 to KEY 2 is pulled
high to 5 V DC by the main PCB (MPCB). The main PCB (MPCB) outputs scan signals that
go low in sequence to the sink drivers for lines DEG 0 to DEG 7, so, when a key is pressed,
the key switch conducts and the return signal goes low due to the scan signal. The main PCB
(MPCB) identifies the specific key by the location of the cross point where the line emitting
the scan signal and the line with the low return signal meet.