Service manual

2DA/2DB-1
2-3-18
2-3-5 Operation unit PCB
Figure 2-3-9 Operation unit PCB block diagram
The operation unit PCB (OPPCB) consists of key switches, LEDs and buzzer. The lighting of LEDs is determined by scan
signals (SCAN0 to SCAN7) and LED lighting selection signals (LED0 to LED4) from the main PCB (MPCB). The key
switches operated are identified by the scan signals (SCAN0 to SCAN7) and the return signals (KEY0 to KEY9).
As an example, to light L1, the LED lighting selection signal (LED4) should be driven low in synchronization with a low level
on the scan signal (SCAN0). LEDs can be lit dynamically by repeating such operations.
As another example, if K1 is pressed, the corresponding key switch is turned on feeding the low level of the scan signal
(SCAN0) back to the main PCB (MPCB) via the return signal (KEY9). The main PCB (MPCB) locates the position where the
line outputting the scan signal and the line inputting the return signal cross, and thereby determines which key switch was
operated.
YC1
YC2
SGND
+5V
BUZERDRN
SCAN0
SCAN1
SCAN2
SCAN3
SCAN4
SCAN5
SCAN6
SCAN7
1
2
3
4
5
6
7
8
9
10
11
1
2
3
4
5
6
7
8
9
10
11
KEY0
KEY1
KEY2
KEY3
KEY4
KEY5
KEY6
KEY7
KEY8
KEY9
LED4
LED3
LED2
LED1
LED0
POWERKEY
L10L14 L1
L2L6
L3L7
L4L6
L5L9
L20L25L1L35
L11L15L21L26L31L36
L12L16L22L27L32L37
L13L17L23L28L33L38
L40
BZ1
SGND
SGND
SGND
R1
L43
L42
L41
L19L18L24L29L34L39
+5V
K50
D1 D2 D3 D4 D5 D6 D7 D8 D9
K53 K41 K30 K22 K12 K6 K1
K51 K54 K42 K31 K23 K13 K7 K2
K52 K55 K43 K32 K24 K14 K8 K3
K56 K57 K44 K33 K25 K15 K9 K4
K60 K58 K45 K35 K26 K18 K10 K5
K64 K59 K46 K36 K27 K19 K11 K34
K65 K51 K47 K37 K28 K20 K16 K40
K66
K69
K62 K48 K38 K29 K21 K17
K67 K63 K49 K39
+5V
K68