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© 2001-11 PRINTED IN JAPAN
B51-7859-00 (S) 1929
SERVICE MANUAL
CASSETTE RECEIVER
KRC-791/Y
KRC-791
MTL/M.RDM
PROG/PTY
EX
50Wx4
DOLBY B NR
B NR
LOUD
SCAN
B.S/RDM
REP
DISP
NAME.S
TI
VOL ADJ
OFF
AUD
MENU
CLK
ANG
DAB
Front glass
(B10-4156-01)
Knob(1-6)
(K25-1405-02)
Knob(SRC)
(K24-3835-04)
Knob(FM,AM)
(K25-1406-03)
Knob(VOL)
(K25-1404-03)
Panel assy
(A64-2577-02)
Knob(UP,DW)
(K25-1408-03)
DC cord
(E30-4942-05)
Remote controller assy
(A70-0886-15)
Antenna adaptor
(T90-0523-05)
Screw set
(N99-1704-05)
T
orsion coil spring
(G01-2924-04)
Lever
(D10-4562-04)x2
Mounting hardware assy
(J21-9716-03)
Remote controller assy
(A70-2025-05)
Plastic cabinet assy
(A02-1497-13)
MASK-key
Knob(PROG)
(K25-1407-03)
Front glass
(B10-4222-03)
The CASSETTE MECHANISM OPERATION DESCRIPTION is the same model D40-1122-05.
Please refer to the service manual for model D40-1122-05(B51-7542-00).


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KRC-791/Y
2
BLOCK
DIAGRAM
ILL
TEL MUTE
ACC
ANT CON
P CON
BACK UP
EXT AMP CONT
FM+B
BUFFER
BUFFER
DECODER
RDS
IC11
IC2
E-VOL
MPX
N.C.
AM+B
SYSTEM u-COM
IC1
KEY
MATRIX
RESET
SW
LCD
DRIVER
REMO
G/R SW
RESET
IC15
MOTHER u-COM
LCD TYPE
IC1
DRIVER
SUB MOT
IC13
MAIN MOT
AVR
SUB MOT
AVR
ILL AVR
A 8V
IC3
SW14V
EXT AMP CONT
DIMMER
ACC DET
TEL MUTE
P CON
B.U DET
ANT CON
SW5V
B.U.5V
P-5V
Q21,22
SRM
MECH
POWER IC
THERMO
PROTECT
IC4
IC10
MUTE LOGIC
DRIVER
MUTE
Q1-4
SP OUT
1.8V PRE OUT
LCD
ANT.
DET
SRM MECH
IC2
Q39
Q32
Q45
Q25
Q26,27
Q28-31
Q24
Q23
Q36
Q33,34
Q37,38
Q41,42
Q3,4
Q73
Q90
Q88
Q89
AUDIO
S-METER
IFC OUT
PLL DATA
PLL CLK
SW5V
FM
AM
TAPE
CHANGER
S METER
QUAL
SD
A
SCK
S MUTE
A 8V
MODE 2
SUB-
MOT+B
SUB+
MODE 1
MS MODE
F/R
MUTE
MTL ON/OFF
BOLBY B/C
DOLBY ON/OFF
MS OUT
R REEL
F REEL
MODE 3
TAPE IN
SRM
SW2
SRM
SW1
RCLK
QUAL
RDATA
NOISE
S METER
IFC
IFC OUT
PLL DATA
PLL CLK
MS OUT
MTL ON/OFF
MODE 2
MODE 3
R REEL
MODE 1
F REEL
MS MODE
F/R
MUTE
DOLBY ON/OFF
DATA C
CH RST
CH MUTE
DOLBY B/C
DATA H
CH CON
CH CLK
REQ H
REQ C
TAPE IN
SRM
DET
RESET
SUB
MO
T2
SUB
MO
T1
SUB
MO
T3
CASS/SRM
M
OTO
R
ILL
ON
AM+B
FM+B
SCK
SD
A
PRE MUTE
MUTE
BEEP
P MUTE
ACC DET
PHONE
DIMMER
EXT AMP CONT
P CON
P-5V
P ON
ANT CONT
B.U DET
SW5V
SW5V
3
3
13
CH MUTE
CH RST
DATA H
DATA C
CH CON
REQ C
CH CLK
REQ H
BACK UP
8
1200mV
388mV
A 8V
SW5V
PANEL5V
2
B.U.5V
4
2
SUB+
SUB-
2
SUB-
SUB+
MOT+B
A8V
PAN5V
B.U.5V
SW5V
MUTE
A
C
GND
BACK UP
SW5V
B.U.5V
B.U.5V
CH
FM
1800mV
TAPE
AM
3600mV
855mV
1372mV
600mV
3600mV
1800mV
E TYPE
K TYPE
1800mV
SW5V
245mV(ETYPE)
460mV(KTYPE)
FM:
AM:
170mV
TUNER
CASSETTE MECHA
CD-CHANGER
MD-CHANGER
(X16-154X-XX)


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KRC-791/Y
3
COMPONENT DESCRIPTION
q SWITCH UNIT(X16-154X-XX) (X16-189X-XX)
Component
Purpose · Function
Operation · Conditions · Compatibility
IC1
LCD DRIVER with Key Matrix
IC2
Remote Control IC
Q1
Key Detection SW
Q2 starts key scan in M&T.
Q3,4
Key Illumination SW
Lights key illumination in Red when the base of Q3 is ON.
Lights key illumination in Green when the base of Q4 is "H"
Q5
VLCD Reference Voltage Supply
Constant voltage circuit.
Q6
Remote Control IC Power Supply Activates remote control when the base of Q6 is "L".
Q7
Dimmer SW
The base of Q7 is normally "H" but becomes "
" when DIMMER is ON.
q SYNTHESIZER UNIT(X14-6442-7X) (X14-6452-XX)
Component
Purpose · Function
Operation · Conditions · Compatibility
IC1
System
µ-com
IC2
E-VOL, N.C, MPX
IC3
Regulator IC for Audio 8V
IC4
Power IC
IC10
Mute logic IC
IC11
RDS decoder
IC13
Motor driver IC
IC15
Reset IC
Q1~4
PRE OUT MUTE SW
Pre outs are muted when the base goes "H".
Q18~20
Audio 8V AVR
Inverted darlington connection
Q20 is turned ON when Q18's base goes "H".
Q21, 22
B.U 5V AVR
Inverted darlington connection
Q22 is turned ON when Q21's base goes "H".
Q23
SW 5V
ON when the base goes "L".
Q24
B.U detection
ON when the base goes "H" during B.U applied.
Q25
ACC detection
ON when the base goes "H" during ACC applied.
Q28~31
P-CON SW
Q28 is turned ON when Q31's base goes "H".
Q32
Dimmer SW
ON when the base goes "H" while vehicle small lamps turn on.
Q33,34,44
Illumination AVR
ON when Q44's base goes "H".
Q36
SW 14V
ON when base goes "H".
Q37,38
Motor driver supply
Q38 is turned ON when Q37's base goes "H".
Q39
External Amp Control
ON when the base goes "L".
Q41, 42
Cassette mecha main motor supply SW Q42 is turned ON when Q41's base goes "H".
Q43
Motor driver's voltage SW
Base "H" ··· cassette mecha's submotor
Base "L" ··· mask mecha's motor.
Q45,46
Panel 5V SW
Q45 is turned ON when Q46's base goes "H".
Q71
Pre out mute driver
ON when the base goes "L".
Q72
E-VOL Mute SW
ON when the base goes "H".
Q73
Noise buffer
Q85
IFC out buffer
Q86,88
AM+B SW
Q88 is turned ON when Q86's base goes "H".
Q87,89
FM+B SW
Q89 is turned ON when Q87's base goes "H".
Q90
Composite out buffer
q DOLBY UNIT(X87-3022-7X)
Component
Purpose · Function
Operation · Conditions · Compatibility
IC1
Playback EQ, Dolby & Blank Detection
Q1
Constant Switching in Blank Detection
Switches the time constant according to the PLAY or FF/REW mode.


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KRC-791/Y
4
MICROCOMPUTER'S TERMINAL DESCRIPTION
q UPD703033GC138 (IC1: X14-)
SYSTEM MICROCOMPUTER
Pin
Name
I/O
Purpose
Operation Description
1
AM+B
O
AM power supply terminal.
During AM operation: H.
2
FM+B
O
FM power supply terminal.
During FM operation: H.
Last FM with RDS model: H
3
AFS
O
Constant switching when noise is detected.
During FM seek or AM search: L.
During reception: H.
4
PLL-DATA
I/O DATA input/output terminal from/to F/E.
5
PLL-CLK
I/O CLOCK input/output terminal from/to F/E.
6
Evdd
-
Positive power supply terminal.
7
GND
-
Grounding terminal.
8
N.C
O
No connection.
9
BEEP
O
Beep output terminal.
10
REMO
I
Remote control input terminal.
11
P-ON
O
SW 14 V control terminal.
Power ON: H. Power OFF: L.
12
P-STBY
O
Power IC STBY terminal control.
Power IC OFF: L. Power IC ON: H.
During reset: Input.
13
IC2-SDA
I/O IC2 DATA line.
14
IC2-SCK
O
IC2 CLOCK line.
15
P-MUTE
O
Power IC muting terminal.
Power OFF: L. All OFF: L.
During TEL muting: L.
16
PRE-MUTE
O
Pre-Out muting terminal.
During momentary power down: L.
17
D/A-SDA/DIM-CON
O
D/A data line. (V-LED)
18
TEST
-
Test pin.
19
P-CON
O
Power control terminal.
Power ON: H. Power OFF: L.
20
ANT-CON
O
Antenna control terminal.
TUNER, TI ON: H
21
MUTE
O
Muting terminal.
ON: Open. OFF: L.
The time constant is 0.48 ms with all models.
22
N.C
O
No connection.
23
ACC-DET
I
Acc detection terminal.
Acc detected: L. Acc not detected: H.
24
DIMMER
I
Small detection terminal.
ON: L. OFF: H.
25
SW-5V
O
5 V power supply terminal.
ON: L. OFF: H.
26
CH-MUTE
I
Muting request from CH.
ON: H. OFF: L.
27
CH-CON
O
CH control output.
ON: H. OFF: L.
28
CH-REQH
O
Request output to CH.
Requested: L.
29
CH-RST
O
Reset output to CH.
Normal: L. When the system is reset, turns H then
L in 400 ms after recovery from reset.
30
EXT-AMP-CONT
O
External amplifier control terminal (In 200 ms).
L 40 ms: Bass boost OFF. L 70 ms: Bass boost LOW.
L 100 ms: Bass boost HIGH.
31
RESET
I
Reset input terminal
Normal: H. Reset: L.
32
XT1
I
Sub-clock connection terminal.
The clock count is active even when Power is OFF.
33
XT2
-
Sub-clock connection terminal.
34
REGC
-
Output terminal for the capacitor in the regulator
in
µ-COM.
35
X2
-
Main clock connection terminal.
Power ON: Oscillated.
Power OFF or momentary power down: Oscillation stopped.
36
X1
I
Main clock connection terminal.
37
Vss
-
Grounding terminal.
38
Vdd
-
Positive power supply terminal.
39
CLKOUT
O
Internal System Clock output.
40
N.C
O
No connection.
41
MOTOR
O
Cassette mechanism main motor output terminal.
When the motor is running: H.
When it is stopped: L.
42
MODE3
I
Cassette mechanism mode detection terminal.
43
MODE1
I
Cassette mechanism mode detection terminal.
44
MODE2
I
Cassette mechanism mode detection terminal.
45
N.C
O
Outputs Low. No connection.
46
SUB1
O
Sub-motor output terminal (1).


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KRC-791/Y
5
MICROCOMPUTER'S TERMINAL DESCRIPTION
Pin
Name
I/O
Purpose
Operation Description
47
SUB2
O
Sub-motor output terminal (2).
48
SUB3
O
Sub-motor output terminal (3).
49
CAS/SRM
O
Cassette mechanism/SRM mechanism
Cassette mechanism: H.
voltage switching terminal.
SRM mechanism: L.
50
N.C
O
Outputs Low.
No connection.
51
N.C
O
Outputs Low.
No connection.
52
ILL-ON
O
FL +B output terminal.
ON: H, OFF: L
53
PAN-5V
O
Panel 5 V control terminal.
Panel detected: H
Panel not detected: L
54
N.C
O
Outputs Low.
No connection.
55
BVdd
-
Positive power supply terminal.
56
BVss
-
Grounding terminal.
57
TYPE1
I
Destination type switching port.
58
TYPE0
I
Destination type switching port.
59
N.C
O
Outputs Low. No connection.
60
N.C
O
Outputs Low. No connection.
61
ST TYPE1
I
IC2 destination type terminal.
Default: L.
62
ST TYPE0
I
IC2 destination type terminal.
Default: L.
63
SRM-SW1
I
Panel position detection switch 1.
64
D/A-SDA
O
D/A clock line. (V-LED)
Panel detached: L.
Momentary power down: L.
65
L CE
I/O CE terminal for LCD driver.
66
SRM-SW3
I
Panel position detection switch 3.
67
SRM-SW2
I
Panel position detection switch 2.
68
FWD/REV
O
TAPE EQ input switching terminal.
FWD: L. REW: H.
During TAPE PLAY: H.
69
MS-CONT
I/O
Constant switching terminal in case of blank
During TAPE FF/REW or other than TAPE input: L.
detection.
Cassette mechanism detected: L.
Cassette mechanism not detected: H.
70
AVCONT
O
AD reference voltage control output.
Same timing as P-ON. H during operation.
71
Avdd
-
Positive power supply terminal.
72
Avss
-
Grounding terminal.
73
Avref
I
Reference voltage supply terminal for A/D converter.
74
PHONE
I
PHONE detection terminal.
TEL MUTE: No more than 1 V.
NAVI MUTE:2.5 V or more.
75
R-REEL
I
Cassette mechanism reel pulse input (REV).
Vth = 2.5 V.
76
F-REEL
I
Cassette mechanism reel pulse input (FWD).
Vth = 2.5 V.
77
N.C
I
No connection.
Connected to GND.
78
SRM-DET
I
SRM mechanism detection.
SRM mechanism detected: L.
79
NOISE
I
FM noise detection terminal.
Model without RDS: Connected to GND.
80
S-METER
I
Signal meter detection terminal.
81
R-DATA
I
RDS decoder DATA input terminal.
Model without RDS and
RBDS: Connected to GND.
82
R-QUAL
I
RDS decoder QUAL input terminal.
Model without RDS and
RBDS: Connected to GND.
83
IFC-OUT
I
F/E IFC OUT input terminal.
Station detected: L.
84
MUSIC
I
Music blank detection input.
Music signal detected: L.
Music signal not detected: H.
85
PACK-DET
I
Cassette mechanism pack detection terminal.
Cassette pack detected: L.
Cassette pack not detected: H.
86
DOLBY
O
Dolby ON/OFF switching.
ON: H. OFF: L.
87
R-CLK
I
RDS decoder CLK input terminal.
Model without RDS and
RBDS: Connected to GND.
88
CH-REQC
I
Request input from CH.
ON: L.
89
KEY REQ
I
Communication request from LCD driver.
90
N.C
I
No connection.
Connected to GND.
91
EQ-MUTE
O
EQ muting switching.
During TAPE PLAY: L. During TAPE FF/REW: H.
Other than TAPE input: H.