Kenwood KRC-791 Service Manual

CASSETTE RECEIVER

KRC-791/Y

SERVICE MANUAL

B51-7859-00 (S) 1929

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).

Panel assy (A64-2577-02)

DC cord (E30-4942-05)

50Wx4

Knob(VOL) (K25-1404-03)

Front glass (B10-4156-01)

KRC-791

B NRLOUD SCAN B.S/RDM REP

Knob(1-6) (K25-1405-02)

Remote controller assy (A70-0886-15)

Knob(FM,AM) (K25-1406-03)

DOLBY B NR

PROG/PTY

MTL/M.RDM

TI VOL ADJ

Knob(SRC) (K24-3835-04)

DISP NAME.S

OFF AUD

Knob(UP,DW) (K25-1408-03)

Antenna adaptor (T90-0523-05)

Knob(PROG) (K25-1407-03)

DAB ANG

CLK

Front glass (B10-4222-03)

Screw set (N99-1704-05)

Plastic cabinet assy (A02-1497-13)

Lever (D10-4562-04)x2

MASK-key

orsion coil spring

(G01-2924-04)

Remote controller assy (A70-2025-05)

Mounting hardware assy (J21-9716-03)

ILL TEL MUTE

ACC ANT CON P CON

BACK UP

EXT AMP CONT

FM+B

BUFFER

DECODER

RDS

IC11

IC2

E-VOL

MPX

N.C.

AM+B

SYSTEM u-COM

IC1

KEY

MATRIX

RESET

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

TAPE CHANGER

S METER

QUAL

SDA

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 MOT2

SUB MOT1

SUB MOT3

CASS/SRM

MOTOR

ILL ON

AM+B

FM+B

SCK

SDA

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

CH MUTE

CH RST

DATA H

DATA C

CH CON

REQ C

CH CLK

REQ H

BACK UP

1200mV

388mV

A 8V

SW5V

PANEL5V

B.U.5V

SUB+ SUB-

SUB-

SUB+

MOT+B

A8V

PAN5V

B.U.5VSW5V

MUTE

AC GND

BACK UP

SW5V

B.U.5V

1800mVTAPE

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)

KRC-791/Y

BLOCK DIAGRAM

KRC-791/Y

COMPONENT DESCRIPTION

● SWITCH UNIT(X16-154X-XX) (X16-189X-XX)

Component

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

Q5 Q6 Q7 Dimmer SW The base of Q7 is normally "H" but becomes "

● SYNTHESIZER UNIT(X14-6442-7X) (X14-6452-XX)

Component

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

Q21, 22 B.U 5V AVR

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

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

Q43 Motor driver's voltage SW

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

Purpose • Function Operation • Conditions • Compatibility

Lights key illumination in Red when the base of Q3 is ON.

Lights key illumination in Green when the base of Q4 is "H" VLCD Reference Voltage Supply Remote Control IC Power Supply

Purpose • Function Operation • Conditions • Compatibility

Illumination AVR ON when Q44's base goes "H".

Cassette mecha main motor supply SW

Constant voltage circuit.

Activates remote control when the base of Q6 is "L".

Inverted darlington connection

Q20 is turned ON when Q18's base goes "H".

Inverted darlington connection

Q22 is turned ON when Q21's base goes "H".

Q42 is turned ON when Q41's base goes "H".

Base "H" ··· cassette mecha's submotor

Base "L" ··· mask mecha's motor.

" when DIMMER is ON.

● DOLBY UNIT(X87-3022-7X)

Component

IC1

Purpose • Function Operation • Conditions • Compatibility

Playback EQ, Dolby & Blank Detection Constant Switching in Blank Detection

Switches the time constant according to the PLAY or FF/REW mode.

KRC-791/Y

MICROCOMPUTER'S TERMINAL DESCRIPTION

● 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.

3 AFS O Constant switching when noise is detected. 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. 13 IC2-SDA I/O IC2 DATA line.

14 IC2-SCK O IC2 CLOCK line. 15 P-MUTE O Power IC muting terminal. 16 PRE-MUTE O Pre-Out muting terminal. During momentary power down: L.

D/A-SDA/DIM-CON 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. 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.

EXT-AMP-CONT

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 -

35 X2 - Main clock connection terminal. 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. 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).

O D/A data line. (V-LED)

O External amplifier control terminal (In 200 ms).

During FM operation: H. Last FM with RDS model: H During FM seek or AM search: L. During reception: H.

Power IC OFF: L. Power IC ON: H. During reset: Input.

Power OFF: L. All OFF: L. During TEL muting: L.

ON: Open. OFF: L. The time constant is 0.48 ms with all models.

Normal: L. When the system is reset, turns H then L in 400 ms after recovery from reset. L 40 ms: Bass boost OFF. L 70 ms: Bass boost LOW. L 100 ms: Bass boost HIGH.

Output terminal for the capacitor in the regulator in µ-COM.

Power ON: Oscillated. Power OFF or momentary power down: Oscillation stopped.

When the motor is running: H. When it is stopped: L.

KRC-791/Y

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 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) 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.

69 MS-CONT I/O

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

74 PHONE I PHONE detection terminal. 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.

82 R-QUAL I RDS decoder QUAL input terminal. 83 IFC-OUT I F/E IFC OUT input terminal. Station detected: L. 84 MUSIC I Music blank detection input. 85 PACK-DET I Cassette mechanism pack detection terminal. Cassette pack detected: L.

86 DOLBY O Dolby ON/OFF switching. ON: H. OFF: L. 87 R-CLK I RDS decoder CLK input terminal. Model without RDS and

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.

Cassette mechanism/SRM mechanism Cassette mechanism: H. voltage switching terminal. SRM mechanism: L.

Panel detached: L. Momentary power down: L.

During TAPE PLAY: H. 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.

Reference voltage supply terminal for A/D converter.

TEL MUTE: No more than 1 V.

NAVI MUTE:2.5 V or more.

Model without RDS and

RBDS: Connected to GND.

Model without RDS and

RBDS: Connected to GND.

Music signal detected: L.

Music signal not detected: H.

Cassette pack not detected: H.

RBDS: Connected to GND.

During TAPE PLAY: L. During TAPE FF/REW: H.

Other than TAPE input: H.

KRC-791/Y

MICROCOMPUTER'S TERMINAL DESCRIPTION

Pin Name I/O Purpose Operation Description

92 MTL O NORMAL/METAL switching. NORMAL: H. METAL: L. 93 BU-DET I Momentary power down detection terminal. 94 CH-DATAC I DATA input terminal from CH.

95 CH-DATAH O DATA output terminal to CH. 96 CH-CLK I/O CLOCK input/output terminal from/to CH. 97 L-DATA L I DATA line from LCD driver. 98 L-DATA S I/O DATA line to LCD driver. 99 L-CLK I/O CLK line to LCD driver. Panel detected: L

100 N.C O Outputs Low. No connection.

Back-Up detected: L Back-Up not detected (momentary power down): H.

TEST MODE

M&T-SRT Model Test Mode

1. How to enter the test mode

• While holding the FM and Preset 6 keys, reset the unit.

2. How to exit from the test mode

• While holding the Preset 6 key, reset the unit.

• (Note) The test mode cannot terminated by Acc OFF, power OFF or momentary power down.

3. Initial status in the test mode

• Sources: All OFF.

• Display: All segments are lit.

• Volume: -10 dB (displayed as 30)

• Loudness: OFF

• CRSC: OFF regardless of the presence of switching function.

• SYSTEM Q: Flat.

• Blank Skip: OFF. (C/R model)

• LED: White for no scanning. (VLCD model)

KRC-791/Y

7. Audio-related specifications

• A short press of the Q key initiates the audio adjustment mode.

• Pressing the ∗ key on the remote initiates the audio adjustment mode.

• Continuous holding of a remote control key is inhibited.

• Bass, Middle and Treble are adjusted in 3 steps of Min/ Center/Max with the Track Up/Down keys.

• Balance is adjusted in 3 steps of Left Max/Center/Right Max with the Track Up/Down keys.

• Fader is adjusted in 3 steps of Rear Max/Center/Front Max with the Track Up/Down keys.

• HPF is adjusted in 2 steps of Through/220 Hz with the Track Up/Down keys.

• LPF is adjusted in 2 steps of Through/120 Hz with the Track Up/Down keys.

• Bass f, Bass Q, Bass EXT, Middle f, Middle Q and Treble f are not dealt with by the audio adjustment.

4. Special display in Tuner mode

• When any of the following messages is displayed in Tuner mode, the front end may be abnormal.

• "TNE 2P NG": The EEPROM is set to the default (unstable values) because the F/E was shipped without passing through the adjustment process, etc.

• "TNCON NG": Communication with the F/E is not possible.

5. Forced switching of K3I

• Each press of the Preset 6 key in Tuner mode should switch K3I from AUTO → Forced Wide → Forced Middle → Forced Narrow → AUTO. The initial status is AUTO and the display shows these modes as follows.

• AUTO : FMA

• Forced Wide : FMW

• Forced Middle : FMM

• Forced Narrow : FMN

6. Test mode specifications of the CD receiver

• Forced ejection is inhibited in the reset start operation. When the unit is reset while a CD is loaded in it, the CD is not recognized by resetting.

• Each press of the Track Up key jumps to the following track numbers. No. 9 → No. 15 → No. 10 → No. 11 → No. 12 → No. 13 → No. 14 → No. 9 (The cycle restarts from here.)

• Each press of the Track Down key jumps to the previous track number to the track being played.

8. Menu-related specifications

• A short press of the CLK key initiates the Menu mode.

• Pressing the DNPP/SBF key on the remote initiates the Menu mode.

• Continuous holding of a remote control key is inhibited.

• Calendar adjustment, calendar display switching and calendar memo are eliminated from the targets of continuous key holding. (FL model).

• In the color adjustment mode, pressing the Preset 1 key sets Red, 2 sets Blue, 3 sets Green and 4 sets Green. (VLCD model)

• Contrast is adjusted in 3 steps of 0/5/10 and the default is 5. (VLCD/LCD model)

• Brightness is adjusted in 3 steps of 0/5/10 and the default is 10. (Normal FL model)

9. Backup current measurement

• When the unit is reset while Acc is OFF (i.e. by turning Back-Up ON), the MUTE terminal goes OFF in 2 seconds in place of 15 second. (The panel, CD mechanism and TAPE mechanism are not activated at this time.)

KRC-791/Y

TEST MODE

10. Special display when the display is All ON

Pressing the Preset keys while the power is All OFF displays the following information.

Version display (8 digits, Month/Day/Hour/Minute)

PRESET1 (Display)

SYS xxxxxxxx System microcomputer PAN xxxxxxxx Panel microcomputer

PRESET2

PRESET3 Long press/hold: Clear power ON time.

PRESET4

PRESET5 Long press/hold: Clear TAPE/CD/MD ejection

PRESET6 Long press/hold: Clear Panel open/close count.

Serial No. display (8 digits) (Note) CD/R K type eXcelon model (Display) SNo. xxxxxxxx Short press: View power ON time. (The All OFF period is not counted.)

(Display) PonTim xxxxx Max. 65535 (hours) Short press: Display TAPE/CD/ MD operation time. Long press/hold: Clear TAPE/CD/MD operation time. (Display) CDTime xxxxx (CD/R) TapTim xxxxx (C/R) Max. 65535 (hours) Short press: Display TAPE/CD/ MD ejection count.

count. (Display) EjeTim xxxxx Max. 65535 (times) Short press: Display Panel open/close count.

(Display) PnCnt xxxxx Max. 655350 (times)

11. Other specifications

• Automatic panel closing when a tape/CD is inserted is inhibited. (M&T model)

• Panel operation by turning power OFF/ON is inhibited. (M&T model)

• Pressing the ATT key opens or closes the panel. (M&T model)

• Messages such as "CODE OFF" are not displayed when power is turned ON.

• Pressing the TI (AUTO) key during changer operation turns 2zone ON. 2zone can be turned OFF by pressing the TI (AUTO) key again. The P/S dot lights while 2 zone is ON.

• Pressing and holding the CLK key for a second in the All OFF status the Mask Key (security) write mode.

■ Security-related information

• Forced Power ON mode (All models) Even when the security (Mask key) is approved, resetting the unit while holding the ATT and Preset 4 keys makes it possible to turn the power ON for 30 minutes. After 30 minutes have elapsed, it is not possible to return to the previous condition unless the unit is reset again.

• Method of registration of the security code after

EEPROM (Tuner Unit Ass'y) replacement (Code security model)

1.Enter the test mode. (See 1 How to enter the test mode)

2. Press the CLK key to enter the security registration

mode.

3.Enter the code using the Preset 1/2/3/4 keys.

Example: To enter "3510"

• Press the Preset 1 key 4 times.

• Press the Preset 2 key 6 times.

• Press the Preset 3 key twice.

• Press the Preset 4 key once.

4.Press and hold the DISP key for 3 seconds until

"APPROVED" is displayed.

5.Exit from the test mode. (See 2 How to exit from the

test mode) (Note) All Clear is not applicable to the security code of this model.

• Simplified method of clearing the security code

(K Type only)

1.While the code entry is requested, press and hold the

VOL UP key for 3 seconds while holding the DISP key pressed.(This should turn ---- off.)

2.Enter "KCAR" from the remote. (Same way as the 00

model) Press the 5 key on the remote twice, then press the Track Up key. (This enters "K") Press the 2 key on the remote 3 times, then press the Track Up key. (This enters "C") Press the 2 key on the remote once, then press the Track Up key. (This enters "A") Press the 7 key on the remote twice, then press the Track Up key. (This enters "R")

3.The security code is cleared and the unit enters the All

OFF mode.

4.If you commit a mistake in the code entry, the unit enters

the code request mode again.

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