Kenwood KRC-851D User manual

STEREO
CASSETTE
RECEIVER
|
KE
NWOOD
KRC-851D
SERVICE MANUAL
©1990-2 PRINTED IN JAPAN
B51-6133-00(B)1602
Knob (TONE)
(K23-1004-04)
Panel assy
(A20-7551-03)
Escutcheon assy
(BO7-2014-12)
Knob (VOL)
(K29-5538-03)
Metallic cabinet
(AQ1-2508-21)
Detachble connector
(WO09-0715-04)

KRCO-851D
CONTENTS
TROUBLESHOOTING GUIDE.................0...... 2 PC. BOARD .iscscee noe tad eek ie ied vee Dae eek 31
CONNECTIONS ...........0.0 0200 e cece eee eee eee 3 SCHEMATIC DIAGRAM................-..000022005 39
DISASSEMBLY FOR REPAIR..................2.-.. 4 EXPLODED VIEW (MECHANISM).................. 49
BLOCK LEVEL DIAGRAM ..................00200 008 5 EXPLODED VIEW (UNIT) .....................00.00, 50
CIRCUIT DESCRIPTION .....................00 2s 6 PARTS HS 1-3. occcd.at ieahesienave sive cee gees 51
MECHANISM DESCRIPTION ..................-.0.. 20 SPECIFICATIONS ...................065 BACK COVER
ADJUSTMENT ......... 000s cece eee e eee ees 26
TROUBLE SHOOTING.................0....2.2 000. 28
TROUBLESHOOTING GUIDE
Other than the previous, this unit displays various error indications to show the
following messages.
E-0OO : CD-changer control output is not connected.
E-—0O1 :No disc magazine in the changer, or the magazine is not set completely.
E - 02 : No.discs in the disc magazine.
E-0O3 : The specified track is not present on the disc.
(Example : This appears when the 15th track is specified for a disc on
which only 10 tracks are contained.)
E— 04 : Disc is too dirty.
Condensation has occurred on the disc, or water drops are on the disc.
Disc is set upside down.
E-—0O5:Memory play switch is pressed with no memory.
E —- 99 : Operation incorrect due to something being defective.
Press the Reset button on the unit.
If the “E-99” indication does not disappear with this operation, consult
your nearest KENWOOD Service Agent.
E-OD: @When the temperature exceeds 60°C, the protection circuit is engaged
to stop any operation. At this time , this indication will appear.
@Open a window or tunn the air — conditioner ON to lower the
temperature. After a while, this indication will go out.
@This indication also appears for several seconds when making
connections, or when the Reset button is pressed.
E-OE: This is displayed when the condition of “E-OD” is released.
load: This indication appears while a disc is being changed inside the changer.
CAUTION : Memory play, Random play, Track repeat or Track scan cannot
be initiated while the load indication is displayed.
* When no indicator appears in this unit and only illumination appears, the cable
connector may nearly be disconnected.

KRC-851D
CONNECTIONS
@ Detachable case
p= [ | To FM/AM antenna
til
IN
et
:
(O>
CT
inout
es
tpt
i
Power
amplifier
Rear
(optional)
speakers
Front
(7)
=>]
dinput
ouput
.
Power
amplifier
se
(optional)
speakers
Ignition
key
switch
Power supply
UD lead (Red) ®
{_} abe (To ignition)
eI Memory backup lead (Yellow)
{_} ® (To battery) = i i
Ground lead (Black) © (To car chassis) =s
Power control supply lead (Blue/White) Battery
(Full automatic Power antenna control lead)
Automatic illumination/Dimmer control
supply lead (Orenge/ White)
(To light control switch)
‘Phone interface lead (Gray)
Connect to the plus © or minus © terminal CAUTION
of the telephone speaker or buzzer, or to the
head phone jack or speaker terminals.)
+ Even with two speaker system,connect the
speakers to each connecting cord, but avoid
the connections as shown below.
ipe)
<=] © Front left
Ss speaker
(White stripe
[REAR
t
)
ee
Rear
left
a5]
O
speaker
(Gray
stripe,
®
[FRONT
-
8)
Fron
ia
crane
the
(Purple stripa
oS] 4
Re 1 © Rear right
iS) speaker
a
5
(Green str
CD — Changer
control
output
Output
Control box unit
(Provided with
the KENWOOD
CD — Changer )
KENWOOD CD — Changer
(Option)
(En) 33

KRC-851D
DISASSEMBLY
FOR
REPAIR
Replacing
the
motor
(1)
Replacing
the
pinch
roller
1.
Disconnect
the
flexible
cord...
1)
6.
Detach
the
spring...
6}
2.
Remove
the
two
screws
@
and
disconnect
the
7.
Remove
the
two
screws
@
and
detach
the
sub
chas-
board.
sis.
3.
Take
out
the
washer
@
and
detach
the
loading
arm.
8.
Detach
the
pinch
rollers
individually
...
3]
Replacing
the
sub
motor
(2)
Replacing
the
Playback
head
4.
Take
out
the
washer
€}
and
detach
the
door
arm
9.
Remove
the
two
screws
@
and
detach
the
head.
plate.
5. Remove the two screws @ and detach the motor
assy.

KRC-851D
BLOCK LEVEL DIAGRAM
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KRC-851D
CIRCUIT DESCRIPTION
SYNTHESIZER UNIT (X14-285)
Use and Function Operation and Condition
TAPE EQ amplifier
| DOLBY B/C type
1/2Vec buffer
| Power amplifier BTL Output
PLL ~ For Synthesizer Tuning
| CO-CH interface Data Buffer
8,9 | Voltage detection SV for I1C12
10 T.ADV a ' Between-tunes Detection
11 Mecha. sub moter driver
12 4 Microprocessor | Key input,PLL,LCD control
14 i AVR _ | Veo for audio,tuner
15 ACC detection ‘ For muting
Q1,2 | E€Q mute
Q3-6 | Audio mute _
Q7,8 ' LOUDNESS SW
Q9,10 | VOL.boost SW
Q11,12 Buffer ets Power amplifier input
Lo/Dx SW For AM
Q14 LPF ee For PLL
Q15,16 TUNER +B SW 7 | Q1S:FM Q16:AM
Q17 / AM BS driver
Q18 | AM AGC cut SW For AM
Q19 | SK tamp inhibit SW
Q20 | ST IND. driver
Q2) FM MUTE inverter i SEEK STOP signal
Q22,23 ; SD signal inverter | SEEK STOP signal
VCC SW for PLL LPF
Q25-28 | P-CONT.
Q31 [ DIMMER inverter
DK/RST out inverter
RST in inverter
Q34 | CD-CH DATA inhibit
| Q34,36 driver
CLK inhibit
Q37 CD-CH CONT buffer
Q38 | CD-CH REQ buffer
Q39 RESET
Q40 ; POWER ON SV SW
Q41 POWER ON SW | Active LOW
Q42,43 j; 9.6V AVR
Q44-46 | T-ADV SENS. SW ie.
Q47,48 j_AVR for SUB MOTOR _ | 10V(Kick:14v)
Q49 i KICK SW i
Q50,51 | MANUAL RESET 4
Q52,53 SK/VALET,DK SW ‘ Key matrix control
Q54,55 | DINMER SW Se
T
|
+—
|
:
+
|
|
|

KRC-851D
CIRCUIT DESCRIPTION
SYNTHESIZER UNIT (X14-285)
Use
and
Function
Operation
and
Condition
Q56-59
|
ILLUM
SW
Amber/Green
Q60,61
AVR
control
Q62
,63
AVR
for
lamp
Q64,65
|
MAIN
MOTOR
SW
ago
|
Acc
SW
|
POWER
ON
Q81
7.5V
AVR
SW
Q82
7.5V¥
AVR
=<
Q83 _|_ LOUD SW driver
Q84 _i Ripple filter
Q85 j VOL. boost SW driver
Q86 ,87 Audio mute driver
Q88 ,89 | DOLBY NR control
Q90-92 | ACC detection
iC] ‘ FRONT PREAMP
{C2 i REAR PREAMP
{c3 : Analog SW *
1C4 __tsolation amp _
{c5-7 ‘a Buffer amp
Signal selection
EXT.MUTE SW
|
FM IF amp/ DET.
FM MPX / NC
SOK ;
| Buffer amp
RESET
FM IF amp —
$0 buffer
| MPX buffer
cRSC SW
AFC SW

KRC-851D
CIRCUIT DESCRIPTION
7.5 V AVR
1C14: M5237L is the AVR IC exclusive for driver and
used in combination with the PNP transistor.
When the power is turned ON, 041 turns ON to pull
the base of Q81 to turn 081 ON.
When O81 turns ON, IC14 pulls the base of Q82
through R292.
The collector output voltage of Q82 is divided by
R292 and R293, then fed back to IC14.
IC14 compares the above voltage with the internal
reference voltage and controls the base voltage of
Q82 so that the returned voltage coincides with the
reference voltage.
C142 makes the rising edge of VCC when the power
is turned ON become gentle.
ACC Detection Circuit
IC15: PST529D-MT is used for power voltage surveilance.
ACC voltage is divided by R306 and R308, and
voltage-limited by D42, then applied to terminal |
(input) of IC15.
When the input voltage (terminal |) is dropped below
threshold voltage (approx, 8 V, when converting to
ACC voltage) of C15, terminal O (NPN, open collector)
turns ON (= low).
When terminal O if IC5 is inverted to low, the emitter
of Q90 goes low and Q91 turns OFF, then Q92 turns
OFF.
Therefore, 1C12 pin (33): ACC | which is pulled down
by R310 goes low. That is, it is judged as ACC voitage
is at low level.
At the same time, IC4, 5 pin (4) STBY (standby) pin is
inverted to low via D44, and turns PWR (power) IC
OFF, while the base of Q86 is pulled so that Audio
Muting (MUTE) is activated.
When the ACC voltage raises and the terminal | of
IC15 exceeds the threshold voltage, the operation will
be reversed and it is judged as the ACC voltage is at
high level, while the PWR (power) IC is turned ON
and Audio Mute is released.
(However, since Audio Mute is ORed with IC12 pin
(23) MUTE, audio muting will not be released immedi-
ately because of the latter MUTE, even if the above
operation releases the MUTE)
vce BACK UP +8
POWER ON
(LOW?)
GND
Vref: Internal reference voltage = 1.26 V
R309
1c 12@) Pwr
1c4,5
MUTE
Bu SV
ACC
+8
1ci2
ACCIN

CIRCUIT DESCRIPTION
VREF Buffer
IC2: CXA1332M works using the voltage which is the
half of VCC (1/2 VCC) applied to pin (17): VCTO as a
reference. That is, the 1/2 VCC is used as the signal
ground.
In this unit, since all the power supply works with a
single power, the above 1/2 VCC (VCTO) is buffered by
the voltage follower op-amp IC3 so as to supply the
power to each block.
Pin (1) output supplies 1/2 VCC to the following:
CD-CH isolated amp
AUX isolated amp
Analog switch buffer amp
Tone amp
Pin (2) output supplies 1/2 VCC to the following:
Pre-amp
Power amp input buffer
AC GND of power amp negative feedback
Main in isolated amp
Manual RST (Reset) Circuit
When the voltage at pin (7) is inverted to high, IC12 is
initialized if pin (28) is at high level.
When the voltage at pin (7) is inverted to low, IC12
stops its function, and interrupts each power circuit and
this causes shock noise.
Therefore, Audio Mute is activated by the collector
output of Q51, while 1C12 pin (7) is controlled with a
slight delay determined by the time constant of R189
and C129.
The Voltage charged in C128 is applied to 1C12 pin (28)
via D28 and R188, but the reverse current is inhibited by
D28 even when the collector of 051 goes low (Q51
turns OFF), while since discharging is done with a gentle
time constant consisting of R187 and C128, the high
level is kept for a while.
BU 5V
1¢12(7)
1cl2
sw
asi
COLLECTOR
aso
BASE
— 250
1e@= COLLECTOR
1c 12 @8)
MUTE
KRC-851D
1c 2 (7) veto
c3
TO +8(7.5V)
RST( RESET) SIGNAL
FOR CO-OH. AND
AUDIO MUTE.
028
TCl2 PIN(23) MUTE

KRC-851D
CIRCUIT DESCRIPTION
Description of EXT-MUTE
With the power ON, when the EXT-MUTE signal is ap-
plied (the signal is inverted from high to low), the
“CALL” indication appears on the 7-segment display
then, the unit enters the all-off status.
When any of the TUNER, CD or TAPE key or the MODE
key on the remote control is pressed, or when the power
of the unit connected to the PACK IN or PREOUT termi-
nals is turned ON, the corresponding function starts play-
back regardiess of whether or not the signal is turned
ON.
When the ACC is turned ON while the “CALL” indication
appears, the unit enters the Last Tuner mode.
*While 2 seconds after the EXT-MUTE signal is
sensed, any key will not be accepted.
@ EXT-MUTE during DK interruption:
The EXT-MUTE function will have priority even during
DK interruption.
@ EXT-MUTE during playing of the unit connected to
PREOUT:
If the unit connected to the PREOUT terminals is
being played, the P-CON is turned ON while 2
seconds, or until the RESET-IN is turned OFF, to reset
the subsequent unit.
If the RESET-IN is turned ON within 2 seconds after
the EXT-MUTE is sensed, the P-CON is turned ON 200
msec later so as not to turn ON the subsequent unit.
If the RESET-IN is still ON even when 2 seconds after
the EXT-MUTE is sensed, the display is changed from
“CALL” to “DA” then the previous mode of the subse-
quent unit will resume.
@ EXT-MUTE during audio adjustment:
When the EXT-MUTE is turned ON during adjusting
the BASS, TREBLE, BALANCE or FADER, the adjust-
ment mode is changed to volume adjustment mode
automatically, then the rotary encoder signals will not
be accepted for 2 seconds.
@ EXT-MUTE during inputting the VALET CODE:
During registration of the code:
The entered code will be cleared and the VALET
CODE registration mode will be released.
During inputting the VALET code to release the
VALET mode:
The EXT-MUTE signa! will be ignored.
10