Technics RS-M228X User manual

ORDER NO. ARD82050143C8-20
Service
Manual
Cassette Deck
dbx
NR,
Soft-Touch
Cassette
Deck
RS-M2
28X
Gaied iene
Black Face
DO [saavaveren]
( This is the Service Manual for the |
following areas.
D)-------+ For all European areas
except United Kingdom.
titteeens For United Kingdom.
[N] --+-- For Asia, Latin America,
Middle East and Africa
areas.
| [A] e+ seeeee For Australia. |
RS-M24 MECHANISM SERIES
Specifications
Track system: 4-track 2-channel recording and playback Outputs: LINE; output level 400 mV, output impedance
Motor:
Electrical
governor
motor
2.2kQ
or
less
Tape speed: 4 8cm/s HEADPHONES; output level 125mY (82) appli-
Wow and flutter: 0.048% (WRMS), +0.14% (DIN) | cableineaapmons Impedance Oh 72208
Frequency response: Metal tape; 20 —18,000Hz Bias frequency: 89 kHz
30 —17,000Hz (DIN) Heads: 2-head system
CrO2 tape; 20—18,000Hz 1 MX head for record/playback
30 — 17,000 Hz (DIN) 1 double-gap ferrite head for erasure
Normal tape; 20 —17,000Hz Power requirements:
30
—
16,000
Hz
(DIN)
DIN]
---
AC
110/125/220/240V,
50-60
H:
Dynamic range: 110dB (at 1kHz), dbx in B] --- AC 240 V, 50Hz
Max. input level [A] --- AC 240 V, 50-60Hz
improvement:
10dB
or
more
improved
with
dbx
in
(at
1
kHz)
ee
oe
Signal-to-noise ratio: dbx in; 92 dB ia us A0V
Dolby NR in; 67dB (above 5kHz) on,
Dolby NR out; 57 dB (signal level = max. input Power consumption:
level A weighted, CrOz type tape) DyByAl --- 20W
Fast forward and : ; N] ++ 15 W
rewind time: Approx. 90 seconds with C-60 cassette tape Dimensions: 43.0cm(W) x 10.9cm(H) x 28.0cm( D)
Inputs» MIC; sensitivity 0.25 mV, applicable microphone Weight: 5.0kg
impedance 4002 — 10kQ
LINE; sensitivity 60 mV, input impedance more
than 40kQ
Specifications are subject to change without notice.
* The term dbx is a registered trademark of dbx Inc.
+* ‘Dolby’ and the double-D symbol are trademarks of Dolby Laboratories.
Te chnics Matsushita Electric Trading Co., Ltd.
P.O. Box 288, Central Os; aka Japan

RS-M228X
CONTENTS
ITEM PAGE
LOCATION OF CONTROLS AND COMPONENTS ------------ 2
DISASSEMBLY INSTRUCTION --+----cseeers sees eeeee te teeee ee eees 3
MEASUREMENT AND ADJUSTMENT METHODS
(without dbx SYSTEM) ‘ibietalerbisiaiolelala'e einitie slorw-sjateisiels ewwle eerie viele lois 5
MEASUREMENT AND ADJUSTMENT METHODS
(for dbx SYSTEM) (gE ut saiate Syste ySejeie bie ware dig 915 olan Cat sigleieretelg bate ever 11
* TROUBLESHOOTING CHART FOR dbx SYSTEM ---- 11
* ADJUSTMENT PARTS LOCATION OF dbx
SYSTEM feesccceston stoves nnd Sia teowetnn reduce tet ee teenasiy se 13
* BLOCK DIAGRAM OF dbx SECTION ------+--eeeeeeeee ee 13
* dbx SYSTEM CHECKING METHOD ..---------------e-5+ 5 14
¢ ADJUSTMENT OF dbx SYSTEM --vecececececeeeeeeeeee ees 15
* CHECKING PROCEDURE FOR PROBLEMS -.---------- 16
-
ELECTRICAL
PARTS
LOCATION
-:-:::ceccececeeeeeeteeeeeeneees
18
BLOCK:
DIAGRAM
2-:
seeds
eseeonseseocue
ttesseiag
sence
ecesce
vat
eecoess
20
ITEM PAGE
SCHEMATIC DIAGRAM
(MAIN/POWER SUPPLY SECTION) ----:++seereeeeeeeees 22
CIRCUIT BOARDS
(MAIN/POWER SUPPLY CIRCUIT BOARD) ----+----- 25
SCHEMATIC DIAGRA
(dbx SECTION) ---:-e:ceceseecee eee eeeeteeeeeeenteeneeeseereeeees 29
SCHEMATIC DIAGRAM
(FL METER SECTION) --c-eecceeeeece eet eceeseeeeeeeea seen eres 30
CIRCUIT BOARDS
(dbx/FL METER CIRCUIT BOARD) ----:++-esreerrereees 31
WIRING CONNECTION DIAGRAM .--eeeeeeeeeeeeeeeeneeer tenes 33
CABINET PARTS LOCATION <0: -e:-sseececeeeeee teste eeeereeeaees 35
MECHANICAL PARTS LOCATION -evcececcecececeteeeteeeeenee 37
MOTOR UNIT DISASSEMBLY ------:ereeceeteereeet eee eeteeea ees 40
PRECAUTIONS FOR MECHANISM UNIT ASSEMBLY ---- 40
LOCATION OF CONTROLS AND COMPONENTS
Headphones Jack (phones)
Power Switch [power (push on)}]
Eject Button (eject)
Cassette Holder
Tape Counter (tape counter)
Recording Indicator (rec)
Tape Indicator
[Auto Tape Select (NormaleCrOzeMetal)]
FL (fluorescent level) Meter
Input Level Controls
[input level (L-®-R)]
Noise Reduction Select Switch
[Noise Reduction (Dolby NR**eout
dbx] tapee (dbx| disc)]
Fast Forward/Cue Button
[ff/cue (>> )]
Rewind/
Review Button
{rew/rev ( ¢4)]
i}
i)
1
t
i}
1
Counter Reset Button i
(counter
reset)
|
Input
Select
Button
i}
i]
i}
I
i}
!
!
i
¢
[input select ( @linee = mic)]
Microphone Jacks [mic (left@right)]
Record-Muting Button [rec mute (0))
Output Level Control (output level)
(ea he Power Voltage Selector
[DIN] ...* For all European
areas except United Kingdom,
Asia, Latin America, Middle
East and Africa areas.
0
Record Button
{rec- 9 (O)]
Play Button
(play- G(P))
Pause Button
[pause (1)]
Stop Button
[stop (@)]
;
Line Output Jacks (LINE OUT (LeR)]
Line Input Jacks [LINE IN (Le@R)]
—> 2 =—

DISASSEMBLY INSTRUCTION
{
* The head azimuth can be
adjusted by removing the
cassette lid.
Fig. 1
Power supply
Owe (7)
circuit board
Fig. 5
i
Recording-4
(O)
.2(R),— (T) dbx
eet circuit
Se >} board
RS-M228X
(F)
Fig. 4
FL meter unit
(N) Pull out
T
RS-M228X
Fig. 7
Procedure
To remove ——.
Shown in fig. ——.
Case cover
¢ 4 screws
Bottom cover
Front panel
6 screws
Input volume knob-l. assembly ---
Input volume knob-R assembly
1 screw
3 screws
Power supply circuit board
Pull out the connector
28
Cord clamper
Pull out the connection rod (2)
8 red screws
FL meter unit
Pull out the connector
Pull out the FL. meter uni
dbx circuit board
2 red screws and washers
Pull out the dbx circuit board
132—->3-5-6-7
Main circuit board
Cord clamper
Recording wire
Pull out the connector
Pull out 6 connectors
Al, [B
1 ,
7 red screws
1>2>3-+5 8
Mechanism unit
¢ Pull out the counter reset
¢ 4 red screws
¢ Pull out 6 connectors
Al, (Bl, [€
, ’
13 2-35-89
Cassette holder
¢ Cassette {i
* Slide ind

RS-M228X
MEASUREMENT AND ADJUSTMENT METHODS
Tape
selector
(Tape
mode
switching)
(without
dbx
SYSTEM)
For measurement adjustment with test tapes without tape detection
holes switch tape modes as follows.
(For normal tape mode, just insert a normal tape into the cassette
holder.)
: Connection
* Metal tape mode setting: wire
Metal tape mode is obtained by disconnecting the 3 pin socket
from the 3 pin post [B] on the P.C.B. (Printed Circuit Board).
* CrO2 tape mode setting: GROUND
First, disconnect the 3 pin socket [D] in the same way as above.
Then, as illustrated in the figure right, connect the terminal-3 of
the 3 pin post to the ground with a connection wire.
es]
3 pin post-D)
Main P.C.B.
Tape Speed
Adjustment VR VR9 VR6 VR5 VR1 VR2
VR10
ey
elk
/ pee oe
| \
, VR301
a ea ee
a aoe ae
TP5.. >, TP3. “Jumper , TP301
8
A53f
|}
Ra7é
|)
|
x
9R330
‘SL
BEAK
RESET
TERMINAL
\
Fig. 1
NOTES: Keep good condition, set switches and controls in the following positions, unless otherwise specified
@ Make sure heads are clean. @ Input selector: Line
@ Make sure capstan and pressure roller are clean. ® Input level controls: Maximum
@ Judgeable room temperature: 20+5°C (68+9°F) © Output level control: Maximum
@ NR switch: OUT
Screw (A}
® Head position (The head adjusting plate 1s provided to adjust the tape Head Adjusting Plate
adjustment
touch
of
the
head
in
cue
or
review
mode.)
Capstan
Condition 1 Press the playback button and pause button — is
* Playback and pause mode 2 Measure the space between the pressure roller and the Rk
capstan
Standard value: 0.5+0.3mm
Space (adjustable?
If the measured value is not within the standard value,
untighten screw (A), and slide the head adjusting plate
in the direction of arrow (B) for adjustment
Fig. 2
© Head azimuth L-CH/R-CH output balance adjustment a ouT
adjustment 1. Make connections as shown in fig. 3. fossratplavacic est
Condition:
* Playback mode
Playback mode VTIVM Oscilloscope
Fig. 3
i Pressure Roller
ITEM MEASUREMENT & ADJUSTMENT
Equipment 2. Playback the 8kHz signa! from the test tape Record/playback head
*VTVM * Oscilloscope (QZZCFM)
* Test tape (azimuth) Adjust screw (B) in fig. 4 for maximum output L-CH \
+++ QZZCFM and R-CH levels
When the output levels of L-CH and R-CH are not at Screw (B)
maximum at the same time, readjust as follows Fig. 4
3. Turn the screw shown in fig 4 to find angles A and C
(points where peak output levels for left and right channels L-CH peak level
R-CH peak level
are obtained). Then. locate the angle B between angles A
r
and C. .e. a paint where L-CH and R-CH output levels sudan
come together at maximum. (Refer to figs. 4 and 5.) LEVEL
L-CH/R-CH phase adjustment
4. Make connections as shown in fig. 6.
5.
Playback
the
8kHz
signal
from
the
test
tape
(QZZCFM)
—_—
aE?
Adjust
screw
(B)
shown
in
fig.
3
so
that
pointers
of
the
two
A
BC
VTVMs
swing
to
maximum
and
a
waveform
as
illustrated
in
Fig.
5
fig. 6 Is obtained on the oscilloscope
Record/
VIVM
Oscilloscope
playback
head
)VIVM
|
ra
LH
ROS
A
=e
-
revs!) .
1 Eccapee seca Fig. 7
Playback LINE OUT Vertical Horizontal Fig, &
@ Tape speed Tape speed accuracy
Condition 1. Test equipment connection is shown in fig. 8.
+
Playback
mode
2.
Playback
test
tape
(QZZCWAT
3.000H2),
and
supply
Record/playback
head
LINE
OUT
«
Normal
tape
mode
playback
signal
to
frequency
counter
ee
eae
4
Equipment 3. Take measurement at middle section of tape | | oo
4. Measure this frequency. Test tape Playback mode ay Clectric counter
* Digital electronic counter
+ Test tape --- QZZCWAT 5. ha of 3,000HZz, determine value by following Fig. 8
f — 3.000
Af d ae eS 9
ape speed accuracy 3000 * 100 (%)
where, f = measured value
Standard value: +1.5% |
Adjustment method
1. Playback the test tape (middie)
2. Adjust so that frequency becomes 3,000 Hz
3. Tape speed adjustment VR shown in fig. 1
Tape speed fluctuation
Make
measurements
in
same
manner
as
above
(beginning,
middle
and
end
of
tape),
and
determine
the
difference
between
maximum
and
minimum
values
and
calculate
as
follows:
f: —fe
Tape speed fluctuation = ——--— > Y
ape speed fluctuation 3000 * 100 (%)
f: = maximum value, f> = minimum value
Standard value: Less than 1.0%
®
Playback
frequency
Measurement
Playback
frequency
response
chart
response
1.
Test
equipment
connection
is
shown
in
Condition: fig. 3.
*
Playback
mode
2.
Place
UNIT
into
playback
mode
Aer
*
Normal
tape
mode
3.
Playback
the
frequency
response
test
tape
a6
* Output level control «-» MAX (QZZCFM). te
Equipment: 4. Measure output level at 315Hz. 125kHz, | ~2%8 rt
*VTVM — * Oscilloscope BkHz, 4kHz, 1kHz, 250Hz, 125Hz and | ~S8C
+ Test tape --- QZZCFM 63Hz and compare each output level with a - =n
the standard frequency 315Hz, at LINE (io.
OUT.
Fig. 9

RS-M228X
ITEM MEASUREMENT & ADJUSTMENT
5. Make measurement for both channels.
6. Make sure that the measured value is within the range specified in the frequency response chart
(fig. 9).
Playback frequency response adjustment
1. Open or short the circuit's connection points to adjust playback frequency response (see fig. 10).
2. The frequency response when connection points (a) (L-CH) and (a’) (R-CH) are shorted/open
changes as short/open condition at connection points changes as described below (table 1).
Short/open conditions, in turn, differ with sets due to the differences in fine adjustments made prior to
shipping. If readjustments are required, set conditions so that results are as close to the standard
value as possible.
Connection point
(a) (L-CH), (a') (R-CH)
6 kHz 8kHz 10 kHz 12.5kHz
around around around around
Short
+0.2dB}
+04dB)
+08dB)
+12dB
around around around around
ope -~0.2dB] -04dB| —08dB) —1.2dB
Table 1
Connection.“
point (a') /
C7
%390P_ Connection
Record/ point (a)
Playback Head
Connection
point (a)
L-GH)
@ Playback gain _ Test equipment connection is shown in fig. 3.
Condition: . Playback standard recording level portion on test tape (QZZCFM 315 Hz, OdB), and using VTVM
measure the output level at LINE OUT jack.
* Playback mode
Ge, . Make measurement for both channels
* Normal tape mode
Equipment: Standard value: 0.4V+1¢dB
SVM. «« Oselloseope (around 0.42V: at test points TP3 (L-CH) and TP4(R-CH
*
Test
tape
---
QZZCFM
a
:
P
3
ane
a(R
E
i
Adjustment
1. If measured value is not within standard, adjust VR1 (L-CH), VR2 (R-CH) (shown in fig. 1)
2. After adjustment. check “Playback frequency response” again

RS-M228X
ITEM
MEASUREMENT
&
ADJUSTMENT
@ Erase current 1. Test equipment connection is shown in fig. 11.
Condition:
2.
Place
UNIT
into
metal
tape
mode.
Evaga‘head
* Record mode 3. Press the record and pause buttons.
+
Metal
tape
mode
4.
Read
voltage
on
VTVM
and
calculate
erase
current
by
ane
—
Eau
t
following
formula:
Record
mode
aaos
aaIPnEN
Voltage
across
both
ends
of
R125
rare
soya
a
*VTVM
*
Oscilloscope
Erase
current
(A)
=
oo
we
1 (Q) VTIVM Oscilloscope
Standard
value:
155+15mA
(Metal
position)
|
Fig.
11
5. If measured value is not within standard, adjust as follows.
Adjustment
1. Short the points (b) and (c) on the main circuit {
board diagram (see page 25)
2. Make measurement for erase current.
3.
Make
sure
that
the
measured
value
is
within
the
|
:
'
erase
current
of
140mA
to
170mA
oe
|
Open
j
—2dB
|
—1dB
4.
If
measured
value
is
not
within
standard,
short
or
point
(c
;
open
connection
points
(b)
and
(c)
for
adjustment
|
Se
0.108
O08
(see
table
2).
Table
2
_ around 70mA (Normal position)
Reference ‘valle: around 95mA (CrQ2 position)
= 1
Connection point (b) |
Open Short
© Overall frequency Note: | Overall frequency response chart (Normal)
response
Before
measuring
and
adjusting,
make
sure
:
7
Condition:
of
the
playback
frequency
response
(For
*
Record
/playback
mode
the
method
of
measurement,
please
refer
ee
*
Normal
tape
mode
to
the
playback
frequency
response)
a
*
CrO>
tape
mode
Overall
frequency
response
adjustment
ee
*
Metal
tape
mode
by
recording
bias
current
—
408
*
Input
level
controls
---
MAX
s
no
ee
*
Cute
level
control
---
MAX
ieeusdingsequanagnle
wed)
nh
al
eae
ee
Equipments
1.
Make
connections
as
shown
in
fig.
13.
i
QDH2700He
4KHE
5
KHz
|
*v1VM
+
AF
oscillator
2.
Place
UNIT
into
normal
tape
mode
and
Fig.
12
mail
*
Oscilloscope
load
the
test
tape
(QZZCRA).
.
*
Resistor
(6002)
3.
input
a
1kHz,
~24
dB
signal
through
* Test tape LINE IN
(reference blank tape)
Place the set in record mode VR9(L-CH)
- QZZCRA for Norm! 4. Fine adjust the attenuator to obtain Rama dinveack {vanDeRc Pa
* QZZCRX for CrOs 0.4V LINE OUT output head = TART "AP oseilstor
*
QZZCRZ
for
Metal
*
Make
sure
that
the
input
signal
level
33
is —24+4d8 with 0.4V output TPL{L-CH) Piayback7
voltage.
aca
secede
FA
@)
5
Adjust
the
attenuator
to
reduce
the
input
mem
NY
°6)
ro
FLA
a
ering
VIVM_Oseiloscope
6.
Adjust
the
AF
oscillator
to
generate
50
Hz,
oo}
to
100
Hz,
200Hz,
500
Hz,
1kHz,
4kHz,
VTVM
Oscilloscope
For
overall
frequency
;
; ———— response measuremen
8kHz
and
10kHz
signals,
and
record
Far
bag
cuvent
these
signals
on
the
test
tape.
measurement.
7. Playback the signals recorded in step 6, Fig. 13
and check if the frequency response curve
is within the limits shown in the overall
frequency response chart for normal tapes
(tig. 12).
(If the curve is within the charted specifications, proceed to steps 8, 9, 10 and 11,)
If the curve is not within the charted specifications, adjust as follows;

RS-M228X RS-M228X
Adjustment @: Adjustment ®: @ Fluorescent meter . Make connections as.shown (See fig. 17).
When the curve exceeds the overall frequency When the curve falls below the overall frequency Condition: 2. Connect a wire between TP301 and peak reset
response chart specifications (fig. 12) as shown response chart specitications (fig. 12) as shown * Record mode terminal (See fig. 18).
in fig. 14. in fig. 15. * Input level controls --» MAX . In the recording pause mode, apply 1 kHz
+ Output level control --» MAX (—24dB) to LINE IN.
eat _ Adjust ATT so that output level at LINE OUT
Equipment: is O.4V
* VTVM * AF oscillator
«ATT —40dB adjustment
5. Adjust ATT so that the level adjusted at step
4 is reuced by 40dB.
6. At this time, check that — 40 dB indicator is
kHz
2kHz
Wars
SSE
10
kHz
ax
So
10kHZ
lighted
halfway
(intermediate
brightness
3kHz/ /6kH
aki SikHz 71 ‘AC Hi / feu kare between full brightness and light-out: See fig.
19).
Fig. 14 Fig. 15 7. \f the indicator is not lighted halfway as
1)
Increase
bias
current
by
turning
VR9
(L-CH)
1)
Reduce
bias
current
by
turning
VR9
(L-CH))
described
in
step
6,
adjust
VR301.
and VR1G (R-CH). and VR10 (R-CH). OdB adjustment
See fig. 1 on page 5.) 2) Repeat steps 6 and 7 to confirm. i :
2) Repeat steps 6 and 7 to confirm. (Proceed to steps 8, 9, 10 and 11 if the 8 ete ae 4 (set LINE
Proceed to steps 8, 9, 10 and 11 if the curve iS now within the charted specifica- Rion a EN ot lots . . : ;
curve is now within the charted specifica- tions.in fig. 12) . time, ee oe le is lighted halfway (intermediate brightness between full
tions is fig. 12.) 3) If the curve still falls below the charted i iaprone: edie yeaa ig. 20).
if th till h ificati ificati i i : ;
3) e curve still exceeds the specifications specifications (fig. 12), reduce bias current ” Repent adyistmien|e: and chiaciealestene 4 G26: 78) S anal 0 tae Ge tarde tines
fig. 12), i bi t further and furth t re ; ; ,
ee
7
on
aey
aie
Dive
aee
Letras
iene
Disconnect
the
wire
between
TP301
and
ground
terminal,
which
had
been
connected
at
step
2
. Place UNIT into CrO2 tape mode.
ee,
Been
Borne
A
Overall
frequency
response
chart
(CrO2,
Metal)
©
Dolby
NR
circuit
1.
Test
equipment
connection
is
shown
in
fig.
21.
jezdcny
|
Tralee
es
4kH e
kH
ions
a
1D
a
TO
Condition
2. Place
UNIT
into
record mode,
set
the
Dolby
NR
switch
|1C3(R-CH)
2, 2 OINEIES 2 ANG) 9 Bitz HT | Pe a scardaned to OUT position and supply to LINE IN to obtain a
signals.
Then,
playback
the
signals
and
Foner
adie
oa
—34.5¢B
at
PIN
@
[IC2
(L-CH).
C3
(R-CH)]
check
if
the
curve
is
within
the
limits
asi
Z|
‘
aerate
Sie
ie
ae
(frequency
5
kHz}
-
.
shown in the overall frequency response * Input level controls --- f Bak The val IN :
: : t +2.5)dB
chart for CrO2 tapes (fig. 16). it Yt TU Equipment: COON! Weel eee IN Dostonse | ial
Hi aunt greater than the value at OUT position of Dolby NR e
. Place UNIT into metal tape mode change HH or ee ad Ht * VTVM * AF oscillator awiten 5°
test
tape
to
QZZCRZ,
and
record
50Hz,
fligots
$300
Hz
hy
xu
ate
Tt
N72
Sie
*
ATT
*
Oscilloscope
:
100Hz, 200Hz, 500Hz, 1kHz, 4 kHz, uy fa ae \\\g20H| 4kHz NE Rte * Resistor (600 2) Fig. 21 Genin
8kHz, 10kHz and 12.5kHz signals 400 Hz 600 Hz 700 Hz \ §kHz 7kHz
Then, playback the signals and - Fig. 16
check if the curve is within the limits :
shown in the overall frequency response chart for metal tapes (fig. 16).
. Confirm that bias currents are approximately as follows when the UNIT is set at different tape mode.
* Read voltage on VTVM and calculate bias current by following formula:
Value read on VTVM (V)
10 (Q)
Connection
AF
oscillator
ATT
Record
ii
Bias current (A)
Standard value:
around 340 uA (Normal position)
around 440 ZA (CrO2 position) : measured at TP1(L-CH) and TP2 (R-CH)
around 710A (Metal position)
@ Overall gain Test equipment connection is shown in fig. 17.
Condition: 2. Place UNIT into normal tape mode, and load the test Record /playback
* Record/playback mode tape (QZZCRA).
+ Normal tape mode _ Place UNIT into record mode.
* Input level controls --» MAX . Supply 1kHz signa! (—24 dB) from AF oscillator. 2 as
*
Output
level
control
---
MAX
through
ATT
to
LINE
IN.
AF
oscillator
A
Lune
in
Record
mode
* Standard input level; . Adjust ATT until monitor level at LINE OUT becomes
MIC «+++ —72+3¢dB OAV.
LINE IN--» —24+3dB _ Playback recorded tape, and make sure the value at
LINE OUT on VTVM becomes 0.4 V.
_ (f measured value is not 0.4V, adjust VR5 (L-CH),
VR6 (R-CH). Test tape
. Repeat from step (2)
Test tape
Playback head LINE OUT
Equipment:
* VTVM * AF oscillator
* ATT * Oscilloscope
* Resistor (600 2)
+ Test tape
(reference blank tape)
--QZZCRA for Normal
Playback mode “yrym
Oscilloscope
Fig. 17

RS-M228X
MEASUREMENT AND ADJUSTMENT METHODS For dbx SYSTEM)
START
@ Check for
expansion
© Check the voltage at individual
sections of the regulated power supply
circuit in dbx circuit
e Adjustment of regulated power
supply circuit in dbx circuit
@ Repair the power supply circuit section
@ Check for ree ey
expansion
© Check for
standard level of dbx
@ Adjustment of dbx standard level
Repair the control circuit section control
@ Check for
expansion
check of INPUT BAND >>
ASS FILTER (27H2—20kH2)
_Ghack of RMS
FILTER (27H2—10kHz)
_ [ONPAGE13] |
@ Check for
expansion
@ Check the frequency
tesponse of the dbx circuit
TROUBLESHOOTING CHART FOR dbx SYSTEM
Fig. 1
Check the constants of the INPUT
BAND PASS FILTER elements
Check the operation of transistors |
203 and 0204 4
Check the constants of the BAND
PASS FILTER elements
Check the operation of transistors
0221 and 0222
¢ TROUBLESHOOTING CHART FOR dbx SYSTEM
The troubleshooting chart for the dbx system is shown in Fig. 1.
Please follow the sequence of this chart for checking and
repairing the dbx system.
The figures shown in each block indicate the page on which
the checking method, adjustment or measurement is explamed.
Repair the INPUT BAND PASS
Repair the RMS FILTER section
Check the voltages and signal wave
forms at individual sections of the
RMS detector
1
Repair the RMS detector section
Check the voltages at individual
sections of the VCA circuit. Check
the constants of the Pre-emphasis/
De-emphasis circuit elements.
Repair the VCA circuit section or
Pre-emphasis/De-emphasis circuit
Output signal distortion factor
adjustment

RS-M228X
¢ ADJUSTMENT PARTS LOCATION OF dbx SYSTEM
VR204 VR206
(320
1
\ Lo
TP206
f eae
R2508 |;
/
a a
TP204
240
NS
» ae
\
ee
id
., TP207 ~
Tbreos
\
cs
\
press
‘
{press
VR203 VR205
TP205 >,
a apl \
* Pyreas
X nae
cen
7 TP203 ~TP201
Fig. 2
BLOCK DIAGRAM OF dbx
SECTION (L-CH ONLY)
{@P) NIVOWOA
20 wo 500 th Sr 10k 2OKM:
[PRE EMPAHSIS CHARACTARISTIC]
20 100 «500 tk Bh 10k 2OmHe
B00 O
{DE- EMPHASIS CHARACTARISTIC}
100
CONTROL VOLTAGE (mV)
[VCA CHARACTARISTIC]
300 SOO tk Se 10n 20Kne
(BAND PASS FILTER CHARACTARISTIC]
DISe. MODE (DECODE: S1; disc position)
dbx CIRCUIT BOARD
VR201
VCA Symmetry
adjustment VR
Q203
INPUT BAND
PASS FILTER
(27 Hz—20 kHz]
VCA
1€201, 205
L-CH
output
DE EMPHASIS
VR203
RMS detector
adjustment VR
1203
RMS
DETECTOR
VR207
dbx standard level
adjustment VR (Decode)
1C205 Q221
RMS FILTER
(27 Hz—10 kHz)
Q201, 207, 209, 217, 219
205, 213, 215, 211
CONTROL CIRCUIT
Q13, 14, 15, 16
CONTROL CIRCUIT From. St
(NR select switch)
bey
test
‘Tt
HI
2 00 «S00 hk ‘Bk 10K 2OKH2
[RMS WEIGHTING CHARACTARISTIC]
bie
ne mi
=50—40- 30-20-10 0+10+ 20430440450
RMS DETECTOR INPUT LEVEL (dB)
[RMS DETECTOR CHARACTARISTIC]
L 1
20 00 500 tk Ge Ok 2OKHz
IRMS FILTER CHARACTARISTIC]
Note: Encode/decode selection of the dbx circuit in RS-M228X
is done with a control circuit, composed of transistors.
(This control circuit is interlocked with S2 (NR selection
switch).) 13
T T T q T 7 qT [ENCODE OUTPUT CHARACTARISTIC]
te ate
est ttHttte st + Set f
st oetit+ 4444 a a
t +4 CONTROL VOLTAGE (mv)
of itt Hatt |
93 iat Hi (VCA CHARACTARISTIC]
atte + +e
“Trt
3s 10s 20KH2 Cit Lum
20 wo $00 Sex 10k 2OKHE
{BAND PASS FILTER CHARACTARISTIC]
ENCODE MODE\ (RECORD MODE: S1: dbx tape position)
VCA Symmetry
adjustment VR
PRE
EMPHASIS
VR203
RMS detector
adjustment VR
Q203
LOW CUT
FILTER
VR205
dbx standard level
adjustment VR
O1P205|
TP207
1C203
RMS DETECTOR
RMS
WEIGHTING
1C205, Q221
RMS FILTER
Q201, 207, 209, 217
219, 213, 215, 211
CONTROL CIRCUIT
Q13, 14, 15, 16
CONTROL CIRCUIT
From S1
(NR select switch)
+300}
+240]
+180
+120
+60
~60
-120
—180
~ 240
300} -
=50=-40-30-20-1O HO+430440+50
AMS DETECCAR input tevel (dB)
{RMS DETECTORG HARACTARISTIC]
20 7007 BOQ Sm TOK Oks
[RMS WEIGHTING CHARACTARISTIC}
i i
Sk 1k 2OW2
{RMS BAND PASS FILTER CHARACTARISTICI
Fig. 3

RS-M228X
dbx SYSTEM CHECKING METHOD
NOTES: Keep good condition, set switches and controls in the following positions. unless otherwise specified.
@ Input level controls: Maximum
ITEM CHECKING METHOD
@ Check for expansion
Condition:
* Stop mode
* Input level controls --- MAX
* Output level control --- MAX
* Noise reduction selector
--- disc/dbx tape
Equipment:
* VTVM * AF oscillator
* ATT * Oscilloscope
* Resistor (600 22)
® Check for standard
level of dbx
Condition
* Stop/record mode
* Input level controls --- MAX
+ Noise reduction selector
++ disc/dbx tape
Equipment:
* VTVM * AF oscillator
* ATT * Oscilloscope
* Resistor (600)
@ Check the frequency
response of the dbx
circuit
Condition
* Stop/record mode
* Input level controls --- MAX
* Noise reduction selector
-+- disc/dbx tape
Equipment:
* VTVM * AF oscillator
* ATT * Oscilloscope
* Resistor (600)
© Output level control: Maximum
® Check for expansion
1. Make the connections as shown in fig. 4 and
apply 1kHz ~ 27dB signal from LINE IN.
and set the noise reduction selector to disc
LINE IN
LINE OUT
[—*
position
AF
oscillator
Adjust ATT, increase input signal level by 10 dB.
and make sure that the reading for VTVM
increases by 20dB+1dB
ATT ¢
6002
Resistor
i :
Stop/record mode yTVM Oscilloscope
Fig. 4
Adjust ATT, decrease the input signal level. and make sure that the reading for VTVM decreases by
20dB+1dB
@®-1 Check for standard level of dbx in dbx Encode mode
1. Make the connections as shown in fig. 5 and
apply 1kHz —274dB signal from LINE IN.
and set the noise reduction selector to dbx
ape position
2. Set the unit to record mode. adjust At T so
that the signal level at TP201 (L-CH) and
TP202 (R-CH) is 300 mV
3. Make sure that the signal level at TP203 (L-CH)
and TP204 (R-CH) is 300mV+0.5dB
AF oscillator
TP201 (L-CH)
VTVM_ Oscilloscope
TP203(L-CH) |=
TP204(R-CH)}! _/
TP202(R-CH) ©
ATT
600
@-2 Check for standard level of dbx in dbx Decode mode
1. Make the connections as shown in fig. 5 and apply 1 kHz —27dB signal from LINE IN. and check as
follows:
TP207-4..[
Record mode
Resistor
LINE IN
dbx circuit board
Fig. 5
2. Set the noise reduction selector to disc position and adjust ATT so that the signal level at TP201
(L-CH) and TP202 (R-CH) becomes 300 mV
3. Make sure that the signal level at TP203 (L-CH) and TP204 (R-CH) is 300mV+0.5dB
@-1 Check the frequency response during decoding
1. Make the connections as shown in fig. 5 and apply 1 kHz
— 27 dB signal from LINE IN, and check as follows:
2. Set the noise reduction selector to disc position, and adjust
ATT so that te signal level at TP201 (L-CH) and TP202
(R-CH) becomes 300 mV.
3. With the signal level at TP203 (L-CH) and TP204 (R-CH)
as OdB. change the signal frequency to 1OOHz, 20Hz and
7 kHz respectively. Read signal levels at TP203 (L-CH)
and TP204 (R-CH) and check that they are within the
specifications-1
@-2 Check the frequency response during encoding
1. Make the connections as shown in fig. 5 and apply 1 kHz
— 27dB signal from LINE IN. and check as follows:
2. Set the noise reduction selector to dbx tape position. and
the unit to record mode
3. Adjust ATT so that the signal level at TP201 (L-CH) and
TP202 (R-CH) is 300 mV :
4. With the signal level at TP203 (L-CH) and TP204 (R-CH)
as OdB, change the signal frequency to 1OQHz and 7 kHz
respectively. Read signal levels at TP203 (L-CH) and
TP204 (R-CH) and check that they are within the
specitications- 2.
Specifications-1
| Frequency
Signal levels at
TP2023 and TP204
1 kHz
0.dB (300 mV)
100
Hz —0.5dB* 1dB
20Hz
—30dB+5dB
7 kHz
+7dB+1dB
Specifications-2
Frequency
Signa! levels at
TP203 and TP204
1k Z 0 dB (300 mV)
100
Hz +0.5dB+1dB
7k
z ~ 3.5dB+1dB
NOTES:
e If the results of the above checks @. © and @ do not satisty the specifications, perform the following adjustments
If the specifications are not satisfied even after the adjustments, follow the checking procedure for problems.
¢ lf the output signal is not produced or is extremely distorted, follow the checking procedure for problems