Sony ST-88 User manual

Fm Tuner Section
Tuning range:
Antenna:
Intermediate frequency:
Usable sensitivity:
S/N ratio:
Capture ratio:
Selectivity:
Image rejection:
Spurious rejection:
A-m suppression:
Frequency response:
Harmonic distortion:
Fm Stereo separation:
A-m Tuner Section
Tuning range:
Antenna:
*. STEREO TUNEN $T-80
Lf enn,
SPECIFICATIONS
87.5 to 108 MHz
300 ohms balanced
10.7 MHz
2.2 LV (IHF)
1.7 LV (S/N = 30 dB)
65 dB
2.5 dB
50 dB (IHF)
45 dB
75 dB
45 dB
30 Hz to 15 kHz +2 dB
Mono; 0.5 % at 400 Hz 100 % Mod.
Stereo; 0.8 % at 400 Hz 100 % Mod.
greater than 36 dB at 400 Hz
530 to 1,605 kHz
Built-in bar antenna with external
antenna provision
Intermediate frequency:
Sensitivity:
19 kHz, 38 kHz suppression:
S/N ratio:
Image rejection:
\-f rejection:
Harmonic distortion:
General
Power requirements:
Power consumption:
Dimensions:
Net weight:
Shipping weight:
AEP,
UK and USA Model
FM STEREO/
FM-AM TUNER
455 kHz (USA and AEP Model)
468 kHz (UK Model)
48 dB/m, built-in antenna
100 LV, external antenna
45 dB
50 dB
40 dB at 1,000 kHz
45 dB at 1,400 kHz
30 dB at 1,000 kHz
0.8 %
120 V, 60 Hz ac (USA Model)
110, 127, 220, 240 V 50/60 Hz ac
(AEP and UK Model)
10W
128 (w) x 232 (h) x 210 (d) mm
516 (w) x 94g (h) x 8% (d) inches
approx. 2.7 kg (5 Ib 15 oz)
approx. 3.2 kg (7 Ib 1 oz)
SONY.
SERVICE MANUAL
pte

Section
TABLE OF CONTENTS
Title
Page
TECHNICAL
DESCRIPTION
1-1.
Block
Diagram
2...
2
ee
eee
\
DISASSEMBLY
AND
REPLACEMENT
2-1.
Wooden
Case
Removal...
2-2
eee
eet
ets
2
9-2.
Front
Panel
Removal...
2...
eee
ee
ere
ts
2
9-3.
Front
Subchassis
Removal...
2.
eee
eee
ts
2
2-4.
Fm
(A-m)
Front-End/I-f
Amp/MPX
and
Preamplifier
Board
Removal...
.-
ee
eee
ett
te
3
7-5.
Power
Supply
Board
Removal
....--
eee
setts
3
9.6.
Dial
Cord
Restringing
©...
eee
et
3
9-7.
DialLamp
Replacement
...-.
0
eee
rete
ttre
4
2-8.
Tuner
Input
Meter
Replacement...
--
+--+
eee
eet
tt
4
2-9,
Band,
Mode,
Afc
and
Power
Switch
Replacement
...--
+--+
--:
4
9-10.
Chassis
Layout...
2.
ee
ee
5
ALIGNMENT
AND
ADJUSTMENT
3-1.
Fm
I-f
and
Discriminator
Alignment
....-
+--+
eee
rrrrcs
6
3-2.
Fm
Frequency
Coverage
and
Tracking
Alignment
.....----:5
7
3-3.
Fm
Stereo
Separation
Adjustment...
6.
-
eee
te
tts
8
3-4,
A-mI-f
Strip
Alignment
..
2...
-
ee
ee
ree
ts
9
3-5.
A-m
Frequency
Coverage
and
Tracking
Alignment
.....--+---
9
REPACKING......--
+++
ee e5
ee
en
ee
11
DIAGRAMS
5-1.
Mounting
Diagram
—
Power
Supply
and
Attenuator
Boards
.....
-
13
5-2.
Mounting
Diagram
—
Fm
(A-m)
Front-End/I-f
Amp/MPX
and
Preamplifier
Board...
.-
+--+
eee
rrr
tts
14
5-3,
SchematicDiagram....----
eee
eee
ett
15
EXPLODED
VIEWS...
...----
0s
etree
teers
17
ELECTRICAL
PARTS
LIST
.....---
22s
ee
errr
19
(Ooty

SECTION 1
TECHNICAL DESCRIPTION
BLOCK DIAGRAM
1-1.
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SECTION 2
DISASSEMBLY AND REPLACEMENT
Note: All screws in this service manual are
Phillips type (cross recess), unless other-
wise specified.
(—): slotted head
2-1. WOODEN CASE REMOVAL
1. Remove the four screws (P 4 x 16) securing the
wooden case to the chassis along with the rubber
feet.
2. Remove the two screws as shown in Fig. 2-1.
mee ANT ; |
au GRouaD [Ts00s B . Fj
ey ok . ) : :
Be x8 |
~
sy
Fig. 2-1. Wooden case removal ; ae D hee ie a
j y ~
| ats
2-2. FRONT PANEL REMOVAL
1. Remove the wooden case as described in Procedure
2-1.
2. Pull out the tuning knob.
3. Remove the four screws securing the front panel
to the chassis as shown in Fig. 2-2.
4. Remove the front panel in the arrow direction
shown in Fig. 2-3.
5. Unsolder the two lead wires from the TUNER
INPUT meter and pull out the lamp socket from
the TUNER INPUT meter bracket as shown in
Fig. 2-3.
2-3. FRONT SUBCHASSIS REMOVAL
1. Remove the wooden case and the front panel as
described in Procedures 2-1 and 2-2.
2. Remove the nine screws ( (A) ) as shown in Fig. 2-4
and Fig. 2-5.
3. Pull off the STEREO lamp from the grommet. ; Fig. 2-4. Front subchassis removal
oo

«oy
Fig.
2-5.
Front
subchassis
removal
(2)
2-4.
FM
(A-M)
FRONT-END/I-F
AMP/MPX
AND
PREAMPLIFIER
BOARD
REMOVAL
1.
Remove
the
wooden
case
as
described
in
Procedure
2-1.
2.
Unsolder
the
ribbon
antenna
at
the
fm
(a-m)
front-
end/i-f
amp/MPX
and
preamplifier
board
as
shown
in
Fig.
2-6.
3.
Remove
the
rear
panel
in
the
arrow
direction
by
loosening
the
three
screws
(
©
)
as
shown
in
Fig.
2-6.
4.
Loosen
the
two
screws
(
®))
as
shown
in
Fig,
2-4,
antenna,
NX
=
\
fm
(a-m)
front-end/
| i-f amp/MPX and
_” preamplifier board
Fig.
2-6.
Fm
(a-m)
front-end/j-f
amp/MPX
and
preamplifier
board
removal
5.
6.
Remove
the
two
screws
(B))
as
shown
in
Fig.
2-5.
Carefully
remove
the
board
from
the
chassis
taking
care
not
to
break
the
lead
wires.
2-5.
POWER
SUPPLY
BOARD
REMOVAL
1.
Remove
the
wooden
case
as
described
in
Procedure
2-1.
.
Unsolder
the
three
lead
wires
(red,
white
and
black)
connecting
the
power
supply
board
and
the
fm
(a-m)
front-end/i-f
amp/MPX
and
preamplifier
board.
.
Unsolder
the
ribbon
antenna
as
shown
in
Fig.
2-6.
-
Loosen
the
three
screws
(
©)
as
shown
in
Fig.
2-6.
.
Carefully
open
the
rear
panel
in
the
arrow
direction
shown
in
Fig.
2-6
taking
care
not
to
break
the
lead
wires,
.
Remove
the
two
screws
(B
3
x
5)
securing
the
power supply board.
2-6.
DIAL
CORD
RESTRINGING
1,
10.
11.
Remove
the
wooden
case,
front
panel
and
front
subchassis
as
described
in
Procedures
2-1,
2-2
and
2-3.
.
Make
a
loop
of
the
dial
cord
as
shown
in
Fig.
2-7.
.
Make
a
knot
and
hook
a
spring
to.
the
dial
cord
and
then
fasten
the
knot
as
shown
in
Fig.
2-8.
.
Loosen
the
two
screws
securing
the
dial
scale
ass’y
to
the
tuning
drum
shaft
and
remove
the
dial
scale
ass’y.
-
Hook
the
spring
to
the tab
on
the
dial
scale
ass’y
and
string
the
dial
cord
around
the
dial
scale
ass’y
and
the
tuning
shaft
in
numerical
order
as
shown
in
Fig.
2-9
and
2-10.
.
Install
the
dial
scale
ass’y
to
the
tuning
drum
shaft
and
fix
a
dial
scale
set
screw
temporarily.
.
Set
the
AFC
switch
to
OFF.
.
Tune
the
set
to
the
local
fm
station
by
turning
the
tuning shaft.
Loosen
the
dial
scale
set
screw
and
turn
the
dial
scale
ass’y
to
the
position
where
the
fm
pointer
on
the
dial
front
glass
indicates
the
local
fm
station’s
carrier
frequency.
Fix
the
two
dial
scale
set
screws.
Make
sure
that
the
correct
dial
calibration
is
also
done
at
a-m
mode.

dial cord
317 mm (1242) hot
0.3 mm ( Yea) dia.
Fig. 2-7. Dial cord
2
the dial cord.
Fig. 2-8. Finish point of dial cord
dial cord
dial scale ass‘y
!
|
yvatt
two turns
Fig. 2-10. Dial cord restringing (Front View)
2-7. DIAL LAMP REPLACEMENT
1.
Remove the wooden case and front panel as
described in Procedures 2-1 and 2-2.
. Slide the lamp socket forward to permit removal
of lamp as shown in Fig. 2-11.
. Unscrew the lamp from the socket and install a
new one and push the socket back to its original
place.
Fig. 2-11. Dial lamp removal
2-8. TUNER INPUT METER REPLACEMENT
1. Remove the wooden case and front panel as
described in Procedures 2-1 and 2-2.
. Unsolder the two lead wires and remove the two
screws as shown in Fig. 2-12.
. Install a new one.
2-9. BAND, MODE, AFC AND POWER
- WwW
SWITCH REPLACEMENT
. Remove the wooden case and front panel as
described in Procedures 2-1 and 2-2.
. Remove the two screws securing each switch to the
chassis as shown in Fig. 2-13.
. Unsolder the switch lead wires.
Install a new one.
_)

B3x 6,
self-tapping
TUNER INPUT
meter
B3x6é
self-tapping
TUNER INPUT
"Q Of meter eile
Fig.
2-12.
Tuner
input
meter
replacement
Fig.
2-13.
BAND,
MODE,
AFC
and
POWER
switch
replacement
2-10. CHASSIS LAYOUT a-m bar antenna
fm (a-m] front-end/i-f amp/MPX attenuator
and preamplifier board board
power supply
board
power transformer
Fig. 2-14. Chassis layout

SECTION 3
ALIGNMENT AND ADJUSTMENT
3-1. FM I-F AND DISCRIMINATOR Simel oorerster menos «
ALIGNMENT : ;
S Test Equipment Required
CAUTION
1, Signal generator capable of generating a 10.7 MHz
The ceramic filters in the fm i-f circuit are a-m/fm signal.
selected according to their specified center fre-
quencies and color coded as shown in Fig. 3-1 2. Oscilloscope
and listed in Table 3-1. Check the color code of Vertical sensitivity 100 mV/cm minimum
the filters to identify the same center frequency nae
when replacing any of these filters. 3. Ac VIVM
4. Alignment tools
TABLE 3-1.
FM I-F CERAMIC FILTERS Preparation:
Part No. Color Specified Center Freq. 1. Connect the input cable of the oscilloscope with
Higator cli -
ees sana ie 10.70 MHz alligator clips to R229 and ground on the fm (a-m)
front-end/i-f amp/MPX and preamplifier board, and
ESgeaeee! pits sp tetales solder a 0.02 uF capacitor across these clips as '/.
1-527-220-3 1 orange 10.73 MHz aye Fi P P ;
1-527-220-41
black
10.64
MHz
ai
Re:
1-527-220-51 white 10.76 MHz 2. Connect the output cable of the generator across
CV102 on the fm (a-m) front-end/i-f amp/MPX
and preamplifier board through a 0.02 uF coupling
. capacitor as shown in Fi
color dot a BPR 5 AMES AER
Fig.
3-1.
Color
dot
on
ceramic
filter
y
;
€
iz) 02 uF
S% ‘er fzas R2 Rel
a-M osc
trimmer
Fig. 3-2. Interruption of fm or a-m local
oscillator operation
Note: Local oscillator should be killed when
performing this alignment. To stop the
local oscillator operation, shunt the oscil-
lator capacitor with a 0.02 UF capacitor
as shown in Fig. 3-2. To rf signal {
generator
Fig. 3-4. 10.7-MHz signal injection

Procedure:
1.
With
the
equipment
connected
as
shown
in
Fig.
3-5,
set
the
signal-generator
controls
as
follows:
Frequency........
Specified
frequency
of
ceramic
filter.
See
Table
3-1.
Modulation
.......
Fm,
400
Hz,
100
%
(75
kHz)
Output
level.......
1,000
nV
(60
dB)
2.
Set the
tuner
switches
as
follows:
BAND
switch......
FM
MODE
switch......
MONO
AFC
switch
.......
OFF
3.
Adjust
the
signal
generator
frequency
slightly
to
obtain
a
maximum
output,
and
then
change
the
signal
generator
modulation
to
a-m,
400
Hz
30
%.
4.
If
the
discriminator
transformer
IFT201
is
not
aligned
correctly,
400
Hz
ripple
will
be
observed
as
shown
in
Fig.
3-6.
5.
Turn
the
secondary
side
core
(green)
of
discrimina-
tor
transformer
IFT201
(see
Fig.
3-10)
with
an
alignment
tool
to
obtain
a
minimum
indication
on
the
oscilloscope
as
shown
in
Fig.
3-6.
Fig.
3-6.
Fm
discriminator
alignment
output
response
Note:
Turn
the
core
carefully
and
slowly
because
the
output
appearing
on
the
oscilloscope
jumps
up
and
down
when
turning
the
core.
This
might
cause
diffi-
culty
in
determining
the
point
of
mini-
mum
output.
Also,
at
both
extreme
positions
of
the
top
core,
decreased
out-
put
will
be
observed.
The
real
null
point
should
be
obtained
in
the
middle
of
the
rf
eae
signal
Cv102
generator
=
OQ-—-__~__—____—__.
R229 |
core
thread
length,
and
maximum
output
occurs
at
each
side
of
the
true
null
point.
6.
Change
the
signal
generator
modulation
to
fm,
400
Hz
100
%.
7.
Turn
the
core
of
fm
IFT101
and
primary
side
core
(brown)
of
discriminator
transformer
IFT201
(see
Fig.
3-10)
to
obtain
the
maximum
output.
3-2.
FM
FREQUENCY
COVERAGE
AND
TRACKING
ALIGNMENT
Note:
Before
starting
this
alignment,
the
fm
i-f
and
discriminator
alignment
should
be
performed.
Test
Equipment
Required
1.
Fm
signal
generator
2. Ac VTVM
3. Oscilloscope
4. Alignment tools
Preparation:
1.
Connect
the
equipment
as
shown
in
Fig.
3-7.
2.
Set
the
tuner
switches
as
follows:
BAND
switch...
...
FM
MODE
switch.
.....
MONO
AFC
switch...
2...
OFF
Signal
Generator
Method
Follow
the
procedures
given
in
Table
3-2
when
performing
this
alignment
with
an
fm
signal
generator.
Be
sure
that
the
dial
is
mechanically
calibrated.
Off-the-Air Signal Method
Accurate
dial
calibration,
and
a
frequency
cover-
age
test
can
also
be
performed
by
utilizing
off-the-air
local
fm
signals.
However,
before
performing
the
following
procedure,
be
sure
that
the
dial
is
mechani-
cally
calibrated.
oscilloscope
PAA
Fig.
3-5.
Fmi-f
and
discriminator
alignment
test
setup
by
rf
signal
generator

ST-88 ac VTVM oscilloscope
fm oO ——“-"— 0 — 0
signal ANTENNA NORMAL OUTPUT IN
ma
er
generator
©
Jack
(J802)
Lo
Fig. 3-7. Fm frequency coverage and tracking alignment test setup
TABLE 3-2. FM FREQUENCY COVERAGE AND TRACKING ALIGNMENT
SG Coupling.....
re SG Output Level .. 400 Hz, 100 % mod; as low as possible
Step SG Frequency Dial Indication Ac VTVM Adjust Indication
Connection
87.5 MHz 87.5 MHz NORMAL OSC coil L103 Maximum
OUTPUT
See
Fig.
3-10.
VTIVM
2
108
MHz
108
MHz
jack
(J802)
FREQUENCY COVERAGE ALIGNMENT
reading
OSC trimmer CT103
See Fig. 3-10.
SG Coupling..... Direct
SG Output Level .. 400 Hz, 100 % mod; as low as possible
~~ TRACKING ALIGNMENT
87.5 MHz 87.5 MHz NORMAL
OUTPUT
jack (J802)
108 MHz 108 MHz
3-3. FM STEREO SEPARATION ADJUSTMENT
Maximum
VTVM
reading
Antenna coil L101
RF coil L102
See Fig. 3-10.
Antenna trimmer CT101
RF trimmer CT102
See Fig. 3-10.
Procedure:
1. Precisely tune the set to the carrier frequency of
stereo signal generator, then turn the top core of
switching transformer L301 (see Fig. 3-10) to
obtain maximum output at the left channel. Note
that this adjustment has a close relationship with
stereo distortion.
Test Equipment Required
1, Fm stereo signal generator
2. Ac VTVM
3. Oscilloscope
2. Record the output level of the left channel when
the stereo signal generator input selector is set to
the left channel.
Preparation:
1. Remove the wooden case as described in
Procedure 2-1 on page 2. k : ;
a 3. Switch the stereo signal generator input selector
. Connect the test equipment as shown in Fig. 3-8,
then set the fm stereo signal generator controls
as follows:
Carrier frequency ... 98 MHz
Output level.......- 1,000 nV (60 dB)
Mode ........-.-- Stereo
Audio (400 Hz) Mod . 67.5 kHz (90 %)
Pilot (19 kHz) Mod... 7.5 kHz (10 %)
Note: 75 kHz (100 %) if the metering indicates
total modulation (audio-pilot).
to the right channel and read the residual signal
level in the left channel.
. The output-level to residual-level ratio represents
the separation. Adjust separation adj. control
RV501 (see Fig. 3-10) for minimum residual level.
Check the right channel for separation. Usually,
about an 8 to 9 dB difference in channel separation
exists. Readjust RV501 for minimum difference
between left- and right-channel separation. While
Ww
r