NAD 7155 User manual

SERVICE
MANUAL
AM/FM STEREO RECEIVER

NAD 7155 SERVICE MANUAL
NOTE: This manual covers all versions.
A: U.S.A.
Al: Canada
B: U.K,
B1: Australia
C: EUROPE and others
C1: W-Germany
TABLE OF CONTENTS
LOCATION MAP
SPECIFICATION
INTERNAL VIEW
SUGGESTED INSTRUMENTATION HOOKUP
FM ALIGNMENTS
AM ALIGNMENTS
AMPLIFIER ALIGNMENTS
AMPLIFIER P.C.B. LAYOUT DIAGRAM
SCHEMATIC DIAGRAM (AMPLIFIER SECTION)
TUNER P.C.B. LAYOUT DIAGRAM
SCHEMATIC DIAGRAM (TUNER SECTION)
WIRING DIAGRAM
EXPLODED VIEW PARTS LIST
EXPLODED VIEW
ELECTRICAL PARTS LIST
PAGE

REAR PANEL
1.
AC
Line
Cord.
9.
Phono
Input.
|
2.
AC
Convenience
Outlets
10.
Phono
Capacitance.
(Not
in
European
models)
11.
CD/Aux
Input.
3.
Speakers
A.
12,
Tape
1
Rec/Play.
4.
Speakers
B.
13,
Tape
2
Rec/Play.
5.
Antenna
Terminals.
14,
Preamp
Out,
Main
In
6.
AM
Rod
Antenna.
15.
Soft
Clipping.
7.
Phono
Ground.
16.
Speaker
Impedance.
8.
MM/MC.
17.
Bridging.
6 7 5
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FRONT PANEL
1, Power.
Phones.
Speaker Selector.
Bass.
Treble.
Bass EQ.
Infrasonic Filter Defeat.
. Mono.
. Dyn Sep Defeat.
10. Recording Input Selector.
11. Listen Input Selector.
‘Service PERSONNEL
12, Low Level.
43. Loudness Compensation.
14. Volume/Balance.
15. Tuning Display.
16. Status Indicators.
17. Pre-sets.
18. Enter.
19. AM/FM
20. Up/Down Tuning.
21. Search.
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12 13

SPECIFICATIONS
NOTE: Measurements referenced to 8 ohms are taken with the Speaker Impedance Selector set to “8 ohm (High).
Measurements for 4 and 2 ohms are taken with the impedance selector at ‘4 ohm (Normal)’’. Specifications
are measured in accordance with EIA Standard RS-490 (IHF A-202) for amplifiers and ANSI-IEEE Standard
185 (1975) (IHF T-200) for tuners, Tuner sensitivity is measured via 75 ohm coaxial input and converted to
equivalent 300 ohm values.
Power Amplifier Section, Stereo Mode
CONTINUOUS AVERAGE POWER OUTPUT INTO 8 OHMS
(min. RMS power per channel into 8 ohms, 20 Hz - 20 kHz,
both channels driven, with no more than the rated distortion).
Rated distortion (THD), 20 Hz - 20 kHz.
Clipping power (max. continuous power per channel). 8 ohms:
4 ohms:
IHF dynamic headroom at 8 ohms.
IHF dynamic power (max. short-term power per channel).
8 ohms:
4 ohm:
2 ohms:
Slew factor.
Slew rate.
Damping factor (ref. 8 ohms, at 50 Hz).
Input impedance.
Input sensitivity for 1 W/55 W out.
Power amp. gain.
THD (Total Harmonic Distortion, 20 Hz - 20 kHz, from
250 mW to rated output).
SMPTE I.M. (Intermodulation Distortion 60 Hz : 7 kHz,
4:1, from 250 mW to rated output).
IHF I.M. (CCIR IM Distortion, 19 to 20 kHz at rated output).
Bridged (Monophonic) Mode
CONTINUOUS AVERAGE POWER OUTPUT INTO 8 OHMS
(min. RMS power into 8 ohms, 20 Hz - 20 kHz, with no more
than the rated distortion).
IHF Dynamic Headroom at 8 ohms.
Dynamic power (max. short-term output, 8 ohms).
All versions except USA.
55 W (17.4 dBW)
0.03 %
65W
75 W
+2.6dB
100 W
100 W
130 W
> 50
20 V/usec.
> 50
22 k ohms.
0.13 V/0.95 V
26.8 dB.
< 0.03 %
< 0.03 %
<0.03 %
125 W (21 dBW)
+2.5dB
250 W
USA version only.
55 W (17.4 dBW)
0.03 %
75W
90W
+3dB
110 W
130 W
150 W
150 W (22 dBW)

Preamplifier Section
Phono Input
Input impedance,
Input sensitivity (1 kHz),
Input overload at 20 Hz/1 kHz/20 kHz.
THD (20 Hz - 20 kHz) and IM Dist. at +30 dB level.
RIAA response accuracy.
S/N ratio, IHF A-weighted, with cartridge connected.
Line Level Inputs (Aux., Tape)
Input Impedance.
Input sensitivity.
Maximum input signal.
Signal to noise ratio, A-weighted.
Frequency response, 20 Hz - 20 kHz.
Outputs
Preamp output impedance.
Maximum output level.
Tape output impedance.
Tape output infrasonic filter.
Controls
Treble.
Bass,
Speaker equalization.
Infrasonic filter.
Audio muting (low level).
MM:
Mc:
MM:
MC:
MM:
Mc:
MM:
MC:
R 47k ohms
C 100/200/320 pF
R 100 ohms
C 1000 pF
0.33 mV for 1 W out.
2.5 mV for 55 W out.
0.02 mV for 1 W out.
0.15 mV for 55 W out.
27 mV/230 mV/2 V.
1.2 mV/12 mV/88 mV.
<0.04 %
+0.5 dB.
80 dB re 5 mV.
80 dB re 0.5 mV.
R 10kohms;C 220 pF.
20 mV for 1 W out.
150 mV for 55 W out.
>10V
88 dB re 1 W.
103 dB re 55 W.
+0.5 dB.
800 ohms.
10 Vv.
1000 ohms (buffered).
—3dB at 15 Hz, 12 dB/octave.
+7 dB at 10 kHz.
+7 dB at 100 Hz.
+3 dB at 70 Hz.
+6 dB at 32 Hz.
— 3B at 15 Hz, 12 dB/octave.
— 20 4B.
EM Tuner Section
Input sensitivity
Mono, —30 dB THD +N:
Capture ratio at 25, 45 & 65 dBf.
AM rejection.
Selectivity,
Image rejection.
R. F. intermodulation.
|. F, rejection.
SCA rejection.
Subcarrier suppression (19 + 38 kHz).
THD at 100 % modulation,
Signal to noise ratio, A-weighted, 65 dBf.
Frequency response, 30 - 15 kHz.
Stereo separation (Dyn Sep off),
AM Tuner Section
Usable sensitivity.
Selectivity.
Image rejection.
|, F, rejection.
Physical Specifications
Dimensions (width x height x depth).
Net weight.
Shipping weight.
Power consumption.
Mono, 50 dB S/N:
Stereo, 50 dB S/N:
Stereo, 60 dB S/N:
Alternate channel:
Adjacent channel:
Mono:
Stereo:
Mono:
Stereo:
1 kHz:
30 Hz - 10 kHz:
50 usec. deemphasis 75 psec.
10.3 dBf. 9.8 dBf.
(1.8
#V/300
ohms)
(1.7
#V/300
ohms)
15.8 dBf. 13.2 dBf.
(3.2 nV) (2.5 uv)
33.2 dB. 32 dBf.
(25 nV) (22 uv)
43.1 dBf. 42 dBf.
(78 nV) (70 pv)
<1,.5 dB.
> 65 dB.
70 GB.
8 dB.
85 dB.
70 dB.
90 GB.
70 dB.
60 dB.
1 kHz 100 Hz - 6 kHz
0,09 % 0.2%
0,09 % 0.3%
82 dB.
75 dB.
(typ. 80 dB at 75 dBf)
+0.5 dB.
50 dB.
40 dB.
300 uV/meter.
35 dB.
50 dB.
50 dB.
42 x 10.8 x 38 cm.
16.5 x 4.25 x 15 in.
9.18 Kg./20 Ib, 4 oz.
10.6 Kg./23 Ib. 6 oz.
50/60 Hz at 110, 120, 220 or 240 VAC.
340 W.

INTERNAL VIEW
SUGGESTED
INSTRUMENTATION
HOOKUP
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' OSCILLOSCOPE FM GENERATOR AUDIO OSC |
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1 \ 1
IN
(0)
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t
USE
ONLY
IF
FM
GENERATOR
WITH
BUILT-IN
SWEEP
UNAVAILABLE
:
OSCILLOSCOPE
FM GENERATOR
WITH BUILT-IN SWEEP
Rd IE: ST 10008
SWEEP
Y INPUT X INPUT [OUTPUT RF OUT.
VERT. HORIZ, $ ¢ °
DETECTOR
PROBE
BALUN
AC.
VTVM
esa fas ee cere he
PIN1 IC 102 3000
UNIT UNDER TEST
AC VTVM
INPUT
FROM
TUNER IC:
TO PIN1
Ic 102
TO TUNER GND.
AT FRONTEND
out
TO SCOPE
DISTORTION METER
DISTORTION
PUT Out
ry
PUT
Diodes should be point-contact
germanium; Some commonly
available types are:
PICTORIAL DIAGRAM OF DETECTOR PROBE
RY
c2
CENTER LEAD
TO SCOPE
\ SHIELD
Keep leads as shortas
minimize stray signal
0a80
OA81
AAIIS
1N60
1N34
1N22
possible, to
pickup.

FM ALIGNMENTS
NECESSARY INSTRUMENTATION
FM GENERATOR (less than 0.05% THD)
STEREO GENERATOR (less than 0.05% THD, more than 50 dB sep.)
AUDIO GENERATOR (not necessary if FM generator has built in sweep; ie, SOUND TECHNOLOGY ST 1000A and
ST 1020A)
AC VTVM's (or one with a left/right switch)-
THD ANALYZER (resolution less than 0.1%)
OSCILLOSCOPE (5mV or better sensitivity, X input capability)
FREQUENCY COUNTER
VOM or DMM (high impedance, must read in mV)
DETECTOR PROBE
IMPORTANT
FRONTEND
oa
While all FM generator output levels hereafter are referred to the 300 ohm input, 75 ohm input
can be used, but be aware of possible equipment groundloops and divide the RF output levels
by 2.
Before alignments commence set input selector and record selector to tuner and release mono
dyn sep defeat switches (out).
Alignment of frontend should only be necessary after repair to frontend or crystal oscillator
circuits (pin 2 and 3 on IC 110).
TUNING VOLTAGE (OSCILLATOR)
It is essential to check tuning voltage before aligning the rest of the frontend.
Connect DMM between ground and TP 102.
Tune to 108 MHz and adjust C 20 if voltage is incorrect.
SPECIFICATION 24.7V + 0.5V
Tune to 88 MHz and read voltage. Adjust L 6 if voltage is incorrect.
SPECIFICATION 3.6V + 0.5V>
Repeat step 2 and 3 until readings are within tolerances.
RF ADJUSTMENT (TRACKING)
Connect RF generator to 300 ohm antenna input and detectorprobe to pin 1 IC 102 with ground to
tunershield. Adjust sensitivity of oscilloscope to maximum (SmV or better) and modulate FM generator
sweep * 300 kHz or more.
Set tuner to 105 MHz, enter into preset 5, and tune generator so that curve appears on oscilloscope.
Turn down RF input level so that curve covers approximately 1/2 of oscilloscope display.
Adjust C 3,C 9, C 11 and C 15 to maximum curve height while reducing RF input to keep entire curve
on display.
Set tuner to 90 MHz, enter into preset 1, and tune generator so that curve appears on oscilloscope display.
Adjust L 1, L 2, L3 and L 4 to maximum curve height.
Repeat steps 2, 3, 4 and 5 (use preset 1 and 5) until both frequencies are at maximum curve height.
NOTE: 105 MHz curveheight is typically slightly stronger than 90 MHz.
IF ADJUSTMENT
Set tuner to approximately 98 MHz (the tuner must be tuned to an unoccupied frequency) enter into
Preset 3, and tune FM generator to display a curve on oscilloscope.
Adjust L 5 and L 101 to maximum and symmetrical curve on the display, using as little input as
Possible.
NOTE: Maximum input 500 yV, typical curveheight 4 mV at 150 uV and 15 mV at 300 nV.
|
i

DETECTOR COARSE ADJUSTMENT (OPTIONAL, NEEDED ONLY IF DETECTOR WAS REPAIRED)
Reduce sweep modulation level to + 75 kHz and set input level to 300 uV.
Adjust FM generator frequency so that both legs of the inverted U-shaped curve are equally high on the
display. The curve should be almost perfectly symmetrical.
Disconnect
detectorprobe
from
tuner
and
oscilloscope.
Connect
either
of
the
tape
1
rec.
outputs
to
the
oscilloscope.
The
oscilloscope
should
now
display
a
diagonal
line.
Adjust
L
102
primary
(closest
to
IC
102)
to
maxi-
mum curveheight
and
L
102
secondary
to
minimum
curve
height
and
straightest
possible
line.
Go
back
and forth
between
primary
and secondary
till
both
are peaked.
NOTE: Both the cores should be within 1.5mm from the top of the form.
DETECTOR ALIGNMENT (FINAL)
Disconnect detectorprobe and connect tape 1 rec. output to VTVM’s, oscilloscope and distortion
analyzer.
Switch
stereo
generator
to
1
kHz
100%
(+
75
kHz)
mono
modulation
and
oscilloscope
to
normal
internal
sweep
0.2
mS
and 0.5
V/cm sensitivity.
Detector reference frequency.
Reduce FM generator output level while monitoring THD from left channel. When THD increases to 3%,
fine tune the FM generator frequency to minimum THD. Reduce FM generator output level and fine
tune till no reduction in the 3% THD can be achieved by fine tuning. Use this frequency for all the follow-
ing detector, MPX and DYN SEP adjustments.
NOTE: The typical input level for this 3% THD should be 1.6 pV to 2.3 KV. This is done only to “line
up” the frequency from the generator to the tuner’s frequency.
lf IHF usable sensitivity (-30 dB THD + N = 3.16%) is to be verified, a proper IHF bandpass-
filter must be used.
Connect DMM across TP 104 (negative) and TP 105 (positive). Set FM generator output to 1000 uV
Adjust L 102 primary (closest to IC 102) for 0 V on DMM.
TOLERANCE +50 mv
Adjust L 102 secondary for lowest THD.
SPECIFICATION less than 0.1%
Repeat steps 3, 5 and 6 till no further improvements. Record the DMM's final reading for use later in
the adjustments. (1 — 3)
AUTOSEARCH LEVEL
Connect DMM between ground and TP 107,
Increase FM generator level upwards from 0 and adjust R 107 “MUTE” so that DMM reading goes from
0 V to approximately 4.8 V at 10 uV input.
TOLERANCE £2uv
STEREO DECODER, MPX FILTERS.
vco.
Connect a frequency counter and a 200 k ohm resistor in parallel between ground and TP 108.
Set FM generator to 1000 uV output and no modulation.
Adjust R 164 “MPX VCO” for a 19000 Hz reading on the counter.
TOLERANCE +100 Hz
Disconnect frequency counter and resistor and depress DYN SEP defeat switch (in).
Stereo switch threshold.
Modulate FM generator 1 kHz 100% left only plus 19 kHz pilot 8 - 10%.

6
14
Increase
FM
generator
level
upwards
from
0
and
adjust
R
167
“ST
SW”
so
that
stereo
light
turns
on
and
audio
outputs,
as
watched
on
VTVM’s
and
oscilloscope,
switches
to
one
channel
only
at
10
uV
input
level.
TOLERANCE +5 uv
NOTE:
When
turning
input
level
down
the
unit
will
switch
into
mono
at
a
lower
level,
typically
7
uV.
Stereo separation.
Set FM generator output to 1000 uV, modulate left channel only.
Adjust R 158 for minimum on right channel VTVM.
Modulate
FM
generator
right
channel
only
and
adjust
R
158
for
minimum
on
left
channel
VTVM.
If
the
minimum
in
step
8
and
9
are
different,
adjust
R
158
so
that
the
readings
are
the
same
in
both
channels.
SPECIFICATION better than 50 dB separation
MPX filter
Turn
off
audiomodulation,
leaving
pilot
tone
only.
Disable
IHF
filter,
or
external
19
kHz
filter.
Check
19/38
kHz
suppression.
SPECIFICATION
more
than
60 dB
If
unit
does
not
meet
specification
adjust
FL
102
“MPX
FILTER”
on
left
channel
and
FL
103
“MPX
FILTER”
on
right
channel
to
minimum
output.
NOTE:
DO
NOT
ADJUST
THE
MPX
FILTERS
UNLESS
NECESSARY,
the
cores
are
brittle
and
break
easily.
Release the DYN SEP DEFEAT switch (out).
DYN SEP ADJUSTMENTS.
Turn
R
256
“DYN
SEP
OFF”,
R
249
and
250
“DYN
SEP”
fully
clockwise.
DYN SEP separation effect.
Observe
output
from
left
channel
with
FM
generator
output
level
1000
nV
and
modulated
1
kHz
left
channel
only.
Reduce
audiomodulation
only
from
stereo
generator
so
that
left
channel
output
is
reduced
by
6
dB
(50%
stereo
modulation).
The 19 kHz pilot signal MUST REMAIN modulated 8 - 10%.
Set
FM
generator
output
to
50
nV
and
adjust
R
249
“DYN
SEP”
for
—30
dB
separation
left
to
right
channel.
TOLERANCE +2dB
Switch
modulation
to
right
channel
only
while
maintaining
the
same
modulation
levels:
Adjust R 250 “DYN SEP” for —30 dB separation right to left channel.
TOLERANCE +2dB
DYN SEP auto defeat level.
Set
generator
output
to
200
uV
and
adjust
R
256
“DYN
SEP
OFF”
so
that
separation
starts
increasing
when
watching
left
channel
VTVM.
Adjust
FM
generator
output
up
and
down
around
200
uV
and
make
sure
switching
occurs
around
200
HV.
TOLERANCE +100 nV — 30 nV
SYNTHESIZER FREQUENCY
Tune
to
a
known
accurate
frequency
source,
i.e.,
broadcasting
station
or
synthesized/digital
display
FM
generator
preferably
in
the
midband
95
-
100
MHz.
Connect DMM across TP 104 (negative) and TP 105 (positive).
Adjust
C
209
“FQ”
so
that
DMM
reads
the
same
as
recorded
in
E
—
7.
TOLERANCE +10mV
R167
TP108

AM ALIGNMENTS
A
wn
aR won
OSCILLATOR.
Connect DMM to TP 101 and gnd.
Tune to 1710 kHz, Enter into preset 1. Adjust C 148 for reading of 31 + 0.5VDC,
Tune to 520 kHz. Enter into preset 2. Adjust L 103 for reading of 1.8 + 0.1 VDC.
Repeat steps 2 and 3 until within tolerances.
ANTENNA, IF
Swing
antenna
away
from
chassis
and
peel
back
label
(if
present)
to
expose
adjustment
tab.
Connect DC voltmeter to centertap, R 208 and gnd.
Tune
to
station
of
moderate
strength,
near
600
kHz.
Enter
into
preset
3.
Adjust
L
951
(move
tab
under
label
on
antenna)
for
maximum
reading
on
meter.
(Use
non-ineractive
tool,
such
as
plastic
or
wooden
stick.)
Adjust L 104 and L 106 for maximum reading on meter.
Tune
station
of
moderate
strength
near
1400
kHz.
Enter
into
preset
4.
Adjust
C
147
for
maximum
reading
on
meter.
Repeat steps 3 and 5 until no further improvement is seen.
9 kHz, 10 kHz WHISTLE FILTERS
Tune to quiet spot on the dial (a clear frequency)
Connect audio osc. to base, Q 117 (isolate with 0.1 - 1.0 uF capa.)
Connect AC VTVM (or scope) to TP 103.
Set
audio
osc.
to
10
kHz
(+
50
Hz)
1
V.
Adjust
FL
104
for
minimum
meter
reading.
Set
audio
osc.
to
9
kHz
(+
50
Hz)
1
V.
Adjust
FL
105
for
minimum
meter
reading.
SIGNAL METER, AUTO STOP
R
208
controls
signal
strength
indication
and
auto
stop
level,
adjust
only
if
necessary,
to
correct
for
scan
stopping
on
excessively
weak
signals,
or
failure
to
stop
on
moderately
strong
ones.
NOTE:
When
finished,
lock
antenna
bar
adjustment
with
laquer
(nail
polish),
re-install
label.
12
TP101