NAD T 751 User manual

NAD
SERVICE MANUAL
T 751
SURROUND
SOUND RECEIVER
T 751 SURROUND SOUND RECEIVER

2
SERVICE SAFETY PRECAUTIONS
1. Replacing the fuses
CAUTION: FOR CONTINUED PROTECTION AGAINST THE RISK OF FIRE REPLACE ONLY
WITH SAME TYPE OF FUSE.
Reference No Part Number Description
M751*AH 5120-0200-0 Fuse 5A 125V Time Lag 5x20 MM MITI/UL/CSA
M754*AH 5120-0052-0 Fuse 1.6A 250V Time Lag 5x20 MM UL/CSA
M752*C 5120-0024-0 Fuse 3.15A 250V Time Lag 5x20 MM SEMKO/VDE
NOTE:
<*AH > : USA, CANADIAN MODEL ONLY.
<*C > : EUROPEAN MODEL ONLY.
2. Safety check out
(Only U.S.A. model)
Before returning the product to the customer, make leakage current or resistance measurements
to determine that exposed parts are acceptably insulated from the supply circuit.
Parts marked with the symbol are critical with regard to the risk of fire and electric shock.
Replace only with parts recommended by the manufacturer.
CONTENTS
DESCRIPTION PAGE
SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-4
REAR PANEL / FRONT PANEL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
DISASSEMBLY INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
WIRING DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-8
BLOCK DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
ADJUSTMENT POINTS DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
INSTRUMENT SETUP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
ALIGNMENT PROCEDURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-12
IMPORTANT NOTES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
PCB LAYOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13-19
SCHEMATIC DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-38
IC BLOCK DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39-46
ELECTRICAL PARTS LIST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47-69
EXPLODED VIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .70
EXPLODED VIEW PARTS LIST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71-72
PACKING DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73

3
SPECIFICATIONS
POWER AMPLIFIER AND PREAMPLIFIER SECTIONS
Rated distortion (THD 20Hz-20 kHz FC/C/FR) ≤0.08%
(THD 20Hz-20 kHz SL/SR) ≤0.3%
Input Sensitivity (ref. 8 ohms, 1 kHz) 180+/-30 mV
S/N Ratio (A-wtd, 1KHz, 1W, 8 ohm) ≥-76 dB
(A-wtd, 1KHz, 70W, 8 ohm) ≥-90 dB
Frequency Response (20 Hz - 20 kHz) 0 ± 0.8 dB
Channel Balance (1 dB to -40 dB, 1 kHz) ≤2 dB
(-41 dB to -50 dB, 1 kHz) ≤3 dB
Audio muting at 1kHz ≥53 dB
Headphone O/P in 0.1%, 600 ohm load, CD in 500mV, 1 kHz ≥10V
Subwoofer out, 500mV in (THD at 2V O/P, 100 Hz) ≥0.5%
(S/N at 2V O/P, 100 Hz) ≥80 dB
Crosstalk (2V input, 10W, 1 kHz) > -68 dB
Continuous average power output 70 W
Controls
Bass (at 500mV in, 1W out, 100 Hz) ±9dB
Treble (at 500mV in, 1W out, 10 kHz) ±9dB
SURROUND SECTION
Channel separation
I/p mode : L, R : 1V in, 1 kHz, Ch R, L ≥45 dB
: o/p at unexpected, 1 kHz, Ch C ≥35 dB
I/p mode : L= -R : 1V in, 1 kHz, Ch R, L ≥28 dB
: o/p at unexpected, 1 kHz, Ch C ≥30 dB
I/p mode : L= R : 1V in, 1 kHz, Ch R, L ≥45 dB
: o/p at unexpected, 1 kHz, Ch SL, SR ≥30 dB
Frequency Response
I/p mode : L, R : 1V in, 1W, Ch R, L 40Hz 0 ± 1.5 dB
20kHz 0 ± 0.8 dB
I/p mode : L= R : 1V in, 1W, Ch C 300Hz 0 ± 0.8 dB
20kHz 0 ± 0.8 dB
I/p mode : L= -R : 1V in, 1W, Ch SL, SR 30Hz 0 ± 1.0 dB
6.5kHz -3 ± 1.0 dB
S/N Ratio ( 200mV in, 1, A-WTD w/ 1k termination)
I/p mode : L, R : 1 kHz, Ch L, R ≥65 dB
I/p mode : L=R : 1 kHz, Ch C ≥65 dB
I/p mode : L=-R : 1 kHz, Ch SL, SR ≥65 dB
THD (2.2V in, 1W, w/ 80 kHz LPF, 1 kHz) ≤0.2%
AC-3/DTS SECTION
Frequency Response
FL, FR, C, SL, SR: 200Hz 0 ± 0.8 dB
20kHz 0 ± 0.8 dB
Distortion 1W all channels 0.08%
S/N 1 W ( CCIR/ARM, 200 Hz NOTCH & 400 Hz HPF) ≥85 dB

4
AM TUNER SECTION
Input level is expressed as the reading in open-circuit
of 75-ohm source impedance signal generator
Usable sensitivity (999/1000kHz) ≤30 dBµ
S/N Ratio (5mV in) ≥38 dB
THD (5mV in) ≤3%
IF Rejection (450 kHz) ≥36 dB
Image Rejection (F+2xIF) ≥28 dB
Selectivity ≥17 dB
Output 130+/- 20mV
Loop sensitivity (20dB S/N)
999/1000 kHz ≤66 dB
603/600 kHz ≤66 dB
1404/1400 kHz ≤66 dB
Frequency response (100 - 2.3 kHz, 5mV) ± 6 dB
FM TUNER SECTION *C *AH
Input level is expressed as the reading in open-circuit
of 75-ohm source impedance signal generator
Usable Sensitivity ( 98 MHz) ≤15 dBµ ≤15 dBµ
Signal / Noise Ratio Mono ≥72 dB ≥72 dB
(60 dBµ, IHF wtd) Stereo ≥66 dB ≥66 dB
Frequency Response (20 Hz - 15 kHz, 60 dBµ) 0 ± 1.5 dB 0 ± 1.5 dB
Channel Separation (60 dBµ) 100 Hz ≥30 dB ≥30dB
1 kHz ≥38 dB ≥38 dB
10 kHz ≥30 dB ≥30 dB
Alternate Channel Selectivity
(40 dBµ, ±400 kHz) ≥60 dB ≥45 dB
Capture Ratio (40 dBµ) ≤3 dB ≤3 dB
AM Suppression
(60 dBµ, 100% Mod.FM, 30% Mod.AM) ≥48 dB ≥48 dB
Image Rejection (119.4 MHz) ≥85 db ≥40 dB
I.F. Rejection ( 10.7 MHz) ≥78 dB ≥65 dB
Pilot Suppression (60 dBµ) ≥60 dB ≥60 dB
THD (60 dBµ, L=R 75 kHz for AH, 40 kHz Dev for C)
Mono ≤0.25% ≤0.25%
Stereo ≤0.35% ≤0.35%
Auto-Search Sensitivity On ≥24 dBµ ≥24 dBµ
Off ≤15 dBµ ≤15 dBµ
RDS decode Sensitivity ≤26 dBµ ≤26 dBµ
PHYSICAL SPECIFICATIONS
Dimensions (Width x Height x Depth) 435 x 131 x 348mm
Net weight 12.27kg (27 lbs)
Shipping weight 13.63kg (30 lbs)

5
2
1
78
3 4 11 6 125
10 9 14 13
REAR PANEL / FRONT PANEL
REAR PANEL
FRONT PANEL
1. FM & AM ANTENNA
2. AM STEPPING FREQUENCY
3. TAPE 1 & CD INPUTS
4. 5.1 CHANNEL INPUTS
5. VIDEO 1 - VIDEO 4 (AUDIO & VIDEO) INPUTS
6. DIGITAL AUDIO INPUTS
7. AUDIO PRE-OUTS / SUBWOOFER OUT
8. MONITOR OUT
9. FRONT, CENTER & SURROUND SPEAKERS
10. SOFT CLIPPING
11. NAD-LINK INPUT/OUTPUT
12. SWITCHED POWER OUTLETS (*AH ONLY)
13. AC POWER CORD
14. COOLING FAN
1. POWER
2. STAND-BY
3. DISPLAY
4. FM MUTE / MODE
5. MEMORY
6. PRESET / TUNE
7. DOWN / UP AND
8. VFL DISPLAY
9. VOLUME
10. HEADPHONE SOCKET & VIDEO 5 INPUT
11. AUDIO & VIDEO INPUT SELECTORS & SURROUND
MODE
12. BASS & TREBLE CONTROLS
751

6
DISASSEMBLY INSTRUCTIONS
1. Remove machine screws M 4.0 x 6.0 ( 1 to 6 ) from the side panels.
Remove tapping screw 3.0 x 8.5 ( 7 ) from the back panel.
Refer to Figure No.1.
Figure No.1
2. Pull both sides of the TOP COVER slightly outwards 8 and tilt approx. 35˚ and then remove
in the direction as indicated by the arrow 9 . Refer to Figure No.2.
Figure No.2.
7
6
5
4
1
3
2
9
8
8

SURROUND
AMPLIFIER
PCB
AC OUTLET PCB
(*AH ONLY)
J708B
M001
C834
TRIGGER
PCB
FRONT
AMPLIFIER
PCB
AC3/DTS PCB
VOLUME PCB
POWER SWITCH PCB
87
WIRING DIAGRAM

OSC RF
9
BLOCK DIAGRAM
DIR
CS-8414
DIG SW
74HC153
DSP
CS-4926
PSU
&
ISC
MONITOR
OUTPUT
VIDEO
INPUTS
DIGITAL
INPUTS
OSD
LC74763
2CH ADC
CS-5331 TC-9273
ANALOG
SWITCH
TUNER
SUBWOOFER
LA1837
LC7218
LC72723
VIDEO SWITCH
BA7625
(4cs)
DAC
CS4340
3pcs, 6ch tot
6CH
VOLUME
M62447SP
5CH
POWER
AMPLIFIER
MCU
LC87F65C8A
VFL DISPLAY NAD LINK
IN/OUT
REMOTE
SENSOR
KEY
MATRIX
MUTING 5.1CH
INPUT
EEPROM
VIDEO
OUTPUTS
AUDIO
INPUTS
AUDIO
OUTPUTS
10
ADJUSTMENT POINTS DIAGRAM
1. TUNER
2. IDLE CURRENT - Front Amplifier & Surround Amplifier Board

11
ALIGNMENT PROCEDURES
AMPLIFIER SECTION
Idle Current
Step Item Connection Adjustment Adjust for
1 Front Left Channel Voltmeter to P502 on Front Amp Board R574 2mV±0.2mV
2 Front Right Channel Voltmeter to P501 on Front Amp Board R573 2mV±0.2mV
3 Center Channel Voltmeter to P503 on Front Amp Board R599 2mV±0.2mV
4 Rear Left Channel Voltmeter to JP801 on Surround Amplifier Board R867 2mV±0.2mV
(PCB N0901C-AMP2)
5 Rear Right Channel Voltmeter to JP802 on Surround Amplifier Board R868 2mV±0.2mV
(PCB N091C-AMP2)
INSTRUMENT SETUP
1. FM MEASUREMENT
Fig. 1
Fig. 2
2. RDS MEASUREMENT
Fig. 3
3. AM MEASUREMENT
Fig. 4
FM
SIGNAL
GENERATOR
ANTENNA
TERMINAL
OUTPUT
TERMINAL
DISTORTION
ANALYZER
DISTORTION
ANALYZER
AC
VOLTMETER
OSCILLOSCOPE
AC
VOLTMETER
OR
OSCILLOSCOPE
AC
VOLTMETER
OR
OSCILLOSCOPE
OUTPUT
TERMINAL
OUTPUT
TERMINAL
L
R
ANTENNA
TERMINAL
ANTENNA
TERMINAL
ANTENNA
TERMINAL
AM LOOP
ANTENNA
(Accessory)
AM LOOP
ANTENNA
60cm
DIGITAL
MILLIVOLT
METER
VT-J914
FM
SIGNAL
GENERATOR
AM
SIGNAL
GENERATOR
FM
SIGNAL
GENERATOR
RDS
GENERATOR
FM
STEREO
GENERATOR
P-901
DC
MILLIVOLT
METER
UNIT
UNIT
UNIT
UNIT

12
IMPORTANT NOTES
1. Show the software version
Press “VIDEO 5” and “EXT 5.1”
and “DISPLAY”.
2. Toggle between PAL and NTSC
Press “MEMORY” and “VIDEO 1”.
3. Light UP all the icon on the VFL.
Press “VIDEO 1” and “EXT 5.1”
and “DISPLAY”.
4. Delete All Tuner Presets
a) Change the setting of
9kHz/10kHz AM step switch
and then switch on the unit.
b) Switch off the unit and put
back the 9kHz/10kHz AM step
switch to the right setting.
Then switch on the unit. (i.e.
9kHz=C ver., 10kHz=AH ver.)
FM/RDS SECTION
- FM mono: 1kHz, 75kHz devi., 60dB/µV
- FM stereo: 1kHz, 67.5kHz devi., 60dB/µV
Pilot signal 19kHz 7.5kHz devi.
OUTPUTS
- Connect the non-inductive type resistor of 8 ohms to the all speaker terminals unless otherwise noted.
Item
FM
IF/RF
Stereo
Distortion
Stereo
Separation
Muting
Level
Signal
output
Step
1DC voltmeter L941 0±100mV
3Distortion
analyzer
Distortion
analyzer
Oscilloscope
Oscilloscope
L942
R956
R941
Minimum
Minimum
2 AC voltmeter IFT on the
front end
IFT on the
front end
Maximum
Maximum
separation
Connection
of instrument
Fig.1 –
–
Fig.2
Fig.2
Fig.1
Channel L
or R 1kHz
99.0MHz
1kHz 75kHz devi.
65dBf (60dB)
99.0MHz Ext.
mod. 65dBf
(60dB)
FM SG
output
Stereo mod-
ulator output
Tuning
frequency
99.0MHz
99.0MHz
Channel L
or R 1kHz
99.0MHz Ext.
mod. 65dBf
(60dB)
99.0MHz Ext.
mod.65dBf(60dB)
RDS 2% MOD
99.0MHz 18dB
99.0MHz
99.0MHz
RDS –
––
–
Fig.3 99.0MHz
Output
indicator
Adjustment
point
Adjust
for Remarks
FM MUTE/MODE
switch: ON/AUTO
Repeat the steps
1 to 3 until no fur-
ther adjustment is
necessary.
FM MUTE/MODE
switch: ON/AUTO
Don’t turn more
than +/-180˚
Repeat stereo
distortion and
stereo separation
alignment until
THD at minimum
and separation at
maximum.
Decode the RDS-
Program Station.
AM SECTION
AM Modulation: 400Hz, 30%
For AH Version
Step
1–
2
3
530kHz
600kHz
990kHz
600kHz
400Hz 30% mod.
60dB/m
AM SG
output
Tuning
frequency
Output
indicator
Adjustment
point
600kHz
400Hz 30% mod.
60dB/m
AC
voltmeter
AC
voltmeter
Digital
DC
voltmeter
L972
OSC coil
on RF
block L971
RF coil
on RF
block L971
Adjust
for
1.35±0.2V
Maximum
Maximum
Step
1–
2
3
522kHz
or
531kHz
603kHz
999kHz
600kHz
400Hz 30% mod.
60dB/m
AM SG
output
Tuning
frequency
Output
indicator
Adjustment
point
600kHz
400Hz 30% mod.
60dB/m
AC
voltmeter
AC
voltmeter
Digital
DC
voltmeter
L972
OSC coil
on RF
block L971
RF coil
on RF
block L971
Adjust
for
1.3±0.2V (522kHz)
1.35±0.2V (531kHz)
Maximum
Maximum
For C Version

13
PCB LAYOUT
SPEAKER BOARD
DIGITAL BOARD
PRIMARY BOARD
SECONDARY BOARD
TONE BOARD

14
PSU BOARD
S-VIDEO BOARD
LED BOARD AC OUTLET BOARD

15
AC3 / DTS BOARD - COMPONENT SIDE
AC3 / DTS BOARD - SOLDER SIDE

16
MULTI-CHANNEL BOARD
MAIN BOARD

17
KEYBOARD - COMPONENT SIDE KEYBOARD - SOLDER SIDE

18
TRIGGER BOARD LOAD BOARD
FRONT AMPLIFIER BOARD
VIDEO 5 BOARD
VOLUME BOARD POWER SWITCH BOARD

19
SURROUND AMPLIFIER BOARD
TUNER BOARD
VIDEO BOARD AUDIO BOARD

20
SCHEMATIC DIAGRAM
(TO KEY J204A) (TO FRONT AMP J504A)
(TO SEC J702A)
LOAD
NOTE: 1. RESISTORS ARE CARBON FILM 5% 1/8W UNLESS OTHERWISE SPECIFIED.
2. CERAMIC CAPACITORS ARE 50V +80/-20%. UNLESS OTHERWISE SPECIFIED.

2221
VOLUME PCB
LED PCB
KEY
NOTE: 1. RESISTORS ARE CARBON FILM 5% 1/8W UNLESS OTHERWISE
SPECIFIED.
2. CERAMIC CAPACITORS ARE 50V +80/-20%. UNLESS OTHERWISE
SPECIFIED.

23 24
AC3 / DTS
NOTE: 1. RESISTORS ARE CARBON FILM 5% 1/8W
UNLESS OTHERWISE SPECIFIED.
2. CERAMIC CAPACITORS ARE 50V 10%.
UNLESS OTHERWISE SPECIFIED.