NAD C-425 Service manual
NAD
SERVICE MANUAL
C 425
STEREO
AM/FM TUNER
C 425
STEREO
AM/FM TUNER
- 3 -
SERVICE SAFETY PRECAUTIONS
1. 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
REAR PANEL / FRONT PANEL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
DISASSEMBLY INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
BLOCK DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
WIRING DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
ADJUSTMENT POINTS DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
INSTRUMENT SETUP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
ALIGNMENT PROCEDURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
PCB LAYOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-12
SCHEMATIC DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-14
IC BLOCK DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-18
ELECTRICAL PARTS LIST. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-27
EXPLODED VIEW. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
EXPLODED VIEW PARTS LIST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-30
PACKING DIAGRAM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
- 2 -
SPECIFICATIONS
AM TUNER SECTION
Input level is expressed as the reading in open-circuit
of 75-ohm source impedance signal generator
Usable Sensitivity (999/1000kHz) ≤30dBµ
S/N Ratio (5mV in) ≥38dB
THD (5mV in) ≤3%
IF Rejection (450kHz) ≥36dB
Image Rejection (F+2xIF) ≥28dB
Selectivity ≥17dB
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
Input level is expressed as the reading in open-circuit
of 75-ohm source impedance signal generator
Usable Sensitivity (98 MHz) ≤13 dBµ ≤13 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±1.0 dB 0±1.0 dB
Channel Separation (60 dBµ) 30 Hz ≥33 dB ≥33 dB
1 kHz ≥42 dB ≥42 dB
10 kHz ≥32 dB ≥32 dB
Alternate Channel Sensitivity
(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) ≥65 dB ≥65 dB
Image Rejection (119.4 MHz) ≥85 dB ≥85 dB
I.F. Rejection (10.7 MHz) ≥78 dB ≥78 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
*C
*AH
PHYSICAL SPECIFICATIONS
Dimensions (Width x Height x Depth) 435 x 80 x 285 mm
Net weight 4 kg (8.8 lbs)
Shipping weight 5.1 kg (11.22 lbs)
- 3 -
- 5 -
REAR PANEL / FRONT PANEL
REAR PANEL
1. FM ANTENNA
2. AM ANTENNA
3. OUTPUT
4. IR IN
FRONT PANEL
1. POWER ON / OFF
2. POWER STATUS INDICATOR
3. BLEND
4. MEMORY
5. FM MUTE / MODE
5. 12V TRIGGER IN
6. AC LINE CORD
7. RS-232
6. AM / FM
7. DISPLAY
8. PRESET / TUNE
9. DISPLAY AREA
10. PRESET / TUNE CONTROL
IMPORTANT NOTES
1. Show the software version
Press “BLEND” and “AM/FM”.
2. Light UP all the icon on the VFD
Press “BLEND” & “DISPLAY”.
3. Factory test resets
When VFD all Light press any key.
4. AM Step 10K/9K Change
When AM band, press “AM/FM” & “PRESET/TUNE”.
5. Shipment resets
When pressing “DISPLAY” & “PRESET/TUNE” to VFD all Light, press any key.
- 4 -
5
4
3
1
2
7
6
6
DISASSEMBLY INSTRUCTIONS
1. Remove machine screws M 4.0 x 6.0 ( 1 to 4 ) from the side panels.
Remove tapping screw 3.0 x 8.5 5 from the back panel.
Refer to Figure No.1.
Figure No.1
2. Pull both sides of the TOP COVER slightly outwards 6 and tilt approx. 35˚ and then remove
in the direction as indicated by the arrow 7 . Refer to Figure No.2.
Figure No.2.
- 5 -
- 7 -
AM LOOP ANT FM ANT OUTPUT
FRONT END
ENV172D3G1
VFD
CPU
LC866448B
U201
U202
VFD DRIVER
PT6311
KEY MATRIX
Trigger IN
U203
EEPROM
24C08
PLL
LC72723M
RDS DECODER
U901
AM/FM IF
LA1837
MUTING
IR IN
U701
74HC86
M218
REMOTE
SENSOR
POWER
SUPPLY
VFD
-VP
+5V CPU
+10V
AC INPUT
L
R
VT
VT
ce data clk RDS-CLK RDS-SIG RDS-DATA
MPXIN
data
out
(#1)=Power On
(#1)+(#2)=Standby
LC7218
U903
ST/MO, MUTE, SMETER
TUNE
FM
OSC/IF
AM
OSC/IF
1
27
17
16
23
2
30
U902
21
2 3 4 5
15
11
15
8
10 IN
16 14
20
16
14
22
12/13
5
16 19 24
19 18
BLOCK DIAGRAM
- 6 -
WIRING DIAGRAM
MAIN BOARD
KEY BOARD
DISPLAY BOARD
LED BOARD
TRANSFORMER
POWER SUPPLY BOARD
YELLOW
BLUE
WHITE
- 7 -
- 9 -
ADJUSTMENT POINTS DIAGRAM
OSC RF
VT
- 8 -
FM
SIGNAL
GENERATOR
ANTENNA
TERMINAL
OUTPUT
TERMINAL
DISTORTION
METER
DISTORTION
METER
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_J911
FM
SIGNAL
GENERATOR
AM
SIGNAL
GENERATOR
FM
SIGNAL
GENERATOR
RDS
GENERATOR
FM
STEREO
GENERATOR
P901
OUTPUT
TERMINAL
DC
MILLIVOLT-
METER
UNIT
UNIT
UNIT
UNIT
INSTRUMENT SETUP
1. FM MEASUREMENT
Fig. 1
Fig. 2
2. RDS MEASUREMENT
Fig. 3
3. AM MEASUREMENT
Fig. 4
- 9 -
ALIGNMENT PROCEDURES
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 47Kohm resistor unless otherwise noted.
Item Step
FM
IF/RF
Stereo
Distortion
Stereo
Separation
Mute
Level
RDS Fig.3
Connection
of instrument
1
2 AC voltmeter
3
FM SG
output
99.0MHz
Fig.1
Fig.2
Fig.2
Fig.1 99.0MHz 18dB – 99.0MHz Oscilloscope R956
1kHz 75kHz
devi.
65dBf (60dB)
99.0MHz Ext.
mod. 65dBf
(60dB)
99.0MHz Ext.
mod. 65dBf
(60dB)
99.0MHz Ext.
mod. 65dBf
(60dB)
RDS 2% MOD
Stereo
modulator
output
– 99.0MHz
Channel L
or R 1kHz
Channel L
or R 1kHz
– 99.0MHz – – –
Tuning
frequency
99.0MHz
99.0MHz
Output
indicator
DC voltmeter L941 0±70mV
Distortion
analyzer
Distortion
analyzer
Oscilloscope
Distortion
Meter
Adjustment
point
IFT on the
front end
L942 Minimum
IFT on the
front end
R941
Adjust
for
Maximum
Minimum
Maximum
separation
Minimum
Signal
output
Remarks
FM MUTE/MODE
switch: ON/AUTO
Repeat the steps
1 to 3 until no
further 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 RDSProgram station
AM SECTION
AF Modulation: 400Hz, 30%
For AH Version
Step
1 – 530kHz
2
3
For C Version
Step
1 –
2
3
AM SG
output
600kHz
400Hz 30% mod.
60dB/m
600kHz
400Hz 30% mod.
60dB/m
AM SG
output
600kHz
400Hz 30% mod.
60dB/m
600kHz
400Hz 30% mod.
60dB/m
Tuning
frequency
600kHz
990kHz
Tuning
frequency
522kHz
or
531kHz
603kHz
999kHz
Output
indicator
Digital
DC
voltmeter
AC
voltmeter
AC
voltmeter
Output
indicator
Digital
DC
voltmeter
AC
voltmeter
AC
voltmeter
Adjustment
point
OSC coil
on RF
block M971
RF coil
on RF
block M971
L972 Maximum
Adjustment
point
OSC coil
on RF
block M971
RF coil
on RF
block M971
L972 Maximum
1.35±0.2V
Maximum
1.3±0.2V (522kHz)
1.35±0.2V
(531kHz)
Maximum
Adjust
for
Adjust
for
- 10 -
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