Nad C-426 Service Manual
NAD
SERVICE MANUAL
C 426
STEREO
C 426
STEREO
AM/FM TUNER
AM/FM TUNER
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 ............................................................3-4
REAR PANEL / FRONT PANEL . ................................................. 5
DISASSEMBLY INSTRUCTIONS ................................................. 6
BLOCK DIAGRAM . ........................................................... 7
WIRING DIAGRAM ............................................................ 8
ADJUSTMENT POINTS DIAGRAM . .............................................. 9
INSTRUMENT SETUP . ....................................................... 10
ALIGNMENT PROCEDURES ....................................................11
PCB LAYOUT . ............................................................12-14
SCHEMATIC DIAGRAM . ....................................................15-17
IC BLOCK DIAGRAM . ......................................................18-22
ELECTRICAL PARTS LIST ...................................................23-31
EXPLODED VIEW ............................................................ 32
EXPLODED VIEW PARTS LIST ................................................. 33
PACKING DIAGRAM .......................................................... 34
- 2 -
SPECIFICATIONS
AM BAND SPECIFICATION
Frequency Range CA 530 - 1710 KHz Step 10 KHz
EU 531 - 1602 KHz Step 9 KHz
FREQ (KHz) UNIT LIMIT
1. Usable sensitivity 999 dBuV <= 30
(400Hz, -20dB, direct input) /1000
2. S/N RATIO 999 dB >= 38
(5mV input) /1000
3. THD (5mV input) 999 % <= 3
/1000
4. IF Rejection (450KHz) 603 dB >= 36
(ref. to item 8) /600
5. Image Rejection (F+2xIF) 1404 dB >= 25
(ref. to item 8) /1400
6. Selectivity 999 dB >= 17
(ref. to item 8) /1000
7. Output 999 mV 100 ~ 180
(30%, 10mV) /1000
8. Loop sensitivity 20dB S/N 999/1000 dB <= 68
603 / 600 dB <= 68
1404 / 1400 dB <= 68
9. Frequency response 100 - 2.3KHz 999 /1000 dB 0 +/- 6dB
(400 Hz, 5mV)
FM BAND SPECIFICATION
Frequency Range CA/EU 87.5 - 108MHz Step 50 KHz
FREQ UNIT LIMIT
1. Usable sensitivity MONO 98MHz dBu <= 15
IHF (3% THD)
2. S/N RATIO
(60dBu A filter) MONO 98MHz dB >= 72
(60dBu A filter) STEREO 98MHz dB >= 68
3. THD (60dBu Audio LPF) MONO 98MHz % < 0.4
(60dBu Audio LPF) STEREO 98MHz % < 0.6
L = R, C=40KHz Dev.
4. IF Rejection (10.7MHz) CA&EU 98MHz dB > 80
(refer to item 1)
5. Image Rejection (119.4 MHz) CA&EU 98MHz dB >= 70
(refer to item 1)
- 3 -
6. Capture ratio (40dBu) dB < 3
7. AM Supression 98MHz dB > 60
@ 60dBu 100% mod FM, 30% mod AM
8. Pilot suppression L & R 98 MHz dB > 60
9. Frequency response 20Hz & 10KHz dB 0 +/- 1.5
( 1KHz Ref ) UL 75Us,CE50Us
10. Channel Separation @ 30 Hz dB >= 28
(60dBu IHF wtd) 1 KHz dB >= 38
10KHz dB >= 28
11. Alternate channel selectivity +/-400KHz, IHF UL dB >= 35
CE dB > 60
12. Muting level dBu 18 +/-6.
13. Output CA 98MHz mV 350~600
EU 550~900
14. RDS decode sensitivity. dBu <= 30
15. Auto-search sensitivity ON dBu <= 30
OFF dBu >= 15
16. Blend ON separation@1KHz 98MHz dB 6 +/-2
- 4 -
REAR PANEL / FRONT PANEL
REAR PANEL
143256 7
1. FM ANTENNA TERMINAL
2. AM ANTENNA TERMINAL
3. OUTPUT (L, R)
4. RS-232
FRONT PANEL
12 3456789 10 11
1. STANDBY LED
2. STANDBY BUTTON
3. FM/AM
4. FM MUTE/MODE
5. BLEND
6. DISPLAY
5. IR IN
6. +12V TRIGGER IN
7. AC MAINS INPUT
7. MEMORY
8. PRESET/TUNE
9. REMOTE SENSOR
10. VFD
11. PRESET/TUNE CONTROL KNOB:
IMPORTANT NOTES
1. Show the software version
Press “DISPLAY” and “FM/AM”.
2. Light UP all the icon on the VFD
Press “FM/AM” & “PRESET/TUNE”.
3. Factory test resets
When VFD all Light press any key.
4. AM Step 10K/9K Change
When AM band, press “FM MUTE/MODE” & “PRESET/TUNE”.
5. Shipment resets (clear)
When pressing “MEMORY” & “PRESET/TUNE” to VFD all Light, press any key.
- 5 -
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.
4
3
5
2
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.
6
Figure No.2.
- 6 -
7
6
BLOCK DIAGRAM
L
R
OUTPUT
MUTING
17
16
23
AC INPUT
RELAY
IR IN
RS232
2
MPXIN
U701
74HC86
POWER
STANDBY
STANDBY 3V3
SUPPLY
VFD
POWER
SUPPLY
-VP
+10V
+5V CPU
U901
AM/FM IF
27
FM ANT
LA1837
30
1
FRONT END
VT
ENV172D3G1
U902
LC72723M
TUNE
ST/MO, MUTE, SMETER
AM
OSC/IF
LC7218
FM
OSC/IF
19 18
PLL
VT
21
16 14
RDS DECODER
data
out
U903
ce data clk RDS-CLK RDS-SIG RDS-DATA
2345 15
16 19 24
20
11
8
15
CPU
P89LPC936
16
14
22
U201
10 IN
12/13
U202
PT6311
VFD DRIVER
(#1)=Power On
(#2)=Standby
M218
REMOTE
VFD
5
SENSOR
AM LOOP ANT
KEY MATRIX
- 7 -
Trigger IN
U203
24C08
EEPROM
WIRING DIAGRAM
KEY board
MAIN board
TRANSFORMER
PSU board
BLUE
YELLOW
WHITE
7013-0490+0
DSP board
LED board
- 8 -
ADJUSTMENT POINTS DIAGRAM
VT
OSC RF
- 9 -
INSTRUMENT SETUP
1. FM MEASUREMENT
Fig. 1
FM
SIGNAL
GENERATOR
ANTENNA
TERMINAL
UNIT
OUTPUT
TERMINAL
P901
DC
MILLIVOLT-
METER
OUTPUT
TERMINAL
DISTORTION
METER
AC
VOLTMETER
OR
OSCILLOSCOPE
Fig. 2
FM
STEREO
GENERATOR
2. RDS MEASUREMENT
Fig. 3
RDS
GENERATOR
3. AM MEASUREMENT
Fig. 4
AM
SIGNAL
GENERATOR
FM
SIGNAL
GENERATOR
FM
SIGNAL
GENERATOR
AM LOOP
ANTENNA
ANTENNA
TERMINAL
ANTENNA
TERMINAL
60cm
AM LOOP
ANTENNA
(Accessory)
UNIT
OSCILLOSCOPE
UNIT
ANTENNA
TERMINAL
OUTPUT
TERMINAL
L
R
UNIT
VT_J911
DISTORTION
METER
AC
VOLTMETER
OUTPUT
TERMINAL
AC
VOLTMETER
OR
OSCILLOSCOPE
- 10 -
DIGITAL
MILLIVOLT-
METER
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
- 11 -
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