Nad 7240 Service Manual

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SERVICE
MANUAL

STARTING SERIAL NUMBER A740l|0000|

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PAGE CONTENTS

3 REAR/FRONT PANEL LAYOUT
4 SPECIFICATIONS
5-8 ALIGNMENT METHOD
9 FM ALIGNMENT HOOKUP
IO TUNER ALIGNMENT POINTS
ll-IZ AMPLIFIER PCB LAYOUT
13-14 AMPLIFIER SCHEMATIC
IS-IS TUNER PCB LAYOUT
l7-l8 TUNER SCHEMATIC
19 TRANSFORMER WIRING (MULTI-VOLTAGE)
19-20 AMPLIFIER PCB WIRING DIAGRAM
21-22 TUNER PCB WIRING DIAGRAM
23 AMPLIFIER PCB PARTS LOCATION
24 TUNER PCB PARTS LOCATION
25 DISPLAY PCB SCHEMATIC, LAYOUT. PARTS LOCATION
26-31 ELECTRICAL PARTS LIST
32-33 EXPLODED VIEW
34-36 EXPLODED PARTS LIST-
37 PACKING DIAGRAM

SERVICE SAFETY PRECAUTIONS (UL)
I. Use exact replacement parts for critical locations, marked A
2. Return lead dress to original position, and re-install protective covers.
3. Before returning to customer, test for shock hazard; use either method A or B:
A. Leakage test, "cold":
I. Unplug AC cord; turn power switch ON;
2. Connect one lead of High Voltage Insulation Tester to both prongs of AC plug.
3. Touch other lead to all exposed metal parts.
4. Impedance measurement must be 0.3 - 5.0 Megohms.
B. Leakage. test. "live:
1. Plug unit directly into AC outlet; do not use isolation transformer.
2. Connect one lead of Leakage Current Tester to earth ground.
3. Touch other lead to all exposed metal parts.
4. Leakage measurement must be less than 0.5 milliamps.

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FM ALIGNMENT

NECESSARY INSTRUMENTATION:

Stereo Modulator (less than 0.05% THD. more than 50dB Sep.)
FM Generator (less than 0.05% THD)

300 or 75 ohm Dummy Antenna (if needed by generator)

Audio OSCIIlator (not necessary if FM Generator has built-in sweep, e.g.,
SOUND TECHNOLOGY ST 1000A or ST 1020A)

2 AC VTVM's (or one with a Left/Right switch)

THD Analyzer (resolution less than 0.1 %)

Oscilloscope (5mV or better sensitivity, X~Y capability)
Frequency Counter

DMM or DVM

Diode Detector Probe

Ferrite/Brass inductor test probe

IMPORTANT NOTES

RF levels are at 300 ohm antenna input. If using 75 ohm input, divide
figures by 2.

Before aligning, select FM and switch oft MONO (out) and FM NR (in).
if FM Generator is not synthesizer-type. be sure to check its frequency
with Frequency Counter when adjusting detector and stereo

decoder circuits.

Hum in measurements may be caused by ground loop via antenna cable:
if so, use isolation balun, or isolate antenna input with small
capacitors (470~1000pt).

To adjust front»end coils, bend gently with wooden or plastic tool
(non-interactive).

ENTER the following frequencies: 87.50, 90.00, 98.00, 105.00. 108.00

LOCAL OSCILLATOR FREQUENCY

1. Connect Frequency Counter between front-end pin 8 (front-most)
and Ground.

2. Tune to 90 MHz (No RF input needed).

3. Adjust VC-2 so that reading is 100.700MHz i 2kHz.

4. Remove counter.

TUNING VOLTAGE

. Connect DVM between R~96 (Front Lead) and Ground.

. Tune to 108.00MH2, and adjust L-702 it reading is not 20.5V : 0.5V.
. Tune to 87.50MHZ, and check that reading is 3.0V 1 0.5V.

. Repeat 2,3 until within tolerance.

. Remove DVM

(JIAQN-e

TRACKING

1. Connect FM Generatorto antenna input (modulate :150kHz sweep) (300 kHz
total)and Detector Probe to Pin 1 of Detector IC-3 (ground to front-end shield).
2. Adjust vertical sensitivity of Oscilloscope to maximum, and set to
X-Y mode. (X input is sweep signal, Y is detector probe).
3. Tune to 105MHz and adjust generator so that curve appears on
Oscilloscope, and covers approximately 1/2 of display.
4, Check L702, L704, L705 with ferrite/brass probe. adjust only it probe
causes curve height to increase more than 10%. If necessary, reduce
generator output to keep entire curve on display.
5. Tune to SOMHz and adjust Generator so that curve appears on
Oscilloscope.
6. Check L702, L704, L705 again; if necessary, distribute any error between
both frequencies.
Note: 105MHz curve is typically slightly higher than 90MHz.

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