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M27 SERVICE MANUAL
SEVEN CHANEL
AMPLIFIER

SEVEN
CHANEL
AMPLIFIER
M27
NAD
TABLE OF CONTENTS

DESCRIPTION PAGE

SERVICE CAUTION......................................................................3-4

SPECIFICATIONS...................................................................... 5

WIRING DIAGRAM..........................................................................6

BLOCK DIAGRAM.............................................................. ..........7-9

TROUBLE SHOOTING A GUIDE...........................................................10

TROUBLE SHOOTING B GUIDE...........................................................11

CIRCUIT DIAGRAMS .................................................................12-25

PCB LAYOUT..........................................................................26-33

ELECTRICAL PARTS LIST......................................................34-59

EXPLODED VIEW................................................................... 60-63

EXPLODED VIEW PARTS LIST.......................................................64
PRODUCT SAFETY SERVICING GUIDELINES FOR AUDIO PRODUCTS
CAUTION : DO NOT ATTEMPT TO MODIFY THIS 5. NO LEAD OR COMPONENT SHOULD TOUCH A
PRODUCT IN ANY WAY, NEVER PERFORM CUSTOM- RECIVING TUBE OR A RESISTOR RATED AT 1 WATT
IZED INSTALLATIONS WITHOUT MANUFACTURER'S OR MORE. LEAD TENSION AROUND PROTRUNING
APPROVAL. UNAUTHORIZED MODIFICATIONS WILL METAL SURFACES MUST BE AVOIDED.
NOT ONLY VOID THE WARRANTY, BUT MAY LEAD TO
6. ALL CRITICAL COMPONENTS SUCH AS FUSES,
YOUR BEING LIABLE FOR ANY RESULTING PROP-
FLAMEPROOF RESISTORS, CAPACITORS, ETC.
ERTY DAMAGE OR USER INJURY.
MUST BE REPLACED WITH EXACT FACTORY TYPES,
SERVICE WORK SHOULD BE PERFORMED ONLY DO NOT USE REPLACEMENT COMPONENTS OTHER
AFTER YOU ARE THOROUGHLY FAMILIAR WITH ALL THAN THOSE SPECIFIED OR MAKE UNRECOM-
OF THE FOLLOWING SAFETY CHECKS AND SERVIC- MENDED CIRCUIT MODIFICATIONS.
ING GUIDELINES. TO DO OTHERWISE,INCREASES
7. AFTER RE-ASSEMBLY OF THE SET ALWAYS PER-
THE RISK OF POTENTIAL HAZARDS AND INJURY TO
FORM AN A.C. LEAKAGE TEST ON ALL EXPOSED
THE USER.
METALLIC PARTS OF THE CABINET, (THE CHANNEL
WHILE SERVICING, USE AN ISOLATION TRANS- SELECTOR KNOB, ANTENNA TERMINALS. HANDLE
FORMER FOR PROTECTION FROM A.C. LINESHOCK. AND SCREWS) TO BE SURE THE SET IS SAFE TO
OPERATE WITHOUT DANGER OF ELECTRICAL
SAFETY CHECKS SHOCK. DO NOT USE A LINE ISOLATION TRANS-
AFTER THE ORIGINAL SERVICE PROBLEM HAS FORMER DURING THIS TEST USE AN A.C. VOLTME-
BEEN CORRCTED. A CHECK SHOULD BE MADE OF TER, HAVING 5000 OHMS PER VOLT OR MORE SEN-
THE FOLLOWING. SITIVITY, IN THE FOLLOWING MANNER; CONNECT A
1500 OHM 10 WATT RESISTOR, PARALLELED BY A
SUBJECT : FIRE & SHOCK HAZARD .15 MFD. 150.V A.C TYPE CAPACITOR BETWEEN A
1.BE SURE THAT ALL COMPONENTS ARE POSI- KNOWN GOOD EARTH GROUND (WATER PIPE,
TIONED IN SUCH A WAY AS TO AVOID POSSIBILITY CONDUIT,ETC.) AND THE EXPOSED METALLIC
OF ADJACENT COMPONENT SHORTS.THIS IS ESPE- PARTS, ONE AT A TIME. MEASURE THE A.C. VOLT-
CIALLY IMPORTANT ON THOSE MODULES WHICH AGE ACROSS THE COMBINATION OF 1500OHM
ARE TRANSPORTED TO AND FROM THE REPAIR RESISTOR AND .15 MFD CAPACITOR. REVERSE THE
SHOP. A.C. PLUG AND REPEAT A.C. VOLTAGE MEASURE-
2. NEVER RELEASE A REPAIR UNLESS ALL PROTEC- MENTS FOR EACH EXPOSED METALLIC PART. VOLT-
TIVE DEVICES SUCH AS INSULATORS, BARRIERS, AGE MEASURED MUST NOT EXCEED 75 VOLTS
COVERS, SHIELDS, STRAIN RELIEFS, POWER R.M.S. THIS CORRESPONDS TO 0.5 MILLIAMP A.C
SUPPLY CORDS, AND OTHER HARDWARE HAVE- ANY VALUE EXCEEDING THIS LIMIT CONSTITUTES A
BEEN REINSTALLED PER ORIGINAL DESIGN. BE POTENTIAL SHOCK HAZARD AND MUST BE COR-
SURE THAT THE SAFETY PURPOSE OF THE POLAR- RECTED IMMEDIATELY.
IZED LINE PLUG HAS NOT BEEN DEFEATED.
3. SOLDERING MUST BE INSPECTED TO DISCOVER A.C. VOLTMETER
POSSIBLE COLD SOLDER JOINTS, SOLDER
SPLASHES OR SHARP SOLDER POINTS. BE CER-
TAIN TO REMOVE ALL LOOSE FOREIGN PARTICLES.
4. CHECK FOR PHYSICAL EVIDENCE OF DAMAGE
OR DETERIORATION TO PARTS AND COMPONENTS. GOOD EARTH GROUND PLACE THIS PROBE
SUCH AS THE WATER ON EACH EXPOSED
FOR FRAYED LEADS, DAMAGED INSULATION PIPE. CONDUIT. ETC METAL PART
(INCLUDING A.C. CORD). AND REPLACE IF NECES-

SUBJECT: GRAPHIC SYMBOLS
THE LIGHTNING FLASH WITH APROWHEAD SYMBOL. WITHIN AN EQUILATERAL TRIANGLE, IS INTENDED
TO ALERT THE SERVICE PERSONNEL TO THE PRESENCE OF UNINSULATED "DANGEROUS VOLTAGE"
THAT MAY BE OF SUFFICIENT MAGNITUDE TO CONSTITUTE A RISK OF ELECTRIC SHOCK.
THE EXCLAMATION POINT WITHIN AN EQUILATERAL TRIANGLE IS INTENDED TO ALERT THE SERVICE
PERSONNEL TO THE PRESENCE OF IMPORTANT SAFETY INFORMATION IN SERVICE LITERATURE.

3
SERVICING PRECAUTIONS

CAUTION: Before servicing the Stereo amplifier covered by Electrostatically Sensitive (ES) Devices
this service data and its supplements and addends, read and Some semiconductor (solid state) devices can be damaged
follow the SAFETY PRECAUTIONS. NOTE: if unforeseen easily by static electricity. Such components commonly are
circumstances create conflict between the following servicing called Electrostatically Sensitive (ES) Devices. Examples of
precautions and any of the safety precautions in this publication, typical Es devices are integrated circuits and some field effect
always follow the safety precautions. transistors and semiconductor chip components.
Remember Safety First: The following techniques should be used to help reduce the
incidence of component damage caused by static electricity.
General Servicing Precautions
1. Always unplug the Stereo amplifier AC power cord from the 1. Immediately before handing any semiconductor component
AC power source before: or semiconductor-equipped assembly, drain off any
(1) Removing or reinstalling any component, circuit board, electrostatic charge on your body by touching a known earth
module, or any other assembly. ground. Alternatively, obtain and wear a commercially
(2) Disconnecting or reconnecting any internal electrical available discharging wrist strap device, which should be
plug or other electrical connection. removed for potential shock reason prior to applying power to
(3) Connecting a test substitute in parallel with an electrolytic the unit under test.
capacitor.
Caution: A wrong part substitute or incorrect polarity 2. After removing an electrical assembly equipped with ES
installation of electrolytic capacitors may result in an devices, place the assembly on a conductive surface such as
explosion hazard. aluminum foil, to prevent electrostatic charge buildup or
exposure of the assembly.
2. Do not spray chemicals on or near this Stereo amplifier or
any of its assemblies. 3. Use only a grounded-tip soldering iron to solder or unsolder
ES devices.
3. Unless specified otherwise in this service data, clean
electrical contacts by applying an appropriate contact 4. Use only an antistatic solder removal device. Some solder
cleaning solution to the contacts with a pipe cleaner, removal devices not classified a "anti-static" can generate
cottontipped s wab, or comparable soft applicator. electrical charges sufficient to damage ES devices.
Unless specified otherwise in this service data, lubrication
of contacts is not required. 5. Do not use freonpropelled chemicals. These can generate
electrical charge sufficient to damage ES devices.
4. Do not defeat any plug/socket B+ voltage interlocks with
which instruments covered by this service manual might be 6. Do not remove a replacement ES device from its protective
equipped. package until immediately before you are ready to install it.
(Most replacement ES devices are packaged with leads
5. Do not apply AC power to this Stereo amplifier and/or any electrically shorted together by conductive foam, aluminum
of its electrical assemblies unless all solid-state device heat foil, or comparable conductive material).
sinks are correctly installed.
7. Immediately before removing the protective material from the
6. Always connect test instrument ground lead to the leads of a replacement ES device, touch the protective
appropriate ground before connecting the test instrument material to the chassis or circuit assembly into which the
positive lead. Always remove the test instrument ground lead device will be installed.
last.
Caution: Be sure no power is applied to the chassis or circuit,
Insulation Checking Procedure and observe all other safety precautions.
Disconnect the attachment plug from the AC outlet and turn the
power on. Connect an insulation resistance meter (500V) to the 8.Minimize bodily motions when handing unpackaged
blades of the attachment plug. The insulation resistance replacement ES devices. (Normally harmless motion such as
between each blade of the attachment plug and accessible the brushing together of your clothes fabric or the lifting of
conductive parts (Note 1) should be more than 1 M-ohm. your foot from a carpeted floor can generate static electricity
Note 1: Accessible Conductive Parts including Metal panels, sufficient to damage an ES device.)
Input terminals, Earphone jacks, etc.

4
SPECIFICATIONS

M27
Continuous output power into 8 and 4 180W (ref. rated THD, 20Hz-20kHz, all channels driven)
THD +N (250mW to rated power, CCIF IMD, DIM 100) 0.005% (ref. 20Hz - 20kHz)
IHF Dynamic Power 8 Ohms 320W
4 Ohms 700W
2 Ohms 650W
FRAN