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S250 SERVICE MANUAL
FIVE CHANNEL
POWER AMPLIFIER




FIVE CHANNEL
POWER AMPLIFIER
S250
CONTENTS

FRONT PANEL / REAR PANEL VIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
ALIGNMENT PROCEDURE / ALIGNMENT POINTS . . . . . . . . . . . . . . . . . . . . . . . . 5
WIRING DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
PCB LAYOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-8
SCHEMATIC DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-11
ELECTRICAL PARTS LIST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-14
EXPLODED VIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
EXPLODED VIEW PARTS LIST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
PACKING DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17


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
PSU Board
F1*AH ! 5120-0506-0 12.5A 250V Time Lag 6.3x32mm UR

F1*C ! 5120-0025-0 6.3A 250V HBC Time Lag 5x20mm SEMKO/VDE


Amp Board
F1-F2*AH ! 5120-0040-0 6.3A 250V Time Lag 5x20mm UL

F1-F2*C ! 5120-0025-0 6.3A 250V HBC Time Lag 5x20mm SEMKO/VDE

NOTE:
*AH : North American version only
*C : European version only



2. Safety-check out (North American model only)
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.
FRONT PANEL / REAR PANEL VIEW RETURN TO CONTENTS
FRONT PANEL CONTROLS

NAD Five Channel Power Amplifier S250




PROTECTION SOFT CLIPPING




1 2 3 4

1. POWER SWITCH 3. PROTECTION INDICATOR
2. POWER INDICATOR 4. SOFT CLIPPING INDICATOR

The graphic symbol of a lightning flash with an arrow point The graphic symbol of an exclamation point within
within a triangle signifies that there is dangerous voltage an equilateral triangle warns a user of the device
within the unit and it posses a hazard to anyone removing that it is necessary to refer to the instruction
the cover to gain access to the interior of the unit. Only manual and its warnings for proper operation of
qualified service personnel should make such attempt. the unit.



REAR PANEL CONNECTIONS
1 2 345




1
AUTO TRIGGER




+12V TRIGGER IN




AC MAINS INPUT
120V




6 7
1. LEVEL CONTROL 5. 12V TRIGGER INPUT
2. INPUT JACK 6. SPEAKER TERMINALS
3. SOFT CLIPPING SWITCH 7. AC INLET
4. AUTO TRIGGER SWITCH
RETURN TO CONTENTS
SPECIFICATIONS

Specifications are measured in accordance with IHF standard IHF-A-202, 1978.



NOMINAL LIMIT

1. THD #0.02% #0.03%



2. Continuous Power Output 8 ohms $125W $100W
20kHz, 5 ch. for 8 ohms, 4 ch. for 4 ohms) 4 ohms $125W $100W



3. Clipping Power $135W $110W



4. S/N Ratio A-wtd $96dB $93dB
maximum) Audio BPF $89dB $86dB



5. Frequency Response 0 ~ -0.1dB 0 ~ -0.25dB



6. Input Sensitivity 100