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MC 250
SERVICE INFORMATION
S T A R T I N G WITH S E R I A L N O . 23L48
MCINTOSH LABORATORY INC.
2 CHAMBERS STREET
BINGHAMTON, NEW YORK
MC 250
ELECTRICAL SPECIFICATIONS
Power Output: 100 watts RMS continuous, 50 watts per channel operating simultaneously, into 4 ohm, 8 ohm, or 16 ohm loads. Harmonic Distortion: Less than 0.25% at rated power output from 20Hz to 20,000Hz. Intermodulation Distortion: Less than 0.25% for any combination of frequencies between 20 Hz and 20,000 Hz. Frequency Range: At rated output both channels: through 20,000Hz. Output Damping Factor: Greater than 10 for any output tap. Input Sensitivity & Impedance: Input sensitivity is 0.5 volts. Hum & Noise : Greater than 90dB below rated output. Power Requirements: 117 volts AC,50-60Hz, 50 watts at zero signal output, 250 watts at rated output. Input impedance Is 200K ohms. +0 to -0.25dB from 20Hz
MC 250
MC 250
LEFT CHANNEL POWER OUTPUT PRINTED CIRCUIT BOARD 043-916
RIGHT CHANNEL POWER OUTPUT PRINTED CIRCUIT BOARD 043-916
INPUT
SECTION
PRINTED
CIRCUIT
BOARD 043-795
MC 250
MC 250
MC 250
SCHEMATIC NOTES 1. Unless otherwise s p e c i f i e d : R e s i s t a n c e v a l u e s are i n ohms, 1 / 2 w a t t , and 10% t o l e r a n c e ; c a p a c i t a n c e v a l u e s s m a l l e r than 1 are i n m i c r o f a r a d s ( µ F ) ; c a p a c i t a n c e v a l u e s g r e a t e r than 1 a r e i n p i c o f a r a d s ( p F ) ; i n d u c t o r s are i n mi c rohen r i es ( µ H ) . P r i n t e d c i r c u i t board components are o u t l i n e d o n t h e s c h e m a t i c s b y dotted lines. The c i r c l e d numbers on the d o t t e d l i n e s c o r r e s p o n d to the numbers on the PC Board l a y o u t s . The heavy l i n e s on the s c h e m a t i c s denote the p r i m a r y s i g n a l A l l voltages conditions : a. b. c. d. e. path.
2.
3. 4.
i n d i c a t e d o n the s c h e m a t i c s a r e measured under the f o l l o w i n g megohm impedance V T V M .
Use of an 11
A l l v o l t a g e s ± 1 0 % w i t h r e s p e c t t o c h a s s i s ground. No s i g n a l at input t e r m i n a l s .
A C input a t 1 1 7 v o l t s , 50/60Hz. Front panel Left Gain Right Gain Mode controls at: F u l l y CCW F u l l y CCW Stereo
5. 6.
I n u n i t s w i t h S e r i a l N o . ' s b e l o w 2 8 L 2 1 : R88, R89, R90 & R 9 1 are used; R49 & R50 are 2200W; R86 & R87 are 160W; and R 3 3 & R34 are 3 3 k . I n u n i t s w i t h S e r i a l N o . ' s from 28L60 t o 3 7 L 7 5 , C 5 & C 6 a r e 180pF.
Q21 BOTTOM
Q25 TOP
Q19 BOTTOM
Q23 TOP
Q26 TOP
Q22 BOTTOM
Q24 TOP
Q20 BOTTOM
L O C A T I O N O F T R A N S I S T O R S NOT O N P R I N T E D C I R C U I T B O A R D S
MC 250
R E P L A C E M E N T PARTS
All parts not listed are common items o b t a i n able from radio parts jobbers . Rep1acement parts may be o b t a i n e d when ordered by PART NUMBER from: Mclntosh Laboratory Inc. Customer Service Department 2 Chambers Street Binghamton, New York 13903 (telephone 607 723-3512) CAPACITORS Symbol Number Description Elect. Elect. Elect. Mylar Elect. Elect. Elect. Elect.
470µF 4V
Q23,24 Q25,26
S i . NPN t r a n s i s t o r S i . NPN t r a n s i s t o r POTENTIOMETERS
132-070 132-070
Rl R2
Left g a i n Right/mono g a i n RESISTORS
134-206 134-206
R43,44 R57,58 Part Number 066-136
Wirewound Wirewound Wirewound
3.6k .56W .33W
5W 5W 5W
139-065 139-048 139-071
R59,60
Cl1 , 12
C27,28
SWITCHES
9300µF
45V
066-106
066-095
S1 ,2 S3
Thermal cut out Modeselector TRANSFORMERS
153-007 153-008
C29
C47,48
80/80/1 50/50µF 200/200/150/150V .47µF 100µF
10µF
064-045
15V
25V
C51 ,52
066-127 066-005 066-157 066-137
Tl T2 T3
Power transformer Output transformer (right) Output transformer (left) M I S C E L L A N E O U S ITEMS
043-605 043-667 043-668
C53,54 C55,56
C57
640µF 500µF DIODES
25V 50V
P l a s t i c feet
017-040 038-287 knob 090-017 033-077 170-021
D1 ,2
reference diode
070-046
070-022 070-022 070-O4
Owners m a n u a l G a i n control
D5,6 07,8
D13,14
si.
r e c t i f i e r diode
Si . r e c t i f i e r diode Si . r e c t i f i e r diode
rectifier d i o d e
S h i p p i n g carton AC power cord
D15,16
D18
D20
Si . r e c t i f i e r diode Si . r e c t i f i e r diode Si . r e c t i f i e r d i o d e Si . r e c t i f i e r diode Si . r e c t i f i e r diode
FUSES
D25,26 D27,28
070-041 070-031 070-031 070-031 070-031
070-022
D31 ,32
Fl
2.5A c i r c u i t breaker
TRANSISTORS
088-001
Q1 ,2
S i . NPN transistor
Si . NPN transistor
132-054 132-054 132-056 132-056 132-056 132-515 132-021 132-032 132-524 132-530
15C01047S-M1508
Q3, 4
Q5,6 Q7,8
si.
PNP t r a n s i s t o r
Si . PNP t r a n s i s t o r Si . PNP t r a n s i s t o r
Q9.10
Q11 ,12
S i . NPN transistor
Si . NPN t r a n s i s t o r Si . PNP t r a n s i s t o r
Q15,16 Q17,18
Q19,20
Si.
NPN transistor
Q21 ,22
Si . PNP transistor
SCHEMATIC PART NO. 038-508