McIntosh C26 Preamp Service Information.pdf

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1、HMntosh C 26 PREAMPLIFIER SERVICE INFORMATION STARTING WITH SERIAL NO. 10P01 r _ o MclNTOSH LABORATORY INC. 2 CHAMBERS STREET BINGHAMTON, NEW YORK hO o C 26 ELECTRICAL SPECIFICATIONS FREQUENCY RESPONSE +0 to -0.5dB from 20Hz to 20,000Hz DISTORTION Less than 0.1$ at 2.5 volts output, 20Hz to 20,000Hz

2、 INPUT SENSITIVITY (phono 1 and phono 2) 2 millivolts for 2.5 volts output at 1kHz INPUT SENSITIVITY (aux, tape 1, tape 2, tuner) 0.25 volts for 2.5 volts output HUM AND NOISE (phono 1 and phono 2) 7l4-dB below rated output for a 10 millivolt input signal HUM AND NOISE (aux, tape 1, tape 2, tuner) 8

3、5dB below rated output OUTPUT (main) 2.5 volts with rated input. Up to 10 volts can be developed without distortion. OUTPUT (tape) 0.25 volts with rated input. Phono input sig nal of 10 millivolts produces 1.2 volts output. OUTPUT (center channel) 2.5 volts with rated input on both channels. A level

4、 control adjusts output from -6dB to +6dB with respect to main output. BASS CONTROL -20dB to +l6dB at 20Hz TREBLE CONTROL +20dB at 20,000Hz LF FILTER Flat or roll off below 50Hz, down 12dB at 20Hz HF FILTER Flat or roll of above 5000Hz, down 12dB at 20,000Hz C 26 SCHEMATIC NOTES 1. Unless otherwise

5、specified; Resistance values are in ohms, 1/4 watts, and 10% tolerance; capacitance values smaller than 1 are in microfarads (pF); capacitance values greater than 1 are in picofarads (pF); inductors are in microhenries (pH). 2. Printed circuit board components are outlined on the schematics by dotte

6、d lines. The circled numbers around the dotted lines correspond to the numbers on the PC Board layouts. 3. The heavy lines on the schematics denote the primary signal path. 4. The terminal numbering of rotary switches is for reference only. 5. All voltages indicated on the schematics are measured un

7、der the following conditions: a. Use of an 11 megohm input impedance VTVM. b. All voltages 10% with respect to chassis ground. c. No signal at input terminals. d. AC input at 117 volts, 50/60HZ. e. Front panel controls at: Volume Fully CCW, but with power switch on Mode Stereo Input Selector Phono 1

8、 Loudness Flat All other controls at normal positions. 6. R313 is IK in early units. 7. In units with serial Nos below 30P55, C309 and C310 are not used. 8. In units with serial Nos below 30P50, R127 and R128 are not used. 9. In units with serial Nos below 30P53, R129 and R130 are not used. 10. In u

9、nits with serial Nos below AG3301; C3, C4, C13 S- C14 are used; C48, C49, C50, C51, C52 C53, R131 R132 are not used; R129 R25 & R26 are 1,8k. 5 PRINTED CIRCUIT BOARD CENTER CHANNEL 043-789 POWER SUPPLY 2 2 COAX COAX RIGHT CHANNEL PREAMP PRINTED CIRCUIT BOARD 044-553 R 21 LEFT CHANNEL INPUTS PH 2 PH

10、1 TUNER TAPE 1 TAPE 2 AUX TAPE 1 OUT O- TAPE 2 OUT O- o o- o- o- o- o- PH 2 O PH 1 o- RIGHT CHANNEL- TUNER o- INPUTS TAPE 1 o TAPE 2 o- AUX v_ o- TAPE 1 OUT o- TAPE 2 OUT o- R 22 LEFT CHANNEL PREAMP SECTION PRINTED CIRCUIT BOARD 044-554 LEFT I MAIN OUTPUT TO CENTER CHANNEL SECTION 24K I /24K * 5* VL

11、-IL1/ 5% R 87 R 83 IOOK 5% IOOK 5% R 85 R99 IOOK 5% IOOK 5% PREAMP SECTION c 26 154 - 656 R 88 R84 IOOK 5% IOOK 5% R 90 R 86 IOOK 5% IOOK 5% T C 38 R 62 .47 2.2K r | i i JL YEL/WHT mv?n 1 is) m 9 o MAIN | OUTPUT TO CENTER CHANNEL SECTION MODULE 130-027 SPEAKER SWITCHING SECTION C26 154-342 Q5,6 Q7,8

12、 Si. N PN t ransis tor C 26 REPLACEMENT PARTS All parts not listed are common items obtain able from radio parts jobbers. Replacement parts may be obtained when ordered by PART NUMBER from: McIntosh Laboratory, Inc. Customer Service Department 2 Chambers Street Binghamton, New York 13903 (telephone

13、607-723-3512) Symbo1 Numbe r CAPACITORS Description Part Number Cl , 2 Mylar 47 pF 250V 064-069 C5,6 El ect. 1 OpF 35 V 066-239 C7,8 Elect. 10pF 35V 066-239 C15,16 Elect. lOOpF 1 6 V 066-226 C17 .18 Mylar 47 pF 250V 064-069 C19.20 Mylar . 22 pF 200V 064-087 C21 ,22 My 1 a r .047 pF 250V 064-066 C23.

14、24 Mylar . 47pF 250V 064-069 C25 Mylar 47pF 250V 064-069 C26.27 Mylar .047 pF 250V 064-066 C28,29 Mylar .022 pF 250V 064-065 C34,35 Mylar .022pF 250V 064-064 C 36,37 Mylar . IpF 250V 064-067 C38.39 Myl ar 47 pF 250V 064-069 C44.45 Mylar .047 pF 250V 064-066 C46.47 Mylar . 47 pF 250V 064-069 C301 Myl

15、ar . 22pF 250V 064-068 C302 Mylar -47pF 250V 064-069 C304 El ect. 160/200pF 200/150V 066-095 C305 Elect. 160/200pF 200/150V 066-095 C306 Mylar . 22 pF 250 V 064-068 C307 El ect. lOOpF 16v 066-226 C308 Elect. lOOpF 16 v 066-227 D1 ODES D301,302 Si. rectifier 070-031 D303 Zener diode 75V 070-025 FUSES

16、 F301 Fuse 1/2 ampe re 089-009 TRANS 1STORS Q1 ,2 Si. PNP t ransistor 132-096 Q3,4 Si. PNP t ransistor 132-096 Q5,6 Si. NPN t ransis tor 132-095 Q7,8 Si. NPN transistor 132-095 Q9,10 Si. PN P t ransistor 132-096 Q11.12 Si. NPN t ransis tor 132-095 Q13.14 Si. NPN transistor 132-092 Q15,16 S i . NPN t

17、ransistor 132-042 Q301 S i . NPN transistor 132-095 Q302 S i . NPN transistor 1 32-028 POTENTIOMETERS R33 Volume control 134-200 R55 Loudness control 134-199 R56 Balance control 134-198 R304 Center channel level 134-196 RESISTORS R201,202 Wirewound 100n 10% 5W 139-008 R203.204 Wirewound 16a 10% 20W

18、139-022 SWITCHES SI Input selector switch 146-121 S2 Pushbutton switch 150-006 S3 Mode selector switch 146-122 S4 Phase control switch 146-1 19 S5 Bass switch 146-123 S6 Treble switch 146-123 S201,202 Speaker switch 148-025 TRANSFORMERS T 301 Power transformer 043-786 MODULES Tone control 130-027 LA

19、MPS #1866 (front panel) 058-014 FRONT PANEL AND TRIM Front panel 043-784 Front panel end caps 018-120 Volume control knob 044-372 Balance control knob 044-372 Loudness control knob 044-372 Mode selector knob 044-372 Input selector knob 044-372 Treble knob (rear) 090-009 Treble knob (front) 044-374 B

20、ass knob (rear) 090-009 Bass knob (front) 044-374 Phase knob 044-373 Center channel knob 044-373 Plastic Pushbutton 017128 MOUNTING SYSTEM Shelf bracket (right) Shelf bracket (left) Mounting template #100 Hardware package 170-021 178-001 043-946 038-867 017-041 127-001 074-030 170-015 15C0407S 7-M69

21、64 MISCELLANEOUS ITEMS Line cord Fuseholder Shipping carton Owners manual Plastic feet Shorting p1ug Push terminal (outputs) Audio cab 1e (6 1 ) 043-592 043-593 038-179 043-792 C 26 SCHEMATIC PART NO. 038-964 SERVICE BULLETIN C 26 S B No. 1 LOW FREQUENCY FILTER SWITCH MODIFICATION MODEL: C 26 Preamp

22、 PURPOSE OF MODIFICATION: To eliminate a popping sound when the low frequency filter switch is dep ressed. WHAT UNITS ARE AFFECTED: Serial No. 10P01 to 30P52 Only. WHEN MODIFICATION SHOULD BE MADE: When the customer specifically mentions the noise or when any other service is performed on the unit.

23、MclNTOSH MODIFICATION KIT no.: No kit available. PARTS REQUIRED: Quantity Part Number Description 2 136-236 1 meg, 10%, 1/2W Resistor PROCEDURE: Step 1 Remove bottom cover. Step 2 Add 1 resistor to the bottom side of each PC board as shown. The parts appear as R129 and R130 on the drawing. (over) 03

24、 f* McIntosh Laboratory Incorporated 2 Chambers Street Binghamton, New York 13903 Phone: Area Code 607-723-3512 No.l C 26 S.B. No. 2 SERVICE BULLETIN REDUCE RF INTERFERENCE MODEL: C 26 Preamplifier PURPOSE OF MODIFICATION: To reduce sensitivity to RF-interference. WHAT UNITS ARE AFFECTED: All units

25、with Serial Numbers below AG3301 WHEN MODIFICATION SHOULD 8E MADE: Whenever a customer complains of undesired reception of CB and HAM-apparatus, when the unit is operating in the Phono Mode-also when interference from man-made noise is encountered, such as: Refridgerators, passing cars, etc. PARTS R

26、EQUIRED: QUANT!TY PART NUMBER DESCRIPTION 2 136301 Res. = 100K, 1/4W, 10% R399,400 2 061002 Disc. Cap. = 1.8pF, .25pF NP0 2 061008 Disc. Cap. = 6.8pF, 20% NP0 2 061032 Disc. Cap. = 470pF, 20% 2 136296 Res. = IK, 1/4W, 10% PROCEDURE: This change has to be made on 043091 and 043092. both left and righ

27、t PC board 1. Diseard : C302, C313, R399, 304 = 061010 314 = 061009 400 = 136303 = Disc. Cap. 12pF = Disc. Cap. lOpF = Comp. Res. 1M 2. Connect a 061032 = 470pF capacitor between the base and the emitter of transistor Q301, 302. 00 CO o 2 NJ 0 (T (OVER) (VJ McIntosh Laboratory Incorporated 2 Chamber

28、s Street Binghamton, New York 13903 Phone: Area Code 607-723-3512 3. Connect a 061002 = 1.8pF capacitor from the collector of transistor Q301, 302 to the collector of transistor Q305, 306. 4. Connect a 061008 = 6.8pF capacitor from the base of transistor Q307, 308 to the collector of transistor Q307

29、, 308. 5. Replace R399 (R400) with a 136301 = 100K resistor. 6. Add a 1000 ohm resistor (136296) in series with the blue lead that connects to pin #10 on the left preamp board. This resistor should connect directly to pin #10 and the end of the blue lead. Using leads no longer than necessary, do the same for the blue/white lead connecting to pin #7 on the right preamp board. 039-036