McIntosh MX112 Tuner-Preamp Service Information Early Production.pdf

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1、nWntosb MX 112 FM/AM TUNER PREAMP SERVICE INFORMATION FROM SERIAL NO. 10S01 TO 39S99 MclNTOSH LABORATORY INC. 2 CHAMBERS STREET BINGHAMTON, NEW YORK MX 112 1 * a I ! C ELECTRICAL SPECIFICATIONS FM TUNER SECTION PREAMPLIFIER SECTION USABLE SENSITIVITY Better than 2.5pF (IHF usable sensiti vity) SIGNA

2、L TO NOISE RATIO Better than 65dB HARMONIC DISTORTION Mono, less than 0.5%- Stereo, less than 0.8%. FREQUENCY RESPONSE Flat from 20Hz to 20kHz with standard de-emphasis and 19kHz pilot filter CAPTURE RATIO Better than 1.5dB SPURIOUS REJECTION 90dB or greater IMAGE REJECTION 75UB or greater (at 100MH

3、z) STEREO SEPARATION Better than 30dB at 1 kHz AM TUNER SECTION SENS1TIVITY Better than 12pV at 1000kHz (using ex ternal antenna input) SIGNAL TO NOISE RATIO Better than 55dB HARMONIC DISTORTION Less than l%.at 30% modulation FREQUENCY RESPONSE Down 6d8 at 5kHz SELECTIVITY 10kHz at -6dB IMAGE REJECT

4、ION 60dB or greater at 1000kHz FREQUENCY RESPONSE +0.5dB, 20Hz to 20,OOOHz DISTORTION Less than 0.1% at 2.5 volts 20Hz to 20kHz INPUT SENSITIVITY (phono 1 and phono 2) 2 millivolts for 2.5 volts output at 1 kHz INPUT SENSITIVITY (aux, tape) 0.25 volts for 2.5 volts output HUM AND NOISE (phono 1 and

5、phono 2) 72dB below 10 millivolt input HUM AND NOISE (aux, tape) 85dB below rated output OUTPUT (main) 2.5 volts with rated input. Up to 10 volts can be developed without distor tion. FM and AM will produce up to 10 volts output at 100% modulation. OUTPUT (tape) 0.25 volts with rated input. Phono in

6、put signal of 10 millivolts produces 1.2 volts output. FM and AM will produce 1 volt output at 100% modulation. OUTPUT (center channel) 2 volts with rated input to both channels BASS CONTROL -18dB to +16dB at 20Hz TREBLE CONTROL +20dB to 20,OOOHz LF FILTER Flat or roll off below 50Hz, down 12dB at 2

7、0Hz HF FILTER Flat or roll off above 5000Hz, down 12dB at 20,OOOHz FM/AM TUNER SECTION PREAMPLIFIER SECTION MX 112 SCHEMATIC NOTES Unless otherwise specified: Resistance values are in ohms, 1/4 watt, and 10% tolerance; capacitance values smaller than 1 are in microfarads (pF);_ capacitance values gr

8、eater than 1 are in picofarads (pF); inductors are in microhenries (pH). Printed circuit board components are outlined on the schematics by dotted lines. The circled num bers around the dotted lines correspond to the numbers on the PC Board layouts. The heavy lines on the schematics denote the pri m

9、ary signal path. The terminal numbering of rotary switches is for reference only. All voltages indicated on the schematics are mea sured under the following conditions: a. Use of an 11 megohm input impedance VTVM. b. All voltages +10% with respect to chassis g round. c. No signal at input or antenna

10、 terminals. d. AC input at 117 volts, 50/60Hz. e. Front panel controls at: Tuning indicator 100MHz (no signal) Volume Ful 1 y CCW Mode Stereo Muting Input Selector Panel Lights Out AM (to measure AM section) FM (to measure FM section) Bright . In units with serial numbers below 11S00: C25 is connect

11、ed to pin 4 of T3; pin 3 of T3 is connected to ground; C31 is connected to pin 4 of T5; pin 3 of T5 is connected to ground. 2. In units with serial numbers below 11S17 : C25 and C31 are 2.2pF; C33 is 6.8pF and is con nected to pin 5 of T3; C35 is .OOlpF; C60 is not used; R20 is 33k; R23 is 33k and i

12、s con nected as shown by clotted line; L9 (part num ber 122-013) is used in place of R62; D7 and C61 are not used; R225 is 470k; R206 and C203 (part number 064-069) are used and are con nected as shown by dotted line. R2 is con nected to the other end of Rl as shown by dotted line. 3. R221 is used i

13、n units with serial numbers be- 1ow 14S01. 4. In units with serial numbers from 17S40 to 22S65: R63 is used in place of L10; R64 and C128 are used. 5. In units with serial numbers from 17S25 to 17S75. C73 is used. 6. In units with serial numbers below 17S25: R35, R38, R41 , R43, and R44 are used; LI

14、 5 is used; R37 is 470k; R55 Is lk; R52 is 1M and R15 is 6.8M. 7. In units with serial numbers below 17S40: C345 is used; R397 and R398 are not used. 8. In units with serial numbers below 1 8S35, C1 29 is not used. 9. In units with serial numbers below 20S00: R53 and R59 are lOOP; R65 is not used; L

15、l, R6, R61, and CIO are used; there is no connection from C12 to pin number 1 on the mixer and local oscillator PC Board; and C7 is connected to L3 as shown by dotted line. 10. In units with serial numbers from 19S63 to 31S34, R66 is used. 11. In units with serial numbers from 20S72 to 31S35, R67 an

16、d R68 are used. 12. In units with serial numbers below 26S01 : R55 is 270Q; R69 and SI are not used. 13. In units with serial numbers below 25S1I, R399 and R400 are not used. (continued on alignment page) MX 112 LEFT CHANNEL PREAMP. PRINTED C RIGHT CHANNEL PREAMP. PRINTED CIF MX 112 MPX PRINTED CIRC

17、UIT BOARD 043-974 POINTER DRIVE TUNING CONDENSER DRUM POINTER ADJUSTMENT SCREW jr Before stringing unit, turn pointer adjustment screw until pulley A is in the center of its travel. String unit as shown. After stringing unit, turn tuning shaft until pointer is as far to the left as it will go. Turn

18、the pointer adjust ment screw until the pointer coincides with the zero bar of the logging scale. Turn the tuning knob making the pointer move back and forth from one end of the dial scale to the other. Return pointer to the far left and, if necessary, re adjust pointer position. TUNING CONDENSER DR

19、UM TUNING CONDENSER DRIVE BLACK DIAL CORD DIAL CORD SEQUENCE ( TO LEFT SIDE PULLEY 8) WHITE != (TO IDLER PULLEY AND TUNING SHAFT) SLACK * WHITE (TO RIGHT SIDE PULLEY A ) - BLACK (TO TUNING SHAFT) TUNING CONDENSER DRUM POINTER DIAL STRINGING ED CIRCUIT BOARD 043-954 COAX IOZO PRINTED CIRCUIT BOARD 04

20、3-983 POWER SUPPLY / CENTER CHANNEL SECTION SCHEMATIC NOTES (CONT.) In units with serial numbers below 31S34, R130 is not used. In units with serial numbers below 31S35: C25 is 1.2pF; C31 is .5pF; C33 is .OOlpF; C73, C74, C75, C76, R70, R71, R72, and R226 are not used. In units with serial numbers b

21、elow 31S35, the drain of Q4 is connected directly to pin 17 on the AM PC Board and gate 1 of Q4 is connected directiy to C1 9 In units with serial numbers from 26S01 to 31S35, R55 is 56k. In units with serial numbers below 31S35, C20 is .01pF. In units with serial numbers below 31S56: R31 is 100k; R

22、336 is 18k; C126 is used; Cl 30 and Cl 31 are not used; C17, C24, C26, C27, C28, C29. C30, C32, C36, C37, C38, C39, C45, C46, C47, C48, C49, and C51 are .047pF. In units with serial numbers below 31S56: R23 is 15k; R27 is 1.5k; R62 is 2.7k, and Rl5 is 1M. In units with serial numbers below 31S68, R5

23、7 is used; R52 is 100k and the AM sensitivity switch is wired as shown by dotted lines. In units with serial numbers from 31S35 to 31S86, C56 is 1.5pF. In units with serial numbers below 37S50, Rl31 is not used and R105 is a 200k potentiometer (McIntosh part number 134-205)* MX 112 MX 112 I MX 112 -

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35、ER MODIFICATION MODEL: MX 112 Tuner Preamplifier PURPOSE OF MODIFICATION: To increase effectiveness of SCA fi1 ter . WHAT UNITS ARE AFFECTED: Serial No. 10S01 to 31S55 only. WHEN MODIFICATION SHOULD BE MADE: When a customer complains of birdies, whistles, or other noises on certain multiplex station

36、s. MclNTOSH MODIFICATION KIT NO. : No kit available. PART REQUIRED: Quantity Description 1 150pF 20% Ceramic Disc Capacitor RMC type JG or equal. PROCEDURE: Step 1 Remove bottom cover of the MX 112. Step 2 Remove the perforated cover from the MPX section. Step 3 Solder the capacitor in parallel with

37、 R129, a 47k resistor that connects between the SCA filter and the base of Q102. Keep leads short. Step A Feed a 1 volt 67 kHz signal from an audio oscillator into TP #2 of the MX 112. Observe the signal on a scope at the tape output. Adjust the SCA filter for minimum 67 kHz in the output. Step 5 Replace the covers. 038-375 McIntosh Laboratory Incorporated 2 Chambers Street Binghamton, New York 13903 Phone: Area Code 607-723-3512