McIntosh MAC1700 Receiver Schematic Diagram.pdf

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1、MODEL MAC 1700 STEREO FM RECEIVER McIntosh audio company 2 CHAMBERS STREET BINGHAMTON, N. Y. 13903 038-136 Unless otherwise specified, resistance values are in ohms, 1/2 watt, and 10% tolerance. Capacitance values smaller than 1 are in microfarads (MF); values greater than 1 are in picofarads (PF).

2、Inductors are in micro henries . Rotary switches are viewed from the front with the knob in the extreme counterclockwise position. The terminal numbering of rotary switches is for reference only. All voltages are measured under the following conditions: 1. Use of an 11 megohm input impedance VTVM vo

3、ltmeter. 2. All voltages +10% with respect to ground. 3. No signal at antenna or other input terminals. 4. AC input at 117 volts, 50/60 cycles. 5. Front panel controls at: Mode Selector Stereo Input Selector Aux Volume Control Max Balance Control Zero Tone Controls Flat Muting Out Filter Out Loudnes

4、s Out Tape Monitor Out MODEL MAC 1700 RECEIVER 8.2K I/4W 5% 8.2K I/4W 5% R6A T 75K II vl CIIO If- I.5MF v? OUTPUT (TO INPUT OF POWER OUTPUT SECTION) o _I MclNTOSH LABORATORY INC. SCHEMATIC DIAGRAM PREAMPLIFIER SECTION MODEL MAC 1700 RECEIVER SCHEMATIC NO. I54“23l REVISION R 35 1/4 W mcintosh laborat

5、ory inc. SCHEMATIC DIAGRAM IF/MPX SECTION MODEL MAC 1700 RECEIVER SCHEMATIC NO. 154-234 SPEAKER OUTPUT left channel power output printed circuit board HEADPHONES RIGHT CHANNEL POWER OUTPUT PRINTED CIRCUIT BOARD RIGHT SPEAKER OUTPUT MclNTOSH LABORATORY INC. SCHEMATIC DIAGRAM POWER OUTPUT SECTION MODE

6、L MAC 1700RECEIVER SCHEMATIC NO. 154-232 REVISION MAC-1700 RECEIVER (POWER AMPLIFIER SECTION) Page -1- Servicing the MAC-1700 solid state amplifier section is easy. Transistor and tube type amplifiers have much in common. It is necessary to learn only a few basic principles. 1. Being a solid state a

7、mplifier, the circuits are in operation the moment the instrument is turned on. It is important to be certain that all circuits are operating properly before applying full line voltage. If some circuits are not operating properly, it is possible to damage additional circuit components. When a MAC-17

8、00 comes in for service, NEVER JUST PLUG IT IN AND TURN IT ON. Always use a Variac or Powerstat. Plug the receiver into the Variac, but set the Variac output to zero volts. Bring the line voltage to the receiver up very slowly. As you do so, monitor the output voltage on each channel. This is done w

9、ith a VTVM. Connect the common lead of the VTVM to the speaker common terminal or the chassis and the probe to the hot speaker terminal. Set the VTVM on about a 15 volt positive DC scale. Set the needle of the VTVM to the center of the scale rather than to zero. As the line voltage to the amplifier

10、is slowly increased, the VTVM needle will swing positive a few volts, then back past the center position, then slightly negative, then return to center position. This complete cycle will occur before the line voltage to the amplifier reaches 30 volts. Raise the line voltage from zero to 30 volts ver

11、y slowly. Alternate the VTVM probe between the two channels. There may be trouble in only one channel. The channel without the trouble would give a correct indication on the VTVM. So it is necessary to monitor both channels as the amplifier is being turned on. 2. If the receiver is turned on with no

12、 indication of trouble, the next step is to set the bias. By means of the bias pot on the power output printed circuit board, adjust the bias for 40 millivolts. Do this for each channel. This adjustment should be made when the amplifier is cold. Make it within the first minute or so after the amplif

13、ier has been turned on. The bias will vary somewhat as the amplifier warms up. Do not Page -2- readjust the bias. The bias adjustment is made with the VTVM connected as shown: Common Lead Probe POWER OUTPUT PRINTED CIRCUIT BOARD 3. If there ia trouble in one channel, you will not see the indication

14、on the VTVM described in point 1. Stop right there. There are basically three possibilities of incorrect indication. The VTVM needle may not move at all, it may continue to swing positive, or it may continue to awing negative. 4. Regardless of the incorrect indication, it is usually not difficult to

15、 find the source of trouble. Turn the line voltage completely off. Discharge the large filter capacitors. Do not discharge the capacitors by shorting them directly to the chassis. Because of the arcing that will occur, the chassis will be marred. The proper way to discharge these capacitors is with

16、a resistor. Use a resistor of at least a two watt rating whose value ia approximately 5 to 15 ohms. Hold it across each of the large filters. In this way, the power supply will be safely discharged. Failure to discharge the power supply before working on the amplifier could cause several transistors

17、 to be destroyed. Page -3- 5. After the power supply is discharged, check each tran sistor. This is done quite easily with the VTVM. CAUTION: USE VTVM SUCH AS THE RCA SENIOR VOLTOHMYST. Do ret use older 1,000 ohms per volt VOM. This type of instrument may destroy the transistor by introducing excess

18、ive current into the transistor. Set the VTVM to measure ohms; after the power supply is discharged, check each transistor. Set the VTVM to measure ohms; use the R x 1 scale. Measure across each junction of the transistor. Measure from base to collector, base to emitter, emitter to collector, emitte

19、r to base, collector to emitter, and collector to base. Also measure from the case of the transistor to ground. In no case should there be a direct short. In most cases, only one channel of the amplifier will be defective. Therefore, until you become familiar with the readings to expect in each case

20、, compare the defective channel with the good channel. Although a defective transistor will usually be indicated by a direct short, this is not always the case. It is possible for a difference of only 2 or 3 ohms to indicate a defective transistor. For example, if a transistor in the defective chann

21、el reads 12 ohms from one junction to another, and the similar transistor in the good channel reads 10 ohms, the transistor which reads 12 ohms is probably defective. 6. If the transistors all measure correct, check the power resistors at the emitter and collector of the output transistors. These wi

22、ll have a very low resistance of about .33 ohms to .56 ohms. You may find that one of these resistors has opened up. 7. Always check the bias potentiometer for continuity. Be certain that it has not opened up. 8. After replacing a defective part, always turn the amplifier on as described in point 1.

23、 Otherwise, you may damage more parts. For example, you may find a shorted output transistor. You will replace the tran sistor. If there are other defective parts, that you do not yet know about, and you turn the amplifier on directly, in all probability, you will damage the new transistor that you

24、have just installed. Page -4- 9. Before working on the MAC 1700 amplifier section, ALWAYS discharge the power supply as described in point 4. If you do not do so, and then begin probing with a soldering aid, VTVM probe, or what have you, in all probability, you will damage some transistors when you

25、accidentally short from certain places to ground! 10. If the difficulty is not located as described in points 5, 6, and 7 you may turn the amplifier partially on. Bring the line voltage up to 25 or 30 volts. This will be enough voltage to enable you to signal-trace, compare voltages between the good channel and the defective one, etc. without damaging any components.