McIntosh Service Bulletins.pdf

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1、MODEL NUMBER MA 230 DATE June, 1964 MODIFICATION MA 230 serial 4 10C00 to # 13C03 to increase overall gain. DESCRIPTION This modifica.tion may be incorporated in MA 230 units having the above serial numbers to increase the overa.ll gain. The gain is increased two ways: 1. The feedback loop in the ph

2、ono-tape head input stages is modified by changing the input transistor emitter resistors (R 17 and R 18) from 1.8K 5% % watt to 1.2K 5% % watt. 2. The volume control taper characteristic is changed to a.llow more amplification at a lower setting of the control knob by changing the resistors connect

3、ed to the rear of the loudness control (R 39 and R 40) for 47K 10% watt to 100 K 10% % watt. These modifications have been made in all MA 230 with serial numbers above 13C03 . MA 230 MODEL NUMBER MA 230 DATE June, 1964 MODIFICATION MA 230 serial # 10C00 to # 17C50 to decrease hum introduced when H.F

4、. filter switch is depressed. DESCRIPTION This modification may be incorporated in MA 230 units with the above serial number to decrease hum introduced when the H.F. filter switch is depressed The hum introduced comes from a. 120 cycle ripple component on the fila.ment supply coupling to the input g

5、rids of the 12AX7 tube. This coupling is eliminated by adding two resistors to balance the filament supply with respect to ground. The pilot lamp is rewired as a pa.rt of the modification. These modiciation have been made in all MA 230s with serial numbers a.bove 17C50 . PROCEDURE i. Remove bare wir

6、e from pilot light socket to ground. 2. Remove bare wire from pin 7 of to ground. 3. Install new wire to pilot light and two 100 ohm 10% watt resistors as shown below: POWER TRANS WIRE FROM PIN*7 TO 8ROUND LUS REMO VEC BOTH 130A RESISTORS ARE CONNJE.CTED TO WEARE3T TUBE SRNO MA 2 30 MODEL NUMBER MA

7、230 DATE September, 1964 MODIFICATION INSTALLATION OF A 4 SECTION VOLUME CONTROL PROCEDURE 1. Remove the black ground wire running from the volume control to the balance control. 2. Install terminal strip on the printed circuit board. Use the existing bolt and nut. 3. Cut the audio cables attached t

8、o the card. Cut them long enough to be connected to the terminal strip as shown in the diagram. 4. Remove the existing volume control. Pay strict attention to how the wires are connected. (The two front sections of the new volume control are identical to the existing control; the two rear sections a

9、re those added.) 5. Install the new volume control and wire according to the diagram. Connect the 5 jumper wires. Make sure they are insulated from tie control frame. Use insulated wire or spaghetti. Do not alter the lead arrangement or the grounding method. Hum may be introduced if you do so. MA 23

10、0 * s H/EIP/YG !Y/S /r*OM 7*/S * 77 rOSTA/f MA-230 INSTALLATION OF 4-SECTION VOLUME CONTROL MODEL NUMBER: Ml 2 DATE: MARCH 1965 MODIFICATION: To eliminate any shape other than a dot when in the TEST position. DESCRIPTION: This modification can be made to all Ml 2s. If a configuration other than a sh

11、arply defined spot occurs this indicates possible oscillation in the deflection amplifier. Noise in the deflection amplifier can also cause this condition. Oscillation is caused by coupling between pins 1 and 2 of tubes VI and V3. Noise can be caused by parasitic oscillations of intensity control ne

12、on bulbs and by coupling of power line noise into the + 108 volt supply via the filament winding on the power trans former. These modifications have been made to all Ml 3s. PROCEDURE: 1. There are two 10 w resistors under the chassis/ parallel each of these with a 56K 2 w resistor. 2. Remove the neo

13、n bulb from the intensity control. 3. Add a 270K 14 w resistor from the center lug of the intensity control to the side lug (at junction of yellow/white wire and 390 K resistor). Add a jumper wire from the center lug of the control to the other lug (junction of orange/white wires). 4. Remove the red

14、/white wire from pin 5 of the 6U8 (6) to pin 1 of the OB 2 (V8). Replace the wire with a 47K 14 w resistor. 5. Add a lOpf capacitor from pin 2 to pin 6 of tubes VI and V3. Bend the tube socket of pins of tubes VI and V3 so that pin 1 is as far away from pin 2 as pos sible. Dress the leads connecting

15、 to these pins for maximum separation. MODEL NUMBER: Ml 2 DATE: MARCH 1965 MODIFICATION: To eliminate any shape other than a dot when in the TEST position. DESCRIPTION: This modification can be made to all Ml 2s. If a configuration other than a sharply defined spot occurs this indicates possible osc

16、illation in the deflection amplifier. Noise in the deflection amplifier can also cause this condition. Oscillation is caused by coupling between pins 1 and 2 of tubes VI and V3. Noise can be caused by parasitic oscillations of intensity control neon bulbs and by coupling of power line noise into the

17、 + 108 volt supply via the filament winding on the power trans former. These modifications have been made to all Ml 3s. PROCEDURE: 1. There are two 10 w resistors under the chassis, parallel each of these with a 56K 2 w resistor. 2. Remove the neon bulb from the intensity control. 3. Add a 270K I/2

18、w resistor from the center lug of the intensity control to the side lug (at junction of yellow/white wire and 390 K resistor). Add a jumper wire from the center lug of the control to the other lug (junction of orange/white wires). 4. Remove the red/white wire from pin 5 of the 6U8 (6) to pin 1 of th

19、e OB 2 (V8). Replace the wire with a 47K Vi w resistor. 5. Add a lOpf capacitor from pin 2 to pin 6 of tubes VI and V3. Bend the tube socket of pins of tubes VI and V3 so that pin 1 is as far away from pin 2 as pos sible. Dress the leads connecting to these pins for maximum separation. POWER SUPPLY

20、C.R T. CIRCUIT MODEL NUMBER: C 8, C 11, C 22 DATE: APRIL 1965 MODIFICATION: Replace the selenium rectifier with silicon rectifiers. These silicon rectifiers have much longer life. DESCRIPTION: The original selenium rectifier in the C 8 is replaced by two (2) silicon rectifiers; the original selenium

21、 rectifier in the C 11 and C 22 is replaced by four (4) silicon rectifiers. The rectifiers are McIntosh part number 070-014, or any 50 PIV 750 MA rectifiers. PROCEDURE: The selenium rectifier is replaced by a terminal strip and the new silicon rectifiers are installed as shown in the following diagr

22、ams. NOTE THAT TERMINAL STRIPS ARE REQUIRED C 8, C 11, C 22 MODEL NUMBER: MA 230 DATE: MARCH 1965 MODIFICATION: Tightening the transformer mounting screws to eliminate buzzing. DESCRIPTION: The top and bottom transformer laminations will vibrate when they are not secured by the impregnating varnish

23、or clamped by the transformer end-bells. Some MA 230s transformers have the problem. PROCEDURE: Tightening the transformer mounting screws may secure the laminations enough to eliminate the buzz. If this fails thin shims should be inserted between the lami nations and the end bells. TO INSERT THE SH

24、IMS: 1. Loosen the transformer mounting screws. 2. Insert two shims under each end-bell. Make the shims from metal or fiber. The shims should be 3 x W x 1 /16. 3. Re-tighten the mounting. MA 230 MODEL NUMBER: MR 65B, MX 110, MR 67 DATE: MARCH 1965 MODIFICATION: To allow adjust control for instant co

25、rrection of tube and circuit variations. This will insure proper MPX indicator light operation. PROCEDURE: This modification will allow you to adjust the MPX light on all tuners with ease. The reason for this modification is to allow simple field adjustment of varying tube and circuit characteristic

26、. MR 65B and MX 110 tuner/preamp. 1. Install IK control (WC 807) to MPX chassis. Use the existing MPX chassis mount ing screw. 2. Remove the 820 ohm or IK ohm resistor, (cathode circuit of 6U8) 3. Solder one end of 470 ohm resistor to bottom hole nearest the chassis. 4. Connect a lead from other end

27、 of the resistor to the terminal lug on a 1K control. 1. Install IK control to the tuner chassis under the existing screw as shown in the diagram. 2. Follow steps 2, 3, 4, as above. TO ADJUST THE CONTROL: Tune to point of no station. Place mute to IN position. Turn control from full clockwise positi

28、on to a point where the light just goes out. MR 65B, MX 110, MR 67 DATE: NOVEMBER, 1965 MODEL NUMBER: C 22 MODIFICATION: Replacement information for circuit modules. PROCEDURE: C 22s built before 1965 used circuit modules made by Erie Electronics. In 1965 we changed to Sprague Electric Co. The Sprag

29、ue modules are electrically equivalent to the Erie modules but differ mechanically. The newer Sprague modules are used for replacement when servicing early C 22 units. The attached schematic shows the lead connections for both the Erie modules (PC 120-161, PC 120-133, PC 120-132, PC 120-134, PC 120-

30、138, and PC 120-160) and the Sprague modules (130-015, 130-016, 130-017, 130- 018, 130-019, 130-020, and 130-021.) Follow the schematic to replace an Erie module with a Sprague module. NOTE: The Sprague 130-015 replaces 2 each PC 120-161 units, and a Sprague 130-018 plus a 130-019 replaces one PC 12

31、0-134. DATE: NOVEMBER, 1965 MODEL NUMBER: MX110 MODIFICATION: Popping noise from the speakers when the switch controls on the MX110 are operated can be caused by leaky .1 MFD disc ceramic coupling capacitors. Changing these capacitors to high insulation resistance mylar units will eliminate the prob

32、lem. MX110 equipment built since April 1965 have this change. PROCEDURE: Replacement of capacitors. A. If a popping is heard when depressing the LF filter replace C 97 or C 98. They are located on the LF filter switch. The replacement part number is 064-027. (.1 mfd 40 v). B. If a popping is heard w

33、hen rotating the mode selector switch replace C 93 and C 95, or C 94 and C 96. The components are to be replaced with one 064-024. (.22mfd 40v). C 97 and C 98 may also cause popping. C. If a popping is heard when rotating the input selector switch between MPX and AUX or FM MONO, replace C 72, C 76,

34、or C 52. Use 061-0455. (.02 mfd) D. If a popping is heard when rotating the input selector switch to various positions, replace C 91 or C 92. Use 061-045. (.02 mfd). E. If a high level of distortion is present on FM mono, replace C 54. Use 064-028. (.1 mfd 200 v). NOTE: All of the above replacement

35、parts should be acquired from McIntosh Lab. OUXVV m PRODUCT: MI-2/MI-3 MODIFICATION: CIRCUIT CHANGE TO PREVENT POWER TRANSFORMER FAILURE. DESCRIPTION: Power transformers have failed in some M1-2/M1-3 units due to intermittent shorts in the 6W4 HV rectifier tube. These shorts are caused by cathode fl

36、aking in the 6W4. The problem can be eliminated by replacing the 6W4 with a 3000 volt 3MA semiconductor rectifier. This modification reduces the amount of heat generated within the MI-2/MI-3 and increases the life and reliability of the unit. PROCEDURE: 1. Remove the MI-2/MI-3 top cover. Remove the

37、6W4 tube and place an octal plug (Part #127-006) in the socket. 2. Remove the MI-2/MI-3 bottom cover. Cut and remove the jumper wire connecting pin 8 to pin 3 on the 6W4 socket. Connect the 3000 PIV rectifier (Part #070-026) to pin 5 and pin 3 of the 6W4 socket. The RED end of the rectifier should c

38、onnect to pin 3 and the BLACK end to pin 5. This part of the circuit operates at 1300V; therefore, be sure to locate the rectifier and its leads to provide ade quate insulation. Use spaghetti on the rectifier leads. Keep the rectifier leads short to avoid rectifier vibration problems. 3. This comple

39、tes the modifications. Service bulletin 104 also relates to this product. If trouble has been experienced this modification should be installed at this time. MI-2/MI-3 NOVEMBER, 1965 MODEL NUMBER: MAC 1500, Serial Numbers below 11F99 MODIFICATION: To increase audio gain in all input positions. This

40、modification changes the volume control taper to give about 8db more gain. It does not increase the gain in the full volume position. PROCEDURE: Refer to the schematic on this bulletin. Find resistors R 130 and R 131 and capacitors C 100 and C 101. These components connect to the volume con trol. Re

41、move them from the receiver. Replace R 130 and R 131 wilh 5.6K 5% A watt resistors. Replace C 100 and C 101 with .047 mfd 10% mylar. MATERIAL NEEDED: 2 each resistors, 5.6K 5% !4 watt. 2 each capacitors, .047 mfd 10% mylar. These parts are available in modification kit #9043-543. MAC 1500 MODEL NUMB

42、ER: MX110 Z and X series. DATE: JUNE 1966 MODIFICATION: This modification eliminates both the opening of the tuning eye after warm up, and the muting threshold change with tuner warm up. The drift problem is corrected by replacing the IF transformer T 4. T 4 is replaced by a transformer of improved

43、design. There are several circuit modifications that must also be made. Part of the change includes adding a potentiometer. This potentiometer allows ad justment of the amount of tuning eye closure. After the modification has been made it is necessary to align the IF transformer T 4, the tuning indi

44、cator adjustment, and the muting adjustment control. PROCEDURE: 1. Remove IF transformer T 4. Replace this transformer with McIntosh part #162-029. Remove and do not connect back into the circuit capacitor C 24 and the small parallel lead capacitor that was between pins 1 and 4 on the transformer. 2

45、. Replace diode D2 with a new diode, McIntosh part #070-022. 3. Change R 33 from 100K to 47K 10% 1/2W. This is McIntosh part #136-180. 4. Remove the present muting control. Discard it. Install a dual control. (#134-168). The top of the dual control is re-wired as the previous muting control. The bot

46、tom of the control is the new control. 5. Connect the end contact of the tuning indicator adjust control to the end contact of Rl. 6. Remove resistor R 35. Replace it with a short section of wire. Solder the wire to ground. 7. Disconnect the end of R 32 which connects to feed through capacitor C33.

47、Con nect this end of R 32 to the arm contact on the tuning indicator adjust control. To make this connection extend the lead on R 32. Use a short section of wire and spaghetti tubing. 8. Align and adjust the MX 110 as follows: If proper alignment equipment is at hand use procedure A. If limited test

48、 equipment is available use procedure B. A) Switch the MX 110 muting control to the out position. Connect a 10.7MC signal to the grid of the first IF amplifier. Feed in enough signal to develop at least 10 volts at test point 1 (TP-1). Turn the tuning indicator adjust control to mid position. Adjust

49、 T-4 top and bottom cores for maximum tuning indicator closure. Then adjust the tuning indicator adjust control for 1/16 opening of the tuning eye. With the 10.7MC signal connected to the MX 110 check the adjustment of IF transformer T 5. Measure the DC voltage present at test point 2 (TP-2). If this voltage measures more than 0.2 volts, adjust the top core on T 5 so the voltage at TP-2 is zero. DO N