McIntosh MAC-1500 Service manual

MAC 1500 STEREO RECEIVER

WARRANTY STATION

SERVICE MANUAL

CONTENTS

INTRODUCTION 1
FM ALIGNMENT CHART 2-3
MULTIPLEX DECODER ALIGNMENT CHART _ 4-5
SCHEMATIC 6-7
TESTS AND ADJUSTMENTS 8

DIAL STRINGING 8

PARTS LIST 9-14
TOP AND BOTTOM VIEWS 15

SPECIFICATIONS 16

BLOCK DIAGRAM 16

MAC 1500

McINTOSH AUDIO COMPANY

2

Chambers St., Binghamton, N.Y.

13903

MAC 1500 STEREO RECEIVER

INTRODUCTION

All Mclntosh tuners are carefully aligned and tested at the factory using the finest
available test equipment. All Mclntosh tuners will meet their published specifica­tions when shipped from the factory.

After extensive operation, especially when tubes have been replaced, it may be
desirable to realign the timer circuits for best performance. This manual gives
complete information on the circuit realignment procedure for the MAC 1500
receiver.

The test equipment listed below (or its equivalent) is necessary to properly
align a MAC 1500. The accuracy of the alignment will be directly related to the
accuracy and calibration of the test equipment used.

FM Signal Generator (Measurements 210A or equivalent)

VTVM

Multiplex Generator (RCA WR51A or equivalent)

10.7 MC Generator (Preferably crystal controlled)

Oscilloscope (Hewlett -Packard 120B or equivalent)

Harmonic Distortion Analyzer (Hewlett-Packard 330B or equivalent)

If the necessary test equipment is not available, alignment should not be
attempted. You may contact the Mclntosh Customer Service Department for
additional information.

Customer Service

Mclntosh Laboratory, Inc.

2 Chambers Street

Binghamton, New York

Our telephone number is 723-5491

The direct dial area code is 607

1

MAC

1500

STEPS

1

2

3

TUNER

DIAL

SETTING

Point of no
interference
and no signal

SAME

SAME

FREQ.

10.7MC

SAME

SAME

SIGNAL GENERATOR

COUPLING

Through external
.01 MFD capacitor
to mixer grid (pin
4 or 6DS4, V2)

SAME

SAME

MODULATION

cw

SAME

SAME

TYPE

VTVM

SAME

SAME

INDICATOR

CONNECTED

TO

TP#1

Pin 1 of T4

TP#2

4
5

6

7

8

9

10

11

105MC

90MC

105MC

90MC

90MC

105MC

90MC

90MC

90MC

and

105MC

90MC

105MC

90MC

90MC

105MC

and

90MC

90MC

90MC

300 ohm antenna
terminals with
matching network*

SAME

SAME

SAME

SAME

SAME

SAME

SAME

400 cycles

75KC deviation

(100% modulation)
SAME

SAME

SAME

SAME

50 cps 150KC
deviation Approx.
5 microvolts at

antenna terminals
400 cycles

75KC deviation
(100% modulation)

SAME

VTVM connected to TP#2 and.

scope connected

output
SAME

SAME

SAME

VTVM connected to TP#2
scope and distortion analyzer
connected to L or R tape
output

See note ** at bottom of page

Scope connected to L or R
tape output

VTVM connected to TP#1
scope and distortion analyzer
connected to L or R tape

output

to L or R

tape

;

;

2

FM ALIGNMENT

ADJUST

Top (secondary)
and bottom
(primary) of
T1.T2, T3

Primary and

secondary of

T4

Secondary
(top)

of

T-5

TEST

LIMITS

Maximum pos­sible negative
voltage

Maximum pos­sible negative
voltage (should

be 20 to 30

volts)

Adjust for 0 volts

REMARKS

Before making any adjustments, set the controls as follows:

a) Input selector switch to FM mono,
b) Volume control maximum CCW.
c) Muting pot maximum CW.
d) Muting OUT.
e) Stereo light adjust maximum CW.

Shunt to ground the winding not being adjusted. Do this with a .01
MFD capacitor in series with a 1K resistor. Attenuate signal generator
until output voltage at TP#1 is less than 1.5 volts with one IF trans­former winding shunted. IF transformers have terminal #1 marked
with a green dot and are numbered clockwise.

Muting pot. MUST be maximum CW.

The primary (bottom) of T-5 should be adjusted only if a distortion
analyzer is available.

_

-4

L-4

C-2,

C-3

L-1, L-2,

Primary (bottom)

of T-5

L-2,

Muting threshold

control

L3

C-3

Maximum nega­tive voltage

SAME

SAME

SAME

0.5% distortion
or less

Minimum tilt

IHFM Sensitivity

2.5 microvolts
for 3% total

noise and

distortion

Repeat steps 4 and 5 until dial calibration is accurate.

As output increases, attenuate signal generator to keep maximum out-

put at TP#1 to less than 1 volt.
Repeat steps 6 and 7 until output is as high as possible.

Use a strong signal from the FM generator. Adjust T-5 primary for
minimum distortion. IF A DISTORTION ANALYZER IS NOT AVAILABLE,
OMIT THIS STEP. DO NOT ADJUST T-5 PRIMARY.

Observe direction of tilt of overall response curve at 105MC and 90MC.
If

direction

tilt

at

90MC)

With FM generator set for 2.5 microvolts output, place muting control

to "IN." Adjust the muting threshold control to the point at which the
sine wave on the scope becomes erratic.

Step 11 is an overall sensitivity check. It requires a distortion analyzer
and FM signal generator with attenuator. With 2.5 microvolts input at
the 300 ohm terminals, TP#1 voltage should be .45 volts or more.

is the

90MC

and

and L-3 (at

same,

105MC.

105MC)

adjust

If

for

L-2 at

direction

minimum

100MC

for

minimum

is not the

tilt.

Check

tilt.

Re-check

same, adjust

tilt

again

at

L-2 (at

100MC.

3

MAC 15 00 MULTIPLEX

STEPS

1

2

3

TUNER

DIAL

SETTING

Point of no
interference
or signal

SAME

100MC

FREQ.

Audio gener­ator set to 67KC

0.5 volts out­put or less

MPX generator
with 19KC pilot
attenuated to
approx. 5%

level. (5% level
is ½ of normal

10% level).

19KC pilot
MUST be at­tenuated for
correct align-

ment

100MC modu-

lated by MPX

generator.

19KC pilot at

normal output

SIGNAL GENERATOR

COUPLING

TP#2

SAME

300 ohm

antenna termi-

nals with
matching net­work. (See *
previous page)

1KC 100% modu­lation
deviation) modu­lating left or
right only

MODULATION

(34 KC

TYPE

Audio
VTVM

DC

VTVM

Audio
VTVM

INDICATOR

CONNECTED

TO

L or R tape output

Pin 9 of 6EA8

Pin 1 or 2 of T-7

4

5
6

7

8

SAME

SAME

SAME

SAME

SAME

SAME

SAME

SAME

SAME

Tune to a strong

mono FM
station

SAME

SAME

SAME

SAME

SAME

SAME

SAME

SAME

Turn off 1 KC audio
modulation

Audio
VTVM

and

scope

SAME

SAME

SAME

MPX

stereo
indi­cator
light on
receiver

L or R tape output

SAME

SAME

SAME

4

DECODER ALIGNMENT

ADJUST

67KC Trap (L-6)

T-6 top and

bottom;

L-5

T-7 bottom core

TEST

LIMITS

Adjust for mini-

mum voltage

Adjust for maxi­mum voltage

SAME

REMARKS

Stereo light must be on. This is done by adjusting the "MPX Light
control, R-12.

Stereo light must be off.

• ~

Stereo light must be completely on.

Adj."

T-7 top core

L-5

MPX light adjust
control R-12

Adjust for stable
scope display

1. Turn off 19KC pilot on MPX generator.

2. Adjust upper core of T-7 to obtain a stable and uniform 1 KC signal
scope display. This adjustment may be critical, so turn core very
slowly.

3. Turn 19KC pilot back on.

30db separation
or more

Modulate left channel and measure right channel output. Adjust L-5 for

minimum right channel output (maximum separation). Be sure all test
leads are removed from TP#2 for separation tests.

SAME

Modulate right channel and measure left channel output. Separation in
steps 5 and 6 should be at least 30db.

This step checks the rejection of 19KC and 38KC frequencies. Residual output should be
at least 40db below modulated output.

Turn control until light comes on. Then back off just enough to cause

the light to go off. Then back off about 1/8 of a turn more. Light should
operate ONLY on a MPX signal.

5