McIntosh MAC1500 - SERVICE 1 User Manual download pdf (Page 4)

FM ALIGNMENT

ADJUST

Top (secondary)

and bottom

(primary) of

T1.T2, T3

Primary and

secondary of

Secondary

(top)

T-5

-4

L-4

C-2,

C-3

L-1, L-2,

Primary (bottom)

of T-5

L-2,

C-3

Muting threshold

control

TEST

LIMITS

Maximum pos-

sible negative

voltage

Maximum pos-

sible negative

voltage (should

be 20 to 30

volts)

Adjust for 0 volts

Maximum nega-

tive voltage

SAME

0.5% distortion

or less

Minimum tilt

IHFM Sensitivity

2.5 microvolts

for 3% total

noise and

distortion

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 trans-

former 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.

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.

direction

is the

same,

adjust

L-2 at

100MC

for

minimum

tilt.

Re-check

tilt

90MC

and

105MC.

direction

is not the

same, adjust

L-2 (at

90MC)

and L-3 (at

105MC)

for

minimum

tilt.

Check

tilt

again

100MC.

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.

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McIntosh MAC1500 - SERVICE 1 User Manual Page 4

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