Marantz 1120 Schematic Adjustments

Page 1

0

-Ca JESS C SUIT TEST

1. Connect Audio Oscillator to both chan-
nel AUX input jacks. Adjust level for
21.9V output into the 8 ohm load. Ad-
just unit VOLUME control (from MAXl-
MUM) for a 30dB reduction in output
level.

2. With oscillator frequency at 100Hz, com-
pare output level with LOUDNESS switch

1N and OUT. Verify a 7dB :2dB boost
with switch IN.

3. Change oscillator frequency to 10KHz.
Verify a 7dB :ZdB boost in output volt-
age when LOUDN ESS switch is depressed.

ADJUSTMENT
PROCEDURE

A.

TEST EQUIPMENT

Refer to Table 1 for recommended test
equipment.

PRELIMlNARY PROCEDURES

The preliminary procedures outlined in the
Performance Verification section of this man-
ual are applicable in their entirety.

UNIT DISASSEMBLY

Remove the top cover. (See Service Notes
section for disassembly instructions).

BIAS ADJUST

1. Turn Line Switch to OFF. Rotate the
bias adjust potentiometers R523 and
R524 fully C.W. (See Figure 14 for
component locations).

2. Switch the Wattrneter IN and set the

Variac to 0.

3. Turn the Line Switch ON and slowly ad-

vance the Variac to 120 VAC while ob-
serving the Wattmeter. The Wattmeter
should indicate less than 35W at 120V.
lf the Wattmeter indicates either 0 or
greater than 35W, a defect exists. Turn
off the unit and correct the fault.

4. Reduce the unit VOLUME to minimum.

Connect a lowrange voltmeter across
series combination of R553 and R549
(voltmeter in 0-100mV range). See Fig-

ure 14 for component and connection
point location.

5. Adjust R523 :or voltmeter reading be-

tween 11 and leV.

5. Change location of voltmeter to series

combination of R550 and R554. See
Figure 14.

7. Adjus1 R524 for voltmeter reading be-

tween 11 and 18mV.

Note: 11mV drop across the series resis-
tance represents SOmA idling current in
the output stage. 18mV represents SOmA
idling current.

DC BALANCE ADJUST

1. Monitor the left channel output with a
VTVlVl in the DC mode.

2. With the unit VOLUME control set to
minimum, adjust the left channel Zero
Set potentiometer R517 for a DC output
voltage of 0V :SOmV. (See Figure 14
for component location).

3. While monitoring the right channel out-
put, adjust the right channel Zero Set po-
tentiometer R518 for a DC output volt-
age of 0V iSOmV.