Marantz PROFESSIONAL Series - Test Equipment; Preliminary Procedures; DC Balance Adjustment; Bias Test

All tests outlined below should be performed
after any adjustment or repair. Refer to the
Trouble Analysis section of this manual should
any test results be other than what is specified in
the test procedures. Unless otherwise specified,
all tests are to be performed on both audio
channels, with the results indicated applying
equally to both channels.
A.
TEST EQUIPMENT
Refer to Table 1. for list of recommended
test equipment.
PRELIMINARY PROCEDURES
1. All tests are performed with the unit
under test and the test equipment con-
nected as shown in Figure 4. All tests
are conducted with 120 VAC line voltage
applied to unit. Unless otherwise specified
in the procedure, the test equipment
controls will be set to the following
positions.
AC Power Contro} Box:
Line Switch... .......00 eee eeee ON
Wattmeter Switch.......... DIRECT
Variable
Autotransformer..... 120 V AC LINE
Amplifier Output Load Box:
Channel Select... SET FOR CHANNEL
UNDER TEST
Load Switch.......... AS REQUIRED
BY TEST
Capacitance Switch............. OFF
During all test procedures the controls of
the unit under test will be set as follows
unless otherwise specified.
Gain Controls............ MAXIMUM
Meter Range... .... 0. eee ee eee OFF
. Connections, between the output (load-
speaker) terminals of the Model 510
Series and the Output Load Box, must
have negligible resistance with respect to
the resistance of the load itself. Apprecia-
ble resistance adds to the total load,
resulting in inaccurate measurement of
output power. All test equipment should
be connected to the amplifier.
. Refer to Figure 15, Schematic Diagram
and Figure 16, Wiring Diagram to locate
detailed parts and wires referenced.
DC BALANCE ADJUSTMENT
I
Connect oscilloscope and set vertical am-
plifier in DC position and connect to
L channel loudspeaker terminal.
CAUTION: Resistor R3 must be shorted
with a Jumper whenever an Autotrans-
former is used.
. Set Line Switch and Wattmeter to ON and
slowly advance autotransformer to 120
VAC observing that the wattmeter indica-
tion does not exceed 130 W.
. Adjust L Channel (Left Heatsink Module)
amplifier board, Output Offset potentio-
meter R310, for an indication of a ‘‘line’”’
zero (OV + 50 mV) as indicated on the
oscilloscope.
. Repeat test for R Channel (Right Heatsink
Module).
BIAS TEST
ts Set Line Switch to OFF. Preset the Bias
Adjustment potentiometer R331 on each
amplifier board fully CCW.
Disconnect load, set the Wattmeter to
ON and set autotransformer to 0.
. Set Line Switch to ON and slowly advance
autotransformer while observing the Watt-
meter. The Wattmeter should indicate less
than 130 W at 120V. If the Wattmeter
indicates either 0 or more than 130 W,
unit is defective. Turn off and correct
fault.
BIAS ADJUSTMENT
1.
Make certain load is disconnected. Con-
nect a digital voltmeter across series com-
bination of R359 and R360 or R361 and
R362.
. Adjust the L Channel Bias Adjustment
potentiometer R331 for voltmeter reading
between 18 mV and 34 mV.
. Repeat for R Channel.
Note: A 18 mV drop across the series
resistance (R359 and R360 or R361
and R362) represents 30 mA idling
current in the output stage. A 34 mV
drop represents 57 mA idling current.
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