Maintenance; Cautions And Warnings; General Information; Test Procedures - Crown Macro-Tech MA-2402 Service Manual

130445-1 Rev. A

5 Maintenance

5.1 Cautions and Warnings

DANGER: The outputs of this amplifier can produce
LETHAL energy levels! Be very careful when making
connections. Do not attempt to change output wiring
until the amplifier has been off at least 10 seconds.
WARNING: This unit is capable of producing high sound
pressure levels. Continued exposure to high sound pres-
sure levels can cause permanent hearing impairment
or loss. User caution is advised and ear protection is
recommended when using at high levels.
WARNING: Do not expose this unit to rain or moisture.
WARNING: Only properly trained and qualified techni-
cians should attempt to service this unit. There are no
user serviceable parts inside.
WARNING: When performing service checks with the
power off, discharge the main power supply filter ca-
pacitors fully before taking any measurements or touch-
ing any electrical components. A 300-ohm 10-W resis-
tor is recommended for this. Hold the resistor with pli-
ers, as the resistor may become extremely hot.
WARNING: Under load, with a sine wave signal at full
power into both channels, the amplifier may draw in
excess of 30 amperes from the AC service mains.
WARNING: Do not change the position of the Mode
Switch when the amplifier is turned on. If the position of
this switch is changed while the amplifier is powered,
transients may damage your speakers.
WARNING: Heatsinks are not at ground potential. Si-
multaneously touching either heatsink and ground, or
both heatsinks will cause electrical shock.
CAUTION: Eye protection should be worn at all times
when protective covers are removed and the amplifier
is plugged in.
CAUTION: Disconnect the power cord before install-
ing or removing any cover or panel.

5.2 General Information

The following test procedures are to be used to verify
operation of this amplifier. DO NOT connect a load or
inject a signal unless directed to do so by the proce-
dure. These tests, though meant for verification and
©2000 Crown International, Inc.
alignment of the amplifier, may also be very helpful in
troubleshooting. For best results, tests should be per-
formed in order.
All tests assume that AC power is from a regulated AC
source appropriate for the unit under test.. Test equip-
ment includes an oscilloscope, a DMM, a signal gen-
erator, loads, and I.M.D. and T.H.D. noise test equip-
ment.

5.3 Test Procedures

5.3.1 Standard Initial Conditions
Level controls fully clockwise.
Stereo/Mono switch in Stereo.
Sensitivity switch in 26 dB fixed gain position.
Ambient Temperature: 20 to 30 degrees C.
It is assumed, in each step, that conditions of the am-
plifier are per these initial conditions unless otherwise
specified.

5.3.2 Output Bias Adjustment

Spec: 310 to 330mVDC.
Procedure: Perform procedure for each channel. While
the heatsink temperature is less than 40° C measure
the DC voltage on the output module across R09 (15
ohm) or on the main module at TP100-7 (TP200-7 for
channel 2), adjust R02 if necessary. Measure the DC
voltage on the output module across R25 (15 ohm) or
on the main module at TP100-8 (TP200-8 for channel
2), adjust R33 if necessary.

5.3.3 ODEP Voltage Adjustment

Spec: 10.00V at 25 degrees C heat sink. See chart for
temperatures other than 25 degrees.
Procedure: Measure the heatsink temperature. If un-
able to do so, note the room temperature and do this
procedure while the heatsink temperature is at room
temperature.
Measure the voltage on TP100-5 and adjust R186 for
the voltage per the chart. This voltage will be a nega-
tive voltage. Measure the voltage on TP100-10 and
adjust R300 for the voltage per the chart. This voltage
will be a positive voltage. For channel 2 the designa-
tions are TP200-5, TP200-10, R286, and R400.
MA-2402 Service Manual
Maintenance 5-1