Alto ELVIS10A Instrukcja serwisowa - Strona 5

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3. Test procedures & Setting

CAUTION

Before removing or installing the Power amplifier, switch off and disconnect the power cord from the AC mains socket. When you have visible

the components, discharge the capacitor before to start the maintenance.

When you connect the probe to the output of amplifier, insulated the earth of the oscilloscope, to prevent short circuit during the test.

The Power Amplifier work in Class H and use a dual bipolar rail configuration, one low rail(+/-Vcc1)RMS power and second high rail (+/-Vcc2)

IHF power.

Read the Service Manual before to proceeding to any operation.

VISUAL INSPECTION

Before to proceed with maintenance, look the condition of the product, for define the entity of the damage and probably cause.

Disconnect the power amplifier from the cabinet and look if appears an evident mechanical damage or an assembled circuit burn or break.

Verify the integrity of acoustical component, disconnect from the passive crossover and measure with a digital multi-meter the resistor of the

voice coil of the woofer Rcc=3.5/6 ohm and of the driver Rcc=6 ohm. If you measure a resistor with less value the voice coil is in short circuit,

if you measure open circuit the voice coil is break off.

OPTIMUM TEST INSTRUMENT

FUNCTION GENERATOR

DUAL-CHANNEL OSCILLOSCOPE

DIGITAL MULTIMETER

FAN LOAD RESISTORS 4 OHM/400W

VARIAC(0-250VAC)

POWER MODULE SETUP

Remove the transformer with your bracket, unscrew the 8 screw M4 without remove the electrical connection.

Fix the heat sink with PCB amplifier on the chassis with 2 screw, for prevent casual damage.

Turn full anticlockwise the knob of Main Volume, for prevent the signal noise at the Input of the amplifier.

Connect the digital multi-meter set in Vcc, across the R33=0.22R 5W, if you have a analog tester set at a correct scale and respect the polarity.

Set the trimmer VR1 used for the idle current, in full anticlockwise position, for prevent the damage of the amplifier, during the setting.

Set the VARICAL at 0VAC and connect from the 230VAC mains socket an the power amplifier under test, verify that the socket and the power

cord included the earth ground connected.

ADJUSTMENT

Switch ON the power amplifier and increase slowly with the Variac, the AC voltage until 230V.

See on the digital multi meter and read a value near to 0 mV(Vcc), turn in clockwise the trimmer VR1 until to read 5mV(+/-0.5mV) across the

R33, now wait until the temperature rise, in the same time also the voltage rise, turn in anticlockwise the trimmer VR1 until to read again

5mV(+/-0.5mV) across R33, read the same value also on R34 (+/-1mV) and verify the stability of the value, do not risk a thermal drift, repeat

the setting procedure.

When you are sure of the stability of power module, switch OFF the power amplifier disconnect the multi meter, assemble the transformer

with bracket on the chassis with at the 8 screw M4.