QSC PLX Series Technical & Service Manual Download Page 9

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4. Verify that the NTC circuit causes thermal shutdown after an extended period.
5. When thermal shutdown occurs, verify AC idle current of less that 0.90 amperes

C M T E S T

1. Select an 8 ohm load and confirm that this amplifier is producing rated power.

2. Check the Common Mode of the amplifier by inserting a 1/4” input jack halfway into each

channel and observe about 6

of output voltage reduction. There will also be a 180

degree phase inversion at the output of the channel under test.

OUTPUT NOISE

1. Set the amplifier gain controls all the way up, with a 1 kHz 1.3OVrms sinewave input

signal. Note the output level at full power just below clipping. Adjust gain if needed.

2. Remove the input signal connector from the amplifier and measure the residual noise

level produced into the load by the amplifier. The noise signal should be 107 dB down

from the full output power point measured. A signal to noise ratio should be better than
or equal to 107dB. Check both channels.

FINAL CHECK

This completes the amplifier test procedure for this model. Inspect the amplifier for

mechanical defects. Inspect the solder connections. Reassemble the amplifier and verify

the amplifier’s operation before returning the product to service.

PLX 1602 Test Procedure

SET-UP

5.
6.

Connect a test load to the output terminals of the amplifier.
Make sure Mode Switches

1 10

are in the default position (1 on, 10 on, all others off)

Connect a distortion analyzer with a resolution of

20-20kHz (or better) to the

output terminals of the amplifier. Enable the 80kHz low pass filter.

Connect a dual-channel oscilloscope to the following test points:

a 1 OX (vertical sensitivity 2V/cm) scope probe to the channel speaker output.

Ch2 - a IX scope probe (vertical sensitivity -

to the distortion analyzer

output.

Set amp gain pots fully clockwise and turn on power switch.
Connect the output of the signal generator to the input terminals of the amplifier and

select an output of 1.30 VRMS, 1 kHz sine wave.

Plug the amplifier into a variac and set up an AC line current monitor.

POWER UP 8 MUTE DELAY TEST

CAUTION: To avoid damage to the main printed circuit board, place a 50 ohm 225W resistor (100 ohm,
240VAC) in series with the high (+) lead on the AC cable during variac ramp up. If the switching power
supply has a shorted device at initial power up, this AC resistor pad will help prevent undue damage. After

the amplifier has been fully powered up via the variac, confirm that the amplifier has achieved

stable operation during idle. Remove AC power from the amplifier and disconnect the series
resistor for normal operation. Continue with the test & calibration process.

Slowly raise the variac voltage and watch for excessive current draw (line current

greater than 0.5A a.c at 60 Volts).

for

240V. Pause at 9OVAC

European)

for three seconds until the mute protect circuit disengages.

Continue to 12OVAC (24OV

European).

Verify that the fan is operating at low speed.