QSC PLX Series, Technical & Service Manual

Page: 14 / 83

l
OUTPUT NOISE
1. Set the amplifier gain controls all the way up, with a I kHz 1.5OVrms 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.
l
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 3002 Test Procedure
l
S E T - U P
1. Connect a test load to the output terminals of the amplifier.
2. Make sure Mode Switches 1 - 10 are in the default position (1 on, 10 on, all others off).
3. 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.
4. Connect a dual-channel oscilloscope to the following test points:
Chl - a 1OX (vertical sensitivity - 2V/cm) scope probe to the channel speaker output.
Ch2 - a 1X scope probe (vertical sensitivity -
to the distortion analyzer
output.
5. Set amp gain pots fully clockwise and turn on power switch.
6. Connect the output of the signal generator to the input terminals of the amplifier and
select an output of 1.70 VRMS, 1 kHz sine wave.
7. 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.
1. Slowly raise the variac voltage and watch for excessive current draw (line current
greater than 0.5A a.c. at 60 Volts). less for Pause at 9OVAC
European) for three seconds until the mute / protect circuit disengages.
Continue to 12OVAC (240V European).,
2. Verify that the fan is operating at low speed.
3. Turn the power switch off and on a few times to verify the 3 second power-up muting
delay.
l
CHANNEL OUTPUT
1. Look for amplified signal on the scope for channel 1. Switch the input signal and scope
to channel 2 and repeat output test. Check for noisy I contaminated gain pots by
observing general instability on the distortion waveform while adjusting the gain control
levels.
10