Crown ce 4000, Service Manual

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CE 4000 Service Manual
Maintenance 4-10
130485-1 Rev. B
©2002 Crown Audio, Inc.
Figure 4.18 Correct Overlap Adjustment
(Less than 10V)
4.6.9 Crosstalk at 20 kHz
Spec: Greater that 50 dB.
Procedure: Load each channel to 8 ohms. Verify that
both gain switches are set at 26 dB and both level
controls are at full volume. Inject a 2.0 Vrms, 20 kHz,
sine wave into channel 1 and terminate channel 2
with 600 ohms. Measure less than 126.5 mV at the
output of channel 2. Now remove the signal from
channel one and inject it into channel 2. Terminate
channel 1 with 600 ohms. Measure less than 126.5
mV at the output of channel 1.
4.6.10 Post Test Settings
After completion of testing, if all tests are satisfactory,
the amplifier controls should be returned to the
positions required by the customer. If the conditions
are unknown or unspecified, the factory settings
are as follows:
• Gain switches set to 1.4 V
• Bridge Mono switch turned off
• Level controls set fully counterclockwise
• Power switch turned off
• All fi lter switches set to the fl at position
4.7 Calibrations
4.7.1 Gaussian Filter Calibration
Procedure 1:
Obtain a multimeter with decibel
measurement capabilities. Set the multimeter to dB
measurement mode. Insert a 1 kHz signal into the
input and measure at pin 14 of U111D. Reset the
meter to 0 dB using the 1 kHz signal as a reference
signal. Increase the signal generator frequency
to 20 kHz, leaving the output level unchanged.
While measuring pin 14 of U111D adjust R178 for
a reduction of level by 2.6 dB (readout should be
–2.6 dB).
Procedure 2: Obtain a multimeter with decibel
measurement capabilities. Set the meter to dB
measurement mode. Insert a 1 kHz signal into the
input and measure at the speaker output (no load).
Reset the meter to 0 dB using the 1 kHz signal as
a reference signal. Increase the signal generator
frequency to 12.5 kHz, leaving the output level
unchanged. Adjust R178 for a meter reading of 0 db.
This second test method is an alternative to the fi rst
and should give the desired results: a fl at frequency
response throughout the audio bandwidth.
4.7.2 Overlap Correction and Adjustment
Conditions:
• Amplifi er output assembly MUST be room tem-
perature (72 degrees F/21 degrees C)
• No input signal
• No load
Procedure: Monitor TP37 found on the Main PWA.
Center oscilloscope to view lower right portion of
waveform (see Figure 4.17). Adjust R170 for the
sharpest-possible squarewave rising edges, with a
transition curve less than 10.0V. Figure 4.18 shows a
correct transition curve, Figure 4.19 shows “underlap”
(under adjustment), where the transition curve
exceeds 10.0V. Figure 4.20 shows “overlap” (over
adjustment), where the transition curve is not
“smooth.”
Repeat for channel 2, monitoring TP244 and adjusting
R270.
10V
Transition
Figure 4.17 Overlap Adjustment