Crown CE-1000A Service Manual page 21

Rev. D
Type of Test
or Adjustment
12. Noise
13. Crosstalk Check
14. Fan Operation
CE Series Service Manual
Input Signal and
Load Parameters
No Signal
No Load
20-kHz Sine Wave
8-ohm Load
1-kHz Sine Wave
4-ohm Load
Comments
Make sure the sensitivity switch is in the 26-dB posi-
tion and the level controls are fully clockwise. Terminate
the input with a 600-ohm load. Using a 20 to 20,000- Hz
bandpass filter, measure the noise on the output of the
channel under test. Noise is measured relative to power
output at 8-ohms (275 Watts (46.9 Vrms) for CE1000,
400 Watts (56.6 Vrms) for CE 2000) and should be at
least 100-dB down from these numbers.
Make sure the sensitivity switch is set in the 26-dB posi-
tion. Load each channel to 8-ohms. Insert a 20-kHz sine
wave into channel 1 and adjust for 44.7 Vrms output.
Terminate channel 2 input with 600 ohms. Measure less
than 80 mVrms at the output of channel 2. (Greater than
55 dB down at 20-kHz)
Move the input signal from channel 1 to channel 2 and
the 600-ohm termination from channel 2 to channel 1.
Ensure there is 44.7 Vrms at the output of channel 2.
Measure less than 80 mVrms at the output of channel
1.
Make sure the mode switch is in the "stereo" position.
Plug a 1-kHz source into channel 1, 2 or both and ob-
serve the amplifier outputs with a voltmeter. Set the
inputs so that about 10 Vrms is on the outputs and set
the load to 4-ohms. If the amplifier produces power
until the heatsinks get so hot that a channel goes into
thermal protection, the fan is not working correctly. With
the amplifier still in thermal protection, measure the
voltage at J4 pin 1 (the red fan wire). If this voltage is
greater than 20VDC, there is a problem in the wiring of
the fan, or a problem with the fan itself.
If the voltage is less than 20VDC, then the fan control
circuit needs attention.
U106 is a thermally controlled current source that is
thermally connected to the heatsink. For channel 1,
R190 develops a voltage across it due to this current,
and this signal is OR'ed with the voltage from channel
2 and the transformer thermal switch. U4A is a DC
amplifier that voltage amplifies the signal, and Q1 and
Q2 current amplify this signal to drive the fan.
If the heatsinks are hot, and U4-7 is negative, suspect
U106, R191, R190, D119, R20, R21, R22, and U4. If
the heatsinks are hot, and U4-7 is positive but U4-1 is
low, suspect R23, R12, R11, and U4. If U4-1 is quite
high (above 10V), but J4-1 is not the same voltage,
Q1, Q2, R14, or R15 may be at fault.
Maintenance 2-8