Crown PSA-2 - Page 87

Input Signal
Type of Test/ Adjustment Characteristics
PSA-2 Balanced Input
Module
20. Test Tone Generator None
Comments
In order to make proper repairs/ adjustments with the
PSA-2 balanced input module, it is necessary to remove
the control panel plate and utilize an extender card (CPN
M 20149-7).
adjustments.
This allows ea
y access to all controls and
Note: Be sure to block air passage of the
Balanced Input Module cut-away hole with a small piece
of cardboard to ensure proper cooling during lengthy
adjustments.
Adjust all common mode ction potentiometers (R101,
R201, C102, C202) to mid rotation. Set all filter
switches (SW100, SW200, SW101, SW201) to flat. Adjust
Threshold control (R7) fully clockwise. While observing
the output (of the amplifier), hold the Test tone switch
(SWI) on. Observe 60 volt spikes, one positive then one
negative at the rate of 50 spikes per second (25 Hertz; Fig.
7.26).
Fig. 7.26 Test-Tone Output Waveform
21. Compressor D.C.
Balance
None applied to
balanced XLR inputs;
5SHz sq. wave applied
to pin one of U6 (5-
15V p-p)
22. Compressor Action IKHz sine wave;
applied to pins 2 and 3
of balanced input;
no load
7-19
Apply a 5Hz square wave (5-15V p-p with a DC offset
so that the most positive level is +15 volts) to pin | of U6.
Adjust channel | compressor DC balance control (R116)
for minimum signal at amplifier output. Perform the same
adjustment with channel 2 however, apply the signal to pin
14 of U6 and adjust R216
should be less than | volt
Amplifier output for both
Make sure that when GAIN ADJ (R106, R206) is slowly
increased, that the voltage also increases smoothly until
clip level is reached (about 44VRMS).
increased further, the output voltage should remain con-
As the control is
stant and then, increase once again. The exact range of
compression can be measured by turning the gain adjust
control fully clockwise and measuring the input voltage
verses output voltage (see performance graph, Fig.
RVW.17)
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