Crown PSA-2 - Page 83

Type of Test/ Adjustment
5. Main Board Voltage
6. Output Assembly
Voltage
7. Standby Relay
8. DC Offset
9. Bias
10. Low Frequency
Protect
Il, Protection Circuit
7-15
Input Signal
Characteristics
None
None
None
SA2 - None
PSA-2-Shorting
plug in unbal-
anced input jack
None
9Hz sine wave,
variable (no load)
A. None (no
load)
B. IKHz sine
wave; 1V
Comments
5. Check voltage on test points 1, 2, 3, and 4 (of Main board
modu! ee Fig. 6.9) to ground. Voltages should be Py)
somewhere between 10.5V and 13.0V; pins | and 3 will
exhibit a negative potential whereas 2 and 4 will be positive.
If these voltages cannot be obtained, adjust to 12V via the
multiplier balance circuitry (See step 11C).
Check voltage on test pins G of each output board
assembly. At room temperature (25°C), the voltage should
be 2.98V (+.12V)
Check the operation of Re
their channel standby pins:
KI-pin “D” on power Supply Module
K2-pin “L” on Power Supply Module.
y KI and K2 by grounding
Adjust R104 and R204 so that with the input level
controls fullyclockwise, a de voltage of +10mV appears
at the output of each channel.
Adjust RN102 and RN202 so that 2.5mV appears
across pins A to C on both of the negative output modules.
Be sure the unit has had sufficient warm-up time (at least
15 minutes).
Insert a 9Hz signal into the unbalanced input of each
channel. Slowly increase the input level; note that when the
output reaches approximately 42V, the low frequency <
protect circuitry will activate. f f
A. Place a 180K ohm resistor across pins “G” and “H”
hecking the voltage at test
and 4. The voltage should vary from +12V with-
out the resistor to+4V with the resistor.
of each output module while
pins |, 2
B. When applying a 1V, IK Hz signal into both an 8
and 4 ohm load, no oscillation should be visible (via oscil-
liscope) in the output waveform. Fig. 7.21 shows a correct
waveform.
Fig. 7.21 Correct Output Waveform