Crown PSA-2 - Page 84

t
Type of Test/ Adjustment
Multiplier Balance
Temperature Computer
Anti-pop Circuit
(earlier PSA-2/
SA units have this
circuit on separate
module. Later amps
include this circuit on
Main Module).
Display Module
(PSA-2/ PSA-2X)
Display Module
SA2/PSA-2D
PSA-2DX)
Power
crown
Input Signal
Characteristics
C. 100Hz sine
wave; variable
(no load)
D. 10Hz sine
wave; 30V output
level with 4 ohm
load
IKHz sine wave;
2V_ no load
A. [KHz sine
wave; variable
no load
B. IKHz sine
wave; variable
no load
A. IKHz sine wave,
2Vrms; 8 ohm load
B. IK Hz sine wave,
2V; 8 ohm and induc-
tive (159uh) load
C. IKHz sine wave,
2V; 4 ohm load
Comments
C. This adjustment must be made if and only if the protec-
tion circuitry (steps 11A, B) is not functioning properly.
Apply the input signal to full output (without a load) with-
out clipping the signal. Adjust R124 and R224 for minimum
signal null at test pins 1, 2, 3 and 4 on main board module
(scope should be set at 100mV for proper viewing). Repeat
steps I1A, B; proceed to step 11D.
D. Measure the AC voltage across C112, C212, C113,
C213, C114 and C214 with a true RMS meter. This may be
done by measuring across the proper pins of RN103, RN203
(see schematic).
Across: C112/C212 measure .4VAC +10
C113/213 measure 1.7VAC +10%
C114/214 measure .036 +10%
If these measurements cannot be obtained, a problem
exists in the thermal computer circuitry.
Observe the output of pins M and U on the Main
Module while turning the unit on and off several times. A
spike should be noticable upon each turn-on.
Observe the signals at the output terminals. They should
not exhibit any spike during turn-on.
A. Increase input level until the green “Signal” presence
indicators illuminate. The voltage level should be approx-
imately 1.2 volts peak at the output. Connect an oscilliscope
to the amplifier output. Again raise the input level to the
point
just
before
clipping
is
observed.
Note
the
IOC
indicators; they should illuminate prior to the visible clip-
ping point on the scope.
B. Vary input level, noting upward progression of
ladder display proportional to the input signal variance.
Connect an oscilliscope to the amplifier output. Raise the
input level to the point just before clipping is observed.
Note the IOC indicators, they should illuminate prior to
the visible clipping point on the scope.
A. 44V minimum should be obtainable before clip.
B. 20V minimum should be obtainable before clip.
C. 41V minumum should be obtainable before clip.
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