Orban OPTIMOD-FM 8600Si, Operating Manual

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OPTIMOD-FM DIGITAL MAINTENANCE
4-9
C) Connect the audio voltmeter to the Left Analog Output.
D) Adjust output trim VR301 to make the meter read +10.0 dBu. (0 dBu = 0.775V
rms.) Verify a frequency reading of 400 Hz.
E) Verify THD+N reading of <0.03% (<0.01% typical) using a 22 kHz low pass fil-
ter in the distortion analyzer.
F) Set the
M
ODE
to
B
YPASS
.
B
YPASS
defeats all compression, limiting, and program equalization but
retains pre-emphasis.
G) Verify a reading (noise) of <–80 dBu at the output of the unit.
H) Using VR302, repeat steps (C) through (G) for the Right Analog Output.
4. Check frequency response of Analog I/O.
A) Verify 8600Si software controls are set to their default settings. [Refer to step
(2.A) on page 4-7.]
B) Be sure you are still in
B
YPASS mode and that the
B
YPASS
G
AIN = 0.0 dB [see
step (3.F)].
C) Connect the oscillator to the Left Analog Input XLR connector.
D) Inject the Analog Input XLR connector with a level of +10 dBu with the oscilla-
tor set to 100 Hz.
This is 17 dB below the clip level, which allows headroom for pre-
emphasis. (75
μ
s pre-emphasis will cause 17 dB of boost at 15 kHz.)
E) Connect the audio analyzer to the 8600Si's Left Analog Output XLR connec-
tor.
F) Verify a level of 0 dBu ±1 dB. Use this level as the reference level.
G) Verify that frequency response at 50 Hz, 100 Hz, 400 Hz, 5 kHz, and 15 kHz is
within ±0.1 dB of the reference level. Figure 4-1 shows a typical result.
This procedure tests the analog input circuitry, the A/D converter, the
DSP, the D/A converter, and the analog output circuitry.
50 100 200 500 1k 2k 5k 10k
-400m
-200m
0
200m
400m
600m
dBrA
Hz
Figure 4-1: Typical Frequency Response, 30Hz to 15 kHz