Studio Technologies 42A 2008 - Manual (Page 17)

Model 42A User Guide Issue 2, February 2008
Studio Technologies, Inc. Page 17
If the Model 42A Doesn’t
Work At All
A source of AC mains power must be
connected to the Model 42A. The unit
is a “universal input” type so that ap-
plying anything between 100 and 230
volts, 50/60 Hz is acceptable. Whenever
mains power is connected the four moni-
tor status LEDs should go through their
power-up routine, lighting one at a time in
sequence. If this does not occur confirm
that AC mains power is active (“hot”) and
that the cord is securely mated with the
inlet connector on the Model 42A’s back
panel.
In all foreseeable situations, both normal
and abnormal, the status LEDs should
go through the normal power-up routine.
However, it’s possible that if all four IFB
circuits are being presented with a short-
circuit condition, the internal 36 volt power
supply may enter its protection mode and
shut down. In this case no LED will light.
If this scenario occurs, even after confirm-
ing that mains power is correctly being
applied, try removing the loads from the
IFB circuits. The easiest way to do this
is to remove the 3-pin female XLR-type
connectors that may be plugged into
the Model 42A’s back and/or front panel.
If normal operation then begins, carefully
check the IFB circuit wiring for fault
conditions.
If the status LEDs still don’t go through
their power-up routine, even after con-
firming that mains power is present and
that the IFB circuits are not shorted, it’s
likely that the unit requires factory service.
For safety in the event of a major internal
failure, the internal 36 volt power supply
contains a fuse in series with the incoming
mains power. This fuse will open (“blow”)
only if a serious failure occurs inside
the unit. The fuse is not field-replaceable.
The Model 42A must be returned to the
factory, or an authorized service location,
for review and repair.
Maintaining Correct Input
Signal Levels
The Model 42A’s four 2-channel audio
inputs are designed for nominal signal
levels of +4 dBu. Applying signal levels
significantly lower than +4 dBu will re-
duce the signal-to-noise ratio (raising the
perceived noise floor) and can prevent
the connected user devices from operat-
ing optimally. Applying signal levels sig-
nificantly higher than +4 dBu will reduce
the headroom and greatly increase the
chance of reaching audio “clipping.”
Obviously, these cautions are not unique
to the Model 42A, but apply to most audio
equipment. The front-panel level meters
provide an easy means of confirming that
the Model 42A is being presented with the
correct audio levels.
To confirm correct IFB circuit operation
at locations away from where the Model
42A is installed, it’s possible to use the
Model 72 Level Meter/Interface, also
available from Studio Technologies. The
Model 72 is a compact, portable device
that plugs directly into IFB or intercom
circuits and provides two useful func-
tions. Two 5-segment LED meters display
the audio levels present on pins 2 and 3
of the connected circuit. In addition, two
“dry” line-level audio outputs are provided.
Complete information on the Model 72
is available on the Studio Technologies
website.