Studio Technologies 41 2007 - Manual (Page 17)

Model 41 User Guide Issue 2, February 2007
Studio Technologies, Inc. Page 17
To confirm correct IFB circuit operation
at locations away from where the Model
41 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.
Maintaining Correct IFB
Circuit Current Draw
Each of the four IFB circuits is designed
to provide up to 200 milliamperes of DC
current. By design, the IFB circuits are
protected so that an overload condition,
or even a complete short circuit, should
not cause damage. Exceeding 200 mil-
liamperes for more than a few seconds will
typically cause the auto shut down mode
to become active. A continuous overload
condition will cause the output voltage to
cycle through a 4-seconds on, 10-seconds
off sequence. Restoring the output load to
be within the rated 200 milliamperes will
allow the output to again operate nor-
mally. In extreme cases, such as where
the Model 41 is located in an environment
with elevated temperatures, a few minutes
may be required from the time an overload
condition is removed to when normal op-
eration will again take place. Please don’t
test the Model 41’s ability to sustain fre-
quent overload or short-circuit conditions!
The long-term reliability of the unit can be
impacted by the stress caused by these
fault conditions.
The four status LEDs make it simple to
know if an excessive load, or a short circuit,
is being placed on one or more of the IFB
circuits. The LEDs provide a direct indica-
tion of the IFB circuits’ DC output voltage.
Each output voltage is directly related to
the amount of current being drawn, as well
as indicating when its output circuit has
entered protection mode and essentially
shut down. During normal operation the DC
level on pin 2 of an output circuit will range
from approximately 28 to 30 volts. An LED
will begin to flash on and off if the level falls
below approximately 24 volts DC. This will
occur when the current draw is greater than
nominally 200 milliamperes. As previously
discussed, if the fault lasts for more than 4
seconds the LED will flash at a faster rate.
In addition, the DC output will shut down
for a 10-second period.
There’s really only one piece of advice
when it comes to understanding how
to use the under-voltage status LEDs: if
they’re flashing there’s a problem that must
be corrected! The most likely cause will be
a wiring fault that causes a partial or full
short circuit between pin 1 (common) and
pin 2 (power with audio) on the IFB circuit’s
XLR-type output connectors. Another cause
can be due to problems with the IFB user
devices. Either a defective user device can
be drawing too much current, or too many
user devices end up being connected to
the same IFB circuit. Troubleshooting an
IFB circuit problem should prove quick and
easy. Begin by disconnecting the IFB user
devices. Observe the status LED and see if
the problem has gone away. If not, review
the interconnecting cables and find the
fault condition. Within 10 seconds of the
problem being “cleared” the status LED
will stop flashing.