Studio Technologies 41 2013 - Manual (Page 17)

Model 41 User Guide Issue 3, November 2013
Studio Technologies, Inc. Page 17
Maintaining Correct IFB
Output Current Draw
Each of the four IFB outputs is designed
to provide up to 220 milliamperes of DC
current. By design, the IFB outputs are
protected so that an overload condition,
or even a complete short circuit, should
not cause damage. Exceeding 220 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 IFB output volt-
age to cycle through a 4-seconds-on/10-
seconds-off sequence. Restoring the IFB
output load to be within the maximum 220
milliamperes will allow the output to again
operate normally. In extreme cases, such
as when 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 operation will again take place.
Please don’t test the Model 41’s ability to
sustain frequent 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 cir-
cuit, is being placed on one or more of
the IFB outputs. The LEDs provide a direct
indication of the IFB outputs’ DC output
voltage. Each output voltage is directly re-
lated to the amount of current being drawn,
as well as indicating when its IFB output
circuit has entered its protection mode and
has essentially shut down. During normal
operation the DC level on pin 2 of each IFB
output circuit will range from approximately
28 to 30 volts. An LED will begin to flash on
and off if the level falls below approximate-
ly 24 volts DC. This will occur when the
current draw is greater than approximately
220 milliamperes. As previously discussed,
if the fault lasts for more than four seconds
the LED will flash at a faster rate. In addi-
tion, 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 creates a partial or full
short circuit between pin 1 (common) and
pin 2 (power with audio) on an IFB output’s
XLR connector. Another cause can be due
to problems with the IFB user devices.
Either a defective user device can be draw-
ing too much current or too many user
devices end up being connected to the
same IFB output. Troubleshooting an IFB
output 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 ten seconds of
the problem being “cleared” the status
LED will stop flashing.
Determining the actual IFB output current
draw won’t often be required but can be
useful in a tough troubleshooting situation.
This measurement can be performed using
any good-quality digital multimeter. Begin
by setting the meter to measure DC cur-
rent. Then place the meter leads in series
with the pin 2 lead of the XLR connector
associated with the IFB output to be test-
ed. The easiest way to measure the pin 2
current is to create a simple adapter cable
using one female and one male 3-pin XLR
connector. Connect pin 1 on both connec-
tors together. Connect pin 3 on both con-
nectors together. Connect separate wires