Studio Technologies 76B 2012 - Manual (Page 39)

Model 76B/77B User Guide Issue 3, August 2012
Studio Technologies, Inc. Page 39
for Surround
exceeds its nominal operating voltage
range, electromechanical relays maintain
a short-circuit condition on the monitor
outputs. After the input voltage is recog-
nized as valid, a short delay takes place
before the relays are allowed to function
normally. Whenever the AC mains input
drops below its nominal operating voltage
range, the relays immediately go to their
mute state. During testing it was found
that upon power up the monitor outputs
remained very quiet; during power down a
small to moderate “tick” was the worst that
was heard.
Model 76B to Model 77B
Connections
Figure 6 gives a detailed description of
the signals that connect the Model 76B
Central Controller to the one or more
Model 77B Control Consoles. The Model
76B provides a +12 volt DC power source
for use by the Model 77B’s circuitry. The
DC output is current-limited to minimize
the chance that a short-circuit condition
will damage the Model 76B’s circuitry. An
asynchronous, bi-directional, data inter-
face links the connected units. The RS-485
hardware connection scheme operates at
a rate of 115.2 kbit/s and uses an 8-N-1
data format. The Model 76B communicates
with each Model 77B unit 20 times per
second, receiving button and rotary level
control information and sending LED and
4-digit display status data.
Mono-to-Center Polarity
It’s worthwhile to note that a polarity inver-
sion takes place whenever the stereo to
mono downmix function is active. By de-
sign, the left (L) and right (R) input signals
experience a 180-degree inversion in
the Model 76B’s combining circuitry. This
should not cause a problem as monitoring
audio signals over a single loudspeaker is
considered polarity insensitive. Only during
electrical testing would this condition be
detected.
Power-Up Messages and
Error Codes
Upon mains power being applied to the
Model 76B all connected Model 77B units
will go through a power-up sequence.
The sequence starts by each of the indi-
vidual LEDs lighting in a “walk-through”
sequence. At the same time the 4-digit
display tests all its LED segments. Then,
a set of messages provide details on the
specific Model 77B and connected Model
76B software versions:
1. Displays 77b
2. Displays Model 77B’s software version
3. Displays Model 77B’s unit address
(A1, A2, A3, or A4)
4. Displays 76b
5. Displays Model 76B’s software version
After a successful system power-up
sequence normal operation will then com-
mence. Should a problem be encountered
during power up an error code may show
on the Model 77B’s 4-digit display. If Err1
displays it indicates that communication is
not taking place with the Model 76B. The
most likely cause would be incorrect wir-
ing of the data pair linking the two units.
This could be caused by one or both of the
wires being open (not connected) or the
data pair being reversed.