MACKIE M1200/M1400 - Manual (Page 13)

13
The M•1200/M•1400
amps draw their ventila-
tion air in from the front
and out through the side
panels. The amp needs
plenty of fresh air to stay cool. DO NOT BLOCK
THE VENTILATION PORTS. See “Thermal
Considerations”
.
SHORT
If this LED comes on, the M•1200 or
M•1400 has detected a short circuit in either
of the outputs, meaning that the hot (+) and
cold (–) speaker wires are touching, or a
speaker itself is shorted out. Such a condition
causes the M•1200/M•1400 to engage its
PROTECT
mode (when a signal is present),
muting all signals at the amp’s outputs.
This short-circuit LED is a Mackie exclusive
(until the other guys “borrow” the idea) and
can save precious minutes of your trouble-
shooting time. Without it, you’d still have
speaker and amp protection (via the
PROTECT
circuit), but you wouldn’t be able to determine
the source of the problem. But with the
SHORT
LED, the M•1200/M•1400 comes right out and
tells you!
WARNING: The SHORT LEDs indicate an
unsafe condition for the power amplifier. Once
the
SHORT LED is lit, you must turn the power
off, wait for the indicator to extinguish, and
turn the power back on again to reset the am-
plifier.
Typical causes for a “short” indication would
be either a shorted speaker cable or too many
speaker cabinets connected to the amplifier
(i.e., the load impedance is too low). If a “short”
is indicated, please check your cables. If the
cabling is OK, then reduce the number of cabi-
nets driven by the amplifier.
ON
OFF
POWER
PROFESSIONAL POWER AMPLIFIER
If the OL (Overload) LED
is blinking frequently or
continuously, turn down
the source signal (i.e. the
mixer’s master faders).
SIG
SIG (short for “signal present”) is the lowest
step in the meters’ ladder. It senses the signal
prior to the GAIN control, so when SIG is lit,
you know the M•1200/M•1400 is receiving signal.
If it’s the only meter LED lit (meaning the other
meter LEDs are not lit), the M•1200/M•1400 is
receiving a very weak signal (below –20 dB).
PROTECT
If the PROTECT LEDs are on, the M•1200/
M•1400’s output section has shut down. That,
of course, means you won’t hear anything until
you rectify the situation. Three things can
cause the
PROTECT circuit to engage:
1. Powering up the M•1200/M•1400. A built-
in delay circuit saves your speakers (and
ears) from the thumps or pops that can
sometimes occur when powering up a
system. During this 3 second delay, the
PROTECT LEDs light up.
2. A short circuit (or near short) in either of
the outputs. Both the PROTECT and the
SHORT LEDs light up.
3. The temperature in the M•1200/M•1400
has risen to an unsafe level. The PROTECT
and the TEMP STATUS LEDs light up.