QSC Audio CX Series - Manual (Page 11)

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• If the fan is not running at full speed, or the channel does not reset to normal after a cool-down period,
the muting is probably because of a DC fault or other amplifier failure, especially if the “SIGNAL” or
“CLIP” indicators are lit even with the attenuator turned all the way down.
PROBLEM: Overheating
• The thermal management system on a CX Series amplifier features a two-speed fan that
modulates the cooling air flow over the heatsinks in response to the cooling needs.
If the air flow is blocked, however, or if the amplifier is overdriven into very low
impedance loads, the amplifier could overheat even though the fan is running at full
speed.
CX4 & CX4T
• At 85½ C both channels will mute. The “POWER” LED will remain lit, although the “CLIP” indicator will
be dark. The amplifier will remain this way until the temperature drops to a safe level.
CX6, CX6T, CX12 & CX12T
• At 85½ C, the channel’s output relay will mute the output. The channel will remain muted until the
temperature drops to a safe level. Even while the channel is muted, the “SIGNAL” and “CLIP” indicators
will function normally. If the “CLIP” indicator is flashing or continuously lit, reduce the gain to hasten
the cool-down and prevent repeated thermal shutdowns.
PROBLEM: Hum in the audio
• Because of its grounded-collector output transistor configuration, which maximizes thermal efficiency,
the signal ground on a CX amplifier cannot be lifted. The amplifier’s balanced inputs are meant to reject
hum, but if hum remains a problem, check the tightness of the two mounting screws on the input panel
(except CX4 and CX4T); if they are loose, the panel itself might not be well grounded to the chassis.
If you have any problems with these screws, contact the QSC Technical Services Department. In some
cases, such as when the audio signal cables are routed near lighting dimmers that use triacs, you may
need to use input isolation transformers because of the extremely high noise field produced by the
dimmer circuitry. See the paragraphs on Open Input Architecture for further information on input
transformers.
OPEN INPUT ARCHITECTURE ™ LEVEL I (CX6, CX6T, CX12 and CX12T only)
On the rear of a CX amplifier are an upper and a lower input panel; both are easily removeable for future upgrades.
This is the concept of Open Input Architecture, and the opening in which the panels mount is called the “slot.”
As installed at the factory, the lower is the CX standard input panel and the upper one is a blank. A ribbon cable
connects the “slot” panels to the rest of the amplifier. It carries input signals, speaker output monitor signals,
muting status, and clip activity; these are for supporting future accessories and remote control systems. Although
the physical dimensions of the CX, MXa, and EX panels are the same, their internal cabling is different and the
CX platform supports most (but not all) of the MXa functions but doesn’t support all of the EX functions. The
CX and MXa Open Input Architecture slot thus is designated as “Level I” and the EX as “Level II.”
Tightening input panel
mounting screws