Operating Manual - Powerflex
8.SELF-PROTECTION FEATURES
Powerflex amplifiers contain circuitry to
1.) Power supply undervoltage
2.) Power supply overvoltage
3.) Output overcurrent
4.) Heat sink overtemperature
5.) Unacceptable DC or high frequency output content
6.) AC power interruption
Except for AC power interruption, the detection of any fault will result in the activation of protection cir- cuitry on a particular module, which consists of two chan- nels. That is, a short circuit on the output of channel 1 will result in both channel 1 and channel 2 entering pro- tect mode. This is because the signal processing module, which processes both channels simultaneously, does not distinguish between the two channels within a channel pair when processing a fault.
An AC power interruption will result in all chan- nels entering protect mode simultaneously, just as if the amplifier is being turned off.
In all cases, the amplifier will restart the signal processing module after a short delay and will reconnect the speakers after several seconds if no further fault con- ditions exist. This allows the servo circuitry to bring any residual DC offsets to zero before speakers are connected.
Specific conditions resulting in a fault are as follows:
8.1Power supply undervoltage - less than about 55 volts on the either supply rail. Possible causes would
be total load on the outputs exceeding recommendations (remove some speakers - 4Ω load min, 8Ω min bridged),
low AC mains voltage (reduce extension cord length or increase wire size, or switch to an AC mains circuit more capable of supporting the amplifier's power requirements), or improper AC inlet mains voltage setting (make sure nominal AC mains voltage matches the number in the view- ing window on the AC inlet).
8.2Power supply overvoltage - more than about 92 volts on either supply rail. Possible causes would be high AC mains voltage (change to an AC mains circuit with voltage within the amplifier's stated requirements) or im- proper AC inlet mains voltage setting (make sure nominal AC mains voltage matches the number in the viewing win- dow on the AC inlet).
8.3Output overcurrent - more than 15 to 20 amps being drawn from any output. Possible causes would be total load on the affected output exceeding recommenda- tions (disconnect some speakers), or a short circuit on one of the outputs driven by the affected module (inspect speaker wiring for proper connection).
The above conditions are checked by the signal processing module on a switching cycle by switching cycle basis and are therefore monitored as often as a million or more times a second, allowing protection well before de- structive conditions have time to cause part failure.
8.4Heat sink overtemperature - a measured heat sink extrusion temperature of more than 85 to 90 degrees C. The
8.5Unacceptable DC or high frequency output content - a DC offset in the output signal of more than a few hundred millivolts indicates module failure, and will trigger a DC protect fault. High frequency (20kHz to 100kHz) in the output at high amplitudes can cause speaker damage and causes a fault condition more or less rapidly as frequency and amplitude vary.
These two conditions (DC and HF) are tested by the same circuit so the exact cause cannot be isolated. If the fault condition persists after disconnecting all inputs and outputs from the amplifier, there is probably a module failure requiring service. Note: the
8.6AC power interruption - a dropout (or brown- out of sufficient magnitude) of more than one half mains line cycle and less than one whole cycle in duration.
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