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SD-AT1000W
TO CHECK AND CANCEL PROTECT CIRCUIT DETECTION LINE
1: In this model the microcomputer (IC701) detects the following malfunctions once power is supplied, and cuts off power from all the parts except for the circuit driving the microcomputer. Abnormal drop in the output voltage of each regulator (below approx. 1.5 V) Power is cut off instantly without display. Output offset over voltage of the 1-bit amplifier (above approx. DC 2 V) Mains overvoltage of the 1-bit amplifier (above approx. DC 5.5 A) Power is cut off instantly without display. Defects in the cooling fan or its drive circuit (when stopped) Power is cut off after �FAN LOCK� is displayed. Abnormal overvoltage or undervoltage of power supply. Power is cut off instantly without display if voltage is abnormal.
1 Abnormal drop in the output voltage of each regulator
Connect a measuring device (such as an oscilloscope) to the stabilizing output of the regulator, and turn on the unit. If the detected voltage is extremely lower than the voltage on the circuit diagram (below approx. 1.5 V), the regulator itself or the circuit is defective.
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2 Output offset overvoltage of the 1-bit amplifier
Adjust the voltage of the output offset. If a protective operation is still activated, ICA401 on the 1-bit amplifier could be defective (the detection circuit of the speaker output DC voltage).
2: Criteria for abnormality, and checking and cancelling the detection line The criteria: The voltage of pin 2 (PROTECT) on IC701. The voltage of pin 7 (OFFSET) on IC701: Low (below approx. 1 V) (abnormal) and High (above approx. 2.5 V) (normal) . Detected as abnormal if a pulse signal is not input into the pin 1 (FAN LOCK) for 5 seconds. Detected as abnormal if the voltage of the pin 3 (+B CHECK) is lower than 1.2 V or higher than 3.0 V.
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Checking and cancelling the detection line: Caution: If the PROTECT/OFFSET detection line is disconnected in case of or above, a protective operation does not function. The disconnection by output short-circuit of each regulator may cause the parts or PCBs to burn out and therefore do not disconnect the detection line when the cause is not identified. (Power supply can be detected with an oscilloscope or like during approx. 0.5 seconds after an abnormality is found. Note that the detection would be difficult with a tester as the voltage rises and falls rapidly.)
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