SHARP SD-AT100H
Service Manual

SD-AT100H

TO CHECK AND CANCEL PROTECT CIRCUIT DETECTION LINE
1. After power supply, the microcomputer (IC301) built in this model consecutively monitors the following errors. If any error occurs, 'Er_AP00' is displayed and all power supply except for the one to drive the microcomputer is interrupted. Abnormal output voltage drop of each regulator (below approx. 3 V) Excessive output offset of 1-bit amplifier (over approx. 2 V of DC potential) Excessive main supply current of 1-bit amplifier (over DC approx. 5.5 A) Abnormalities of cooling fan motor and its driving circuit (stop, etc.)

1 2 3 4

2. Criteria for judging errors of built-in microcomputer and checking/cancelling detection line Condition: The voltage of microcomputer pin 91 (PROTECT) lowering below 2.0 V is regarded as an error. (In the demonstration mode to stop cooling fan, the voltage of 1.2 V is regarded as an error.) Checking/Cancelling Caution: When interrupting the PROTECT detection line, the microcomputer does not operate protectively. In case of an error caused by output short-circuit of each regulator, components and board on the spot may be burnt. Do not interrupt the PROTECT detection line of the microcomputer, if any cause other than the above mentioned is not identified. (For approx. 0.5 seconds after error detection, power is supplied; power supply can be checked with an oscilloscope, etc. As leading and trailing edges of the voltage are so steep that the power supply cannot be checked by the tester.)

1 Abnormal output voltage drop of each regulator 2 Excessive output offset of 1-bit amplifier

Connect the measuring apparatus (oscilloscope, etc.) to the stabilized output of the regulator to turn on the unit power switch. If the stabilized output is far smaller (below approx. 3 V) than that shown in the circuit diagram, the regulator and the circuit to be supplied with the power may be defective.

After disconnecting the CNP705, CNP706 and CNP707 (speaker output connector of 1-bit amplifier), turn on the unit power for the normal operation. (No sound is heard from the speaker.) * After repairing, adjust the output offset voltage of 1-bit amplifier as shown on page 21. If the protective operation is observed even after disconnecting the CNP705, CNP706 and CNP707, circuits Q721 to 732 (DC voltage detection of speaker output) may be defective.

3 Excessive main supply current of 1-bit amplifier

After disconnecting the CNPE01, CNPE02 and CNPE03 (main power source connector of 1-bit amplifier), turn on the unit power for the normal operation. (No sound is heard from the speaker.) * After repairing, adjust the output offset voltage of 1-bit amplifier as shown in page 21. If the protective operation is observed even after disconnecting the CNPE01, CNPE02 and CNPE03, the circuit of Q712 to Q717 and IC701 (supply current detection circuit) may be defective.

4 Abnormalities of cooling fan motor and its driving circuit (stop, etc.)

Turn on the unit to visually inspect the cooling fan motor till the protective operation starts. * If the fan is rotating forcefully; Q520, contact of the CNP505 (connector for fan motor), or fan may be defective. (CNP505 pin 3 potential during normal fan operation is approx. 0 V.) * When the fan is not rotating or seems to be stopping. If it is checked that the CNP505 (connector for fan motor) is not defective and it is also checked by oscilloscope, etc that voltage of pin 1 (red line of fan) is approx. 6 V, the fan may be defective. When the voltage of the CNP505 pin (1) is far lower than 6 V, and base voltage of Q521 is almost the same as that shown in the circuit diagram, the fan or the circuit consisting of P501and Q523 may be defective. When the base voltage of Q523 is 0 V or extremely lower than the value shown in the circuit diagram (3.5 V), the system control terminal of Q522 may be defective.

� 35 �