SD-CX1 (serv.man5). Part 2 - text (Page 12-36) - Sharp Audio Service Manual (repair manual). Page 7

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1. After power supply, the microcomputer (ICD01) built in this model consecutively monitors the following errors 1 to 4.  If any error

occurs, 'Er_AP00' is displayed and all power supply except for the one to drive the microcomputer is interrupted.
1 Abnormal output voltage drop of each regulator

(below approx. 3 V)

2 Excessive output offset of 1-bit amplifier

(over approx. 2 V of DC potential)

3 Excessive main supply current of 1-bit amplifier

(over DC approx. 5.5 A)

4 Abnormalities of cooling fan motor and its driving circuit

(stop, etc.)

2. Criteria for judging errors of built-in microcomputer and checking/cancelling detection line

Condition: The voltage of microcomputer pin 7 (PROTECT) lowering below 3.5 V is regarded as an error.
(In the demonstration mode to stop cooling fan, the voltage of 1.5 V is regarded as an error.)

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.)

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 CNPV99 (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 24.

If the protective operation is observed even after disconnecting the CNPV99, circuits QV95 to 98 (DC voltage detection of
speaker output) may be defective.

After disconnecting the CNP801 (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 30.

If the protective operation is observed even after disconnecting the CNP801, the circuit of ICV98/ICV99 (supply current
detection circuit) may be defective.

Turn on the unit to visually inspect the cooling fan motor till the protective operation starts.

* If the fan is rotating forcefully;

QV94, contact of the CNPV97 (connector for fan motor), or fan may be defective. (CNPV97 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 CNPV97 (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 CNPV97 pin (1) is far lower than 6 V, and base voltage of QV93 is almost the same as that shown
in the circuit diagram, the fan or the circuit consisting of PSV801, QV85, QV87, and QV93 may be defective.

When the base voltage of QV85 is 0 V or extremely lower than the value shown in the circuit diagram (3.5 V), the system
control terminal of SOV90 may be defective.