Read Sharp SD-PX15H (serv.man13) Service Manual online
SD-PX15H
2 – 10
[5] Confirming and Canceling the Detection
Line of the Protect Circuit
Line of the Protect Circuit
1. When power is on, the microcomputers (IC002) installed in this
model continuously monitor the following abnormal operations. If
any abnormality occurs, all power except for the circuit driving
these microcomputers are cut off immediately.
any abnormality occurs, all power except for the circuit driving
these microcomputers are cut off immediately.
1) An abnormal drop in the regulator output voltage.
2) Excessive output offset of the 1-bit amplifier.
(Power cut off immediately after direct current potential exceeds
approx. 2 V.)
approx. 2 V.)
3) Excessive main power supply current of the 1-bit amplifier.
4) Abnormalities detected in the cooling fan motor and its drive cir-
cuit. (Stop, etc.)
Power cut off after “FAN LOCK” displayed.
2. How the microcomputers judge abnormalities and confirming and
canceling the detection line.
Conditions:
1) Abnormalities detected according to the voltages on pin 91 of
IC002 (PROTECT).
2) An abnormality detected when pulse signals input to pin 26
(FAN LOCK) of IC002 are lost for 5 sec.
3. Confirming and canceling the detection line.
CAUTION: When the above failures 1) and 2) are detected and the
detection lines (PROTECT and FAN LOCK) are discon-
nected, protection of the microcomputer does not work.
nected, protection of the microcomputer does not work.
If the cause is short circuits of regulators and the detection
lines are disconnected, the parts and PWBs may burn out.
Therefore do not disconnect these lines unless it is clear
that the cause is the failures 1) and 2).
lines are disconnected, the parts and PWBs may burn out.
Therefore do not disconnect these lines unless it is clear
that the cause is the failures 1) and 2).
(After a failure, a current is supplied for approx. 0.5 sec-
onds which can be observed with an oscilloscope. It is hard
to observe a current with a tester since rising and falling
edges are steep.)
onds which can be observed with an oscilloscope. It is hard
to observe a current with a tester since rising and falling
edges are steep.)
1) If an abnormal drop in the regulator output voltage is detected,
connect the measuring instrument (the oscillograph, etc.) to the
regulator stabilized output and then turn on the power of the set.
regulator stabilized output and then turn on the power of the set.
When the output voltage is significantly lower than the stabilized
output voltage shown in the circuit diagram, the regulator itself
and its destination circuit are doubtful.
output voltage shown in the circuit diagram, the regulator itself
and its destination circuit are doubtful.
2) Excessive output offset of the 1-bit amplifier is detected, remove
BIA103 and then turn on the power of the set for normal opera-
tion.
tion.
• After repairing, adjust the output offset voltage of the 1-bit
amplifier.
