Sharp SD-AS10, Руководство по обслуживанию

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SD-AS10
2 – 7
[5] Confirming and Canceling the Detection
Line of the Protect Circuit
1. When power is on, the microcomputers (IC701) 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.
1) An abnormal drop in the regulator output voltage.
(Power cut off immediately without any display when the voltage
falls below approx. 1.5 V.)
2) Excessive output offset of the 1-bit amplifier.
(Power cut off immediately after direct current potential exceeds
approx. 2 V.)
3) Excessive main power supply current of the 1-bit amplifier.
(Power cut off immediately without any display when direct cur-
rent exceeds approx. 5.5 A.)
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
IC701 (PROTECT).
2) An abnormality detected when pulse signals input to pin 93
(FAN LOCK) of IC701 are lost for 5 sec.
3. Confirming and canceling the detection line.
CAUTION: Even if abnormalities mentioned in steps 1) and 2) above
are detected, the microcomputers do not operate protec-
tion when their PROTECT lines are cut off. In the case of
abnormalities caused by short circuit of the regulator, parts
or PWBs may burn out. Do not cut off the detection line if
short circuit is not detected.
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.
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.
2) Excessive output offset of the 1-bit amplifier is detected, remove
CNPA402 and then turn on the power of the set for normal oper-
ation.
• After repairing, adjust the output offset voltage of the 1-bit
amplifier.
[6] Protect Circuit Explanation
<Function>
DC Offset Det.
Over Current Det.
Temp Over Det.
DC Offset/Over Current Circuit at output short before Power ON
DC Offset/Over Current Circuit at output short after SP Relay ON
Temp Over Circuit
<Detail>
1. When DC level is unbalance between Lch and Rch, transistor
QA409 turn on and drive , circuit.
Unbalance Condition:
Normally, QA409 “B” and “E” is same voltage.
When one SP OUTPUT (R+, R-, L+ or L-) is short to chassis, -1,
-2 point voltage is half (1/2 x SP OUTPUT DC LEVEL).
So, QA409 turn on.
When Lch and Rch are short to chassis at same time, this circuit
don’t work.
Because unbalance condition is not happened.
2. When VBB line current is so much, resistor RA415 voltage drop is
much.
So, QA400 turn on.
3. Posistor PSA405 resistance value increase at high tempature.
So, DA415 anode voltage is decreased.
4. Refer to CHART “1”
This is normal timing chart at 1-bit amp. part of AS10.
SP OUTPUT DC LEVEL is about 0V
→
6V
→
20V at timing A
→
B
→
C, D.
This circuit work at timing A
→
B change.
This timing is speaker output short to chassis before power on.
Speaker output is only (L-) and (R-).
(L+) and (R+) is through speaker relay point.
So, no concern this short at power on timing.
When short to chassis, DC level is unbalance at timing B.
Circuit QA409 drive circuit .
QA422 ON > QA421 OFF > QA420 ON > ICA100 RESET (21 pin)
low > SLA5515 output FET OFF > Short current OFF.
“QA420 ON” continue until “1-BIT PROTECT” able timing, then
µ
com detect “1-BIT PROTECT” is low, then
µ
com change into
power off mode.
5. Refer to CHART “1”
This is normal timing chart at 1-bit amp. part of AS10.
SP OUTPUT DC LEVEL is about 0V
→
6V
→
20V at timing A
→
B
→
C, D.
This circuit work at timing D.
This timing is speaker output short to chassis or other polarity out-
put after speaker relay on.
When short to chassis. DC level is unbalance at timing D.
Circuit QA409 drive circuit .
When short to other polarity output, VBB line current is so much.
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