Protect Circuit Explanation - Sharp Sd-As10H(S) Service Manual

[6] Protect Circuit Explanation

<Function>
DC Offset Det.
1
Over Current Det.
2
Temp Over Det.
3
DC Offset/Over Current Circuit at output short before Power ON
4
DC Offset/Over Current Circuit at output short after SP Relay ON
5
Temp Over Circuit
6
<Detail>
1. When DC level is unbalance between Lch and Rch, transistor
QA409 turn on and drive
4
Unbalance Condition:
Normally, QA409 "B" and "E" is same voltage.
When one SP OUTPUT (R+, R-, L+ or L-) is short to chassis,
-2 point voltage is half (1/2 x SP OUTPUT DC LEVEL).
1
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
1
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
µcom detect "1-BIT PROTECT" is low, then µcom 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
1
When short to other polarity output, VBB line current is so much.
, circuit.
5
.
4
.
5
Resistor RA415 voltage drop is much.
Circuit QA400 drive circuit
2
QA424 ON > QA408 ON > +D5V is supplied to QA423 BASE >
QA423 ON > QA420 ON > ICA100 RESET (21 pin) low > SLA5515
output FET OFF > Short current OFF.
QA423 ON > Pull QA408 BASE current – – – This circuit is latch.
When QA424 change off, this latch circuit keep "QA408 ON &
QA423 ON".
So, "QA420 ON > ICA100 RESET (21 pin) low > SLA5515 output
FET OFF > Short current OFF" is keeped.
Then µcom detect "1-BIT PROTECT" by QA410 or QA420 and
change into power off mode.
This circuit work is controlled by QA427 & QA411.
+D5V is supplied at speaker relay on only. Because prevent fault
action.
-1,
1
protect response is faster than µcom "1-BIT PROTECT"
Circuit
5
detection.
µcom "1-BIT PROTECT" detection expend long time.
6. When set temperature rise, circuit
QA412.
QA412 ON > QA413 ON > µcom detect "PROTECT" > µcom
change into power off.
<Attention>
: Don't mistake capacitor CA193, CA192 0.001µF.
1
When capacitance is more large, response is delay.
Can't PROTECT IC.
/ : Confirm fault action at high temperature aging.
3 6
Don't work at aging.
This circuit work at abnormal condition.
: Confirm work at (L-) or (R-) short to chassis.
4
: Confirm work at short after speaker relay on.
5
Confirm latch circuit – – – We already confirmed this circuit by your
DC voltage information (Result is OK).
1
-2
1
RA148
5.6K
RA146
5.6K
2 – 8
.
5
work to drive circuit
3
RA147
5.6K
1 2 1 2
DA337
KDS121E
3 3
RA354
33K
QA409
KTA1504 GR
DA338
2
RA415
0.1
(2W)
RA409
560
RA406
1K
QA400
KTA1504 GR
SD-AS10H
6
RA149
5.6K
-1
1