Description On The Circuits Of The 1-Bit Unit (See The Wiring Diagrams On Pages 6-23, 6- 24.); Confirming And Canceling The Detection Line Of The Protect Circuit - Sharp Sd-As10H(S) Service Manual

SD-AS10H
[4] Description on the Circuits of the 1-Bit
Unit (See the wiring diagrams on pages 6-
23, 6-24.)
1. Input Part
Signals input from BIA201 are input to the AD conversion IC (ICA100,
ICA200 and ICA300) coupled by "CA100, CA200 and CA300" and
"CA101, CA201 and CA301".
2. Modulation 1-Bit Converter
Signals input to the AD conversion ICs (ICA100, ICA200 and ICA300)
are converted into 1-bit signals for differential output. For detailed
description of the conversion into 1-bit signals, refer to the Technical
Manual for SM-SX100 already published.
3. Low Pass Filter Circuit
The 1-bit signals switched at the output ICs (ICA101, ICA102, ICA201,
ICA202, ICA301 and ICA302) are converted into analog signals by
passing through the low pass filter consisting of LA104 to LA107,
LA204 to LA207, LA304 to LA307 and CA114 to CA117, CA214 to
CA217, CA314 to CA317.
The property of low pass filter is flat up to 20 kHz and attenuated at
approx. 40 kHz by approx. 3 dB.
4. Dynamic Feedback Circuit
The 1-bit signals switched at the output ICs (ICA101, ICA102, ICA201,
ICA202, ICA301 and ICA302) are amplified between plus power and
GND.
By resistive division, the 1-bit signals pass through 75 kΩ of NF resis-
tance (RA155 to RA158, RA255 to RA258, RA355 to RA358) and are
fed back to the AD conversion IC (ICA100, ICA200, ICA300). P-P volt-
age at this time is approx. 5 V.
[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.
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