Hitachi RAM-40QH5 Service Manual page 38

(5) C001 to C005, NF COIL 1
There absorb electrical noise generated during
operation of compressor, and also absorb
external noise entering from power line to protect
electronic parts.
(6) Surge absorber, varistor 1, 2, 3
These absorbs external power surge.
(7) Inrush protective resistor (R002, R003)
This works to protect from overcurrent when
power is turned on.
2. Indoor/Outdoor Interface Circuit
The interface circuit superimposes an interface signal on the 35V DC line supplied from the outdoor unit
G
to perform communications between indoor and outdoor units. This circuit consists of a transmiting circuit
which superimposes an interface signal transmit from the micro computer on the 35V DC line and a
transmiting circuit which detects the interface signal on the 35V DC line and outputs it to the micro
computer.
Communications are performed by mutually transmiting and receiving the 4-frame outdoor request signal
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one frame of which consists of a leader of approx. 100 ms., start bit, 8-bit data and stop bit and the
command signal with the same format transmit from the indoor unit.
From outdoor microcomputer to indoor microcomputer
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The request signal output from microcomputer pins
circuit outputs an approx. 38kHz high-frequency signal via pin
according to the request signal. This high-frequency signal is amplified by a transistor, superimposed on
the DC 35V line via C801, C811 and L801, L802 and supplied to the indoor unit.
To prevent erroneous reception, the outdoor microcomputer is designed so that it cannot receive a signal
while it is outputting a request signal,
The receiving circuit in the indoor unit consists of a comparator and transistor. The interface signal from
the outdoor unit on the DC 35V line is supplied to C821, where DC components are eliminated, and is
then shaped by the comparator. The shaped signal is detected by diode, amplified by amp, and supplied
to receiving input of the indoor microcomputer.
k
Fig. 2-2 shows the voltages at each component when data is transferred from the outdoor microcomputer
to the indoor microcomputer.
Indoor micro computer to outdoor micro computer
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The communications from the indoor micro computer to the outdoor micro computer are the same.
Fig. 2-3 shows the voltages and waveforms at each circuit.
❈ Be sure to ground outdoor unit.
If not grounded, noise filter circuit does not
operate correctly.
❈ If outdoor unit is not grounded, "sugar absorber",
"varistors 1 and 3" do not operate.
Be sure to perform grounding.
< Reference >
When inrush protective resistor is defective, diode
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stack may malfunction. As a result, DC voltage is
not generated and no operation can be done. In this
case, 3A fuse may have been blown.
is input to the transmitting circuit. The transmitting
X
and continues the output intermittently
!
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