Hitachi RAM-60QH4 Manuel De Service page 72

(5) C001 to C011, NF COIL 1
These 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)
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 to perform
communications between indoor and outdoor units. This circuit consists of a transmiting circuit which superimposes an
interface signal transmit form 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 one frame of which
consists of a leader of approx. 100ms., 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
The request signal output from microcomputer pin
approx. 38kHz high-frequency signal via pin
high-frequency signal is amplified by a transistor, superimposed on the DC 35V line via C801 and L801, 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
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
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, "surge absorber",
"varistors 1 and 3" do not operate.
Be sure to perform grounding.
<Reference>
When inrush protective resistor is defective, diode
stack2 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. Take care.
is input to the transmitting circuit. The transmitting circuit outputs an
and continues the output intermittently according to the request signal. This
– 84 –
of the indoor microcomputer.