Interface Circuit - Hitachi RAF-35NH5 Service Manual

. Interface Circuit

The function of the interface circuit is to perform:
●
Communications between the indoor and outdoor units by mean of superimposing an A.C. signal (f=38kHz, amplitude 1V)
on the 35V D.C. line supplied from the outdoor unit to the indoor unit.
The circuit consists of three small circuits and one part as below.
Oscillator circuit that generates the approx. 38kHz transmitting signal.
Modulation circuit that composes of an interface signal sent from the micro computer and the f=38kHz transmitting signal.
Demodulation circuit that picks up the interface signal from the communication signal of approx. 38kHz.
Interface transformer that picks up the interface signal from the 35V D.C. line and superimposes.
The timing of the interface
●
The outdoor unit transmits the REQ signal (request signal to indoor) to the indoor unit one, the indoor unit, after transmitting
the REQ signal, transmits the SS signal (the operation order) to the outdoor unit. Then after receiving the order from the
indoor unit one, the outdoor unit transmits the REQ signal to the indoor unit two. Similarly, the indoor unit two receives the
REQ signal and transmits the SS signal.
The micro computer in HIC-A (which is for A cycle) controls the indoor unit one and two, the micro computer in HIC-B (which
●
is for B cycle) controls the indoor unit three and four.
The interface communication between the indoor and outdoor unit in A cycle (one, two) and B cycle (three, four) performs
●
individually. The mutual operation information of A cycle and B cycle is interchanged each other as the inter-micro computer
communication.
The state of the interface communication between the indoor and outdoor unit is under watch. In the case of fault, the self-
●
diagnosis lamp will indicate the state as table -1.
When the interface works normally, measure the voltage (by the indicator style tester with 1V full scale, AC sampling range)
●
between C1D1, C D , C3D3, and C4D4 each terminal. The indicator will swing slightly. If the indicator doesn't swing at all,
it is likely to have some troubles in the outdoor control P.W.B. interface circuit. However, please accept that the check with
the tester is just for a reference value.
Table -1
Self-diagnosis
name
In and outdoor unit communication
error 1 of A cycle
1 blink
No blink
In and outdoor unit communication
error of A cycle
blinks
No blink
In and outdoor unit communication
error 3 of A cycle
3 blinks No blink
In and outdoor unit communication
error 1 of B cycle
No blink
1 blink
In and outdoor unit communication
error of B cycle
blinks
No blink
In and outdoor unit communication
error 3 of B
3 blinks
No blink
Communication error of outdoor
micro computers
No blink 9 blinks
(Caution)
In A cycle and B cycle, the communication error is checked independently.
As the examples shown in Table - , it is possible that only one cycle is normal, or another trouble in the other cycle is also
indicated.
Table -
Indication example of combined
troubles.
A cycle: In/outdoor unit communication error 1, B cycle: Normal operation
1 blink
No light
A cycle: In/outdoor unit communication error ,
B cycle: Stop operating because of peak current cut off
blink
blink
A cycle: In/outdoor unit communication error ,
B cycle: Communication error 1
blink 1 blink
Trouble items
Communication error of indoor unit 1:
Unconnection to indoor unit 1
①
No communication between indoor
Indoor control P.W.B.
unit 1 and outdoor unit
③
Communication error of indoor unit :
Unconnection to indoor unit
①
No communication between indoor
Indoor control P.W.B.
unit and outdoor unit
③
Communication error of indoor unit 1
Unconnection to indoor unit 1 and
①
and : No communication between
Indoor parts
indoor unit 1 [ ] and outdoor ③
Communication error of indoor unit 3:
Unconnection to indoor unit 3
①
No communication between indoor
Outdoor control P.W.B.
③
unit 3 and outdoor unit
Communication_error of indoor unit
①
4: No communication between indoor
②
unit 4 and outdoor unit
Communication error of indoor unit 3
Unconnection to indoor unit 3 and 4
①
and 4, No communication between
Indoor parts troubled
indoor unit 3[4] and outdoor unit ③
No communication between outdoor
Outdoor control P. W. B.
A cycle micro computer and B cycle ①
micro computer.
- 280 -
Main check point
Indoor parts troubled
②
Indoor parts troubled
②
CD reverse connection
②
SW-D-P.W.B. Outdoor control P.W.B.
④ ⑤
Indoor parts troubled
②
Unconnection to indoor unit 4
Indoor electric parts troubled Outdoor control P.W.B.
③
CD reverse connection
②
SW-D-P.W.B. Outdoor control P. W. B.
④ ⑤
Example of
checking
See A
See B
See C
See A
See B
See C