Mitsubishi Electric PUHY-P168, Service Handbook

Page: 323 / 404

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[
IX
Troubleshooting ]
[3] Investigation of Transmission Wave Shape/Noise
1. M-NET transmission
Control is performed by exchanging signals between the outdoor unit and the indoor unit (M-NET remote controller) through
M-NET transmission. Noise interference on the transmission line will interrupt the normal transmission, leading to errone-
ous operation.
(1) Symptoms caused by noise interference on the transmission line
(2) Wave shape check
Check the wave pattern of the transmission line with an oscilloscope. The following conditions must be met.
1) Small wave pattern (noise) must not exist on the transmission signal. Minute noise (approximately 1V) can be gen-
erated by DC-DC converter or the inverter operation; however, such noise is not a problem when the shield of the
transmission line is grounded.
2) The sectional voltage level of transmission signal should be as follows.
Cause Erroneous operation Error code Error code definition
Noise interference on
the transmission line
Signal is transformed and will be misjudged as the
signal of another address. 6600 Address overlaps
Transmission wave pattern is transformed due to
the noise creating a new signal 6602 Transmission pro-
cessor hardware er-
ror
Transmission wave pattern is transformed due to
the noise, and will not be received normally leading
to no acknowledgement (ACK). 6607 No ACK
Transmission cannot be performed due to the fine
noise. 6603 Transmission circuit
bus-busy
Transmission is successful; however, the acknowl-
edgement (ACK) or the response cannot be re-
ceived normally due to the noise. 6607
6608 No ACK
No response
Logic Voltage level of the transmission line
0 V
HL
= 2.0V or higher
1 V
BN
= 1.3V or below
[With transmission]
[Without transmission]
No fine noise allowed
No fine noise
allowed
52 52 52 52 52
V
BN
V
HL
Logic "0" Logic "1"