Hitachi RAK-15QEF, Service Manual

Page: 72 / 82

9
9
How to identify sources of jamming in the reception of remote control signals
[ Situation ] The product may become poorly responsive to remote control signals due to external factors even though the
product itself is trouble-free.
[ Estimating sources of jamming ] Identify the installation status of the air-conditioner and the indoor and outdoor
environments to identify possible causes of the jamming.
·
Indoor lighting equipment (quantity, type, location)
·
Remote control units of other electrical products and equipment
·
Is the grounding for the air-conditioner shared with other equipment?
·
Are the surroundings of the air-conditioner clear of wireless antenna?
·
Is the remote control light-receiving unit protected from direct sunlight?
Checking points
·
Turn on and off the lighting equipment and check for its effects on the reception of remote control
ǂ
signals.
·
When cold, the fluorescent lamp tends to emit infrared rays with wavelengths close to those used in
ǂ
remote control.
ǂ
If you cannot detect the phenomenon about which your user is complaining at the time of your visit,
ǂ
such as "the product sometimes fails to receive remote control signals" and "the product fails to
ǂ
ǂ
receive remote control signals in the morning alone", then turn off the lighting for about 20-30 minutes
ǂ
and wait for the fluorescent lamps to cool down before conducting another check.
ǂ
There are even cases where the product fails to receive remote control signals for 1 to 2 minutes only
ǂ
after the lighting equipment is turned on.
·
The noise status may vary with the dimming of the lighting equipment.
ǂ
In the case of lighting equipment with a dimmer, therefore, conduct a
ǂ
check with all the light intensities.
·
If the lighting equipment is the source of the jamming, the remote control
ǂ
light-receiving unit output usually shows a noise waveform as shown in
ǂ
the right-hand figure. In the case of slight jamming, this kind of waveform
ǂ
will not cause practical problems. However, intense degrees of jamming
ǂ
will disable the reception of remote control signals.
·
When the fluorescent lamp is old and is flickering, it may cause disorders
ǂ
in the reception of remote control signals.
Actions proposed
1. Make it hard for light of the lighting equipment to enter the
ǂ
remote control light-receiving unit.
·
Separate the lighting equipment from the indoor unit.
·
Raise the lighting equipment.
·
Cover the upper half of the light-receiving panel from its rear
ǂ
side with aluminum tape or black vinyl tape.
2. Add an interference filter to the front panel of the remote control light-receiving unit.
ǂĆ
Lighting equipment that produces strong jamming exists although rarely.
ǂǂ
Some problems may therefore be unsolvable by managing the air-conditioner side alone.
Effects of lighting
equipment
(fluorescent lamps)
[ Checking and actions ]
This will also affect the reception of remote control signals.
Therefore, set the range to be covered with tape to a range
that is problem-free in practice, while checking the reception status.
Output waveform of the
remote control light-receiving unit
10 ms (or 8 ms) period
Indoor unit
Make it
farther
Lighting
equipment
Make it higher
Checking points
·
If, on the remote control unit of a TV or audio equipment, its sound volume key or
ǂ
something similar is left pressed, infrared signals become continuously sent,
ǂ
thereby jamming the reception of remote control signals.
·
Check how the remote control unit and related components are stored, thereby
ǂ
checking if there is any possibility that a button may be inadvertently left pressed
ǂ
on the remote control unit of other equipment.
Actions proposed
If there is any such possibility, give explanations to your users to that effect and
instruct them to exercise caution.
Effects of the
remote control
units of other
equipment
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