Sony WRR-805A Service Manual page 44

(4) CPU block
The CPU (IC602) block controls the following functions.
LCD display
. Received channel display
. Audio output display
. Battery exhaustion display
. Error message display
Muting control
The audio signal is muted when necessary by
detecting the RSSI signal, the tone signal, the noise
level, and battery tone signal.
LED display
. RF input level display
The RF input level is displayed in three levels by the
LED lit in green, red, or turned off by using the RSSI
signal. (D602).
About the learning mode
In the learning mode, initial setting can be done for
correction of the undesired differences in the RF muting
level and in the RF input display of the LEDs, which are
caused by changes inherent in temperature and between the
receiving channels.
Accordingly, when sensitivity related parts (band-pass
filters, RF devises, etc.) have been replaced, or readjustment
has been carried out to the RF amplifier stages, initial setting
is required (refer to "3-2-3. Muting Level and RF Level
Adjustment").
About EEPROM (IC604)
The EEPROM keeps the set receiving channel in memory.
When the equipment is turned off, and then turned on again,
the last selected channel can be restored.
The EEPROM also keeps in memory the RF input level
corresponding to the receiving channel by the initial setting
of RSSI signal at the learning mode.
If "Error11", that is an indicative of the data error in the
EEPROM, is displayed, initial setting shall be carried out
again in the learning mode.
6-2 WRR-805A (CE, AU)