Samsung RS20NCSL, Service Manual

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10-6. Key scan and display circuit part
1) Description of key scan and display drive action
As a following each part wave, “ HIGH” output is send out, by use of three terminals of MICOM No #5,6,7 by
6 msec intervals. This signal passes through input terminal of IC05 and is displayed to output terminal. At this
time, the peak to peak voltage of rectangle wave is about 12V, the shape of output wave is like following.
2) KEY SCAN
When GRID #3 wave is output, this signal is supplied to SW1 by passing through panel PCB R5 resistance
10
℃
. At this time, pressing SW1 makes a signal small by R508(6.8
㏀
) and R505(12
㏀
), and impress peak to
peak 4.5V to MICOM. MICOM decides that GRID #3 wave is input and changes the function corresponding
to SW1. Like this, each GRID wave is recognized.