Panasonic KX-TES824LA Service Manual page 181

c) Bell ringing trip section
When the telephone is a signal line telephone, extension calling is executed by means of a ringing signal. When the ringing
signal is supplied, RL201 turns ON and the current flows are as follows:
Bell transformer → ringing signal line → RL201 → telephone → R206 → -15V → Bell transformer
25.5.4. Power Failure Through Call Switching Circuit
25.5.4.1. Circuit Operation
If an AC power failure lasts longer than one second (momentary power failure), the COL is directly connected to the extension.
The COL7 will be connected with EXT117.
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KX-TES824LA / KX-TEM824LA /