Panasonic KX-F900 Service Manual page 160

9-2, CIRCUIT OPERATION
TAM INTERFACE circuit consists of EXT. [AM HOOK detection circuit, CNG signal from the party's detection circuit, VOX
detection circuit (to judge sound/no-sound) and RL101 (to separate EXT. TAM).
(1) EXT. TAM HOOK detection circuit
The bell comes to EXT. TAM and EXT. TAM seizes the line, causing to make DC LOOP. PC105 detects this voltage. During
detection PC105 (4) becomes low.
(DC LOOP)
Tip ---* POS101 --* L105 --* RL101 (7 -_ 6)3_---* VAR1------]--* L104 --* Tip1 --, (EXT.TAM) _ Ring 1 --* L103 -* R103 --*
L-, R192 -* PC105 J
L105 -*Ring
(2) CNG signal detection circuit
CNG signal from the party's FAX is detected in MODEM IC11 (digital board).
(Signal path)
TEL LINE -* O104 --* T102 --* O176 --* R176 -* IC151 (61)(67) --, R217 --* C214 -* IC202 (10)(11) --, C217 ---* CN271 (9) -*
CN1 (9) --, R97 --, IC10 (2) (1) --* C82 --* R95 --* ICll (45)
(3) VOX
VOX circuit detects if there is a signal or voice in the line. That's why VOX circuit reacts to OGM of EXT.TAM and ICM from
the party.
(Signal path)
TEL LINE -* C104 _ T102 _ C176 --, R176 -* IC151 (61-70) -* C291 ---,D290 --, R296 --* IC101 (6)(7) --, R290
/
--* IC151 (30)
EXT.TEL Line --* VAR1
(4) RL101
Normally this relay switches to the external telephone side (break) and it switches to the open side (make) when the set
changes to facsimile communication from EXT.TAM operation.
IC151 (32) High Level --* Q271 --* ON ---, RL101 (make)
IC151 (32) Low Level --* Q271 --* OFF --, RL101 (break)
(5) Remote receiving
This is the DTMF signal of parallel connection TEL or EXT.TEL between T and R. When the party is FAX, this turns unit to
FAX receiving.
(Signal Path)
To defect DTMF signal in MODEM.
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