Panasonic KX-F900 Service Manual page 156

7-5. AUTO DISCONNECT CIRCUIT
(1)Function:
This circuit is used to detect the fact that another telephone connected to the same line is OFF-Hook while the unit is in the
time of TEL/FAX's arrival bell ringing operation.
(2)Circuit Operation:
Tip (Ring)---*D101 ---,Q101 -* C107 -* D102 -* Rl14 -* Q102 --* PC103.
Duringthisinterval C107 chargesand the base of Q102 becomeshigh,and PC103 pin(2)becomeslow,causingPC103 to
go ON. If a parallel-connected t elephoneor externaltelephoneis put intoan OFF-HOOK status,,chargeceases to flow
Cl 07 and the base ofQ102 becomeslow,causingPC103 to go OFF.
When a line isconnected,Q102 and PC103 go ON, causingpin5 of IC151 to go low.When the line isdisconnected, Q 102
and PC103 go off,causingpin 5 of IC151 to go high.
7-6. TAM INTERFACE CIRCUIT
This circuit is for to switch between FAX receiving and external TAM's message recording automatically.
This circuit consists of EXT. TAM OFF-HOOK detect circuit, Monitor Transformer, Multiplexer, Amplifier, VOX detect circuit.
In details please refer to page 142. TAM INTERFACE SECTION.
7-7. LINE AMPLIFIER AND SIDE TONE CIRCUITS
(1)Circuit Operation
The reception signal received as outputfrom the line transformer T 101 is given as inputto R202, C205 to IC201 pin (6), ant
it is inputtedtothe receptionsystemat an amplifiergain10.1 dB from pin7.
The transmission signalgivenas input to IC201 pin (2) via R210, C203 is amplifiedto about15 dB, It is outputted form pin 1
of IC201 and itistransmittted to T101 via R201, C202,T101.Withoutside tonecircuit,thetransmission signalhere wouldreturr
completely to thereceptionamplifiervia R201, C202. Here,the signaloutputfrom IC201 pin (1) passesthrough C218, R203
R204, C207 and entersthe amplifierIC201 pin (5), and thisis usedto cancelthe returnpart of the transmission signal.
This is the side tonecircuit.
Transmission Signal: C203 --* R210 --* IC201 (2-1) _ C202 --, R201 .L, T101 ---*TEL LINE
C218
R203
R204
C207
Reception Signal: TEL LINE--, T101 _ R202---, IC201(5,6-7) _ C210
(Side Tone)
156-