Panasonic KX-TC1868B / KX-TC1871B / KX-TC1872B Service Manual ▷ View online
12 BLOCK DIAGRAM (Base Unit)
KX
-T
C186
8B
/
K
X
-T
C
1871B
/
K
X
-T
C
187
2B
45
13 NEW CIRCUIT OPERATION (Base Unit)
13.1. SP-PHONE RX Circuit
Circuit Operation:
Telephone Line (T/R)
Telephone Line (T/R)
→
Q131
→
C463
→
R448
→
C442
→
R464
→
C441
→
pin 38 of IC501
→
pins 32 and 33 of IC501
→
Speaker
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KX-TC1868B / KX-TC1871B / KX-TC1872B
13.2. SP-PHONE TX Circuit
Circuit Operation:
MIC
MIC
→
C724
→
C725
→
C726
→
R726
→
pin 47 of IC501
→
pin 36 of IC501
→
R431
→
C432
→
C433
→
Telephone Line
13.3. Auto Disconnect Circuit
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 a receiving
status or OGM transmitting status.
This circuit is used to detect the fact that another telephone connected to the same line is OFF-HOOK while the unit is in a receiving
status or OGM transmitting status.
Circuit Operation:
The voltage pin 40 of IC501 is monitored. If a parallel-connected telephone is put into an OFF HOOK status, the presence/absence
of a parallel connection is determined when the voltage changes by 0.2V or more.
When the set detects tha parallel-connected telephone is OFF HOOK status, the line is disconnected.
The voltage pin 40 of IC501 is monitored. If a parallel-connected telephone is put into an OFF HOOK status, the presence/absence
of a parallel connection is determined when the voltage changes by 0.2V or more.
When the set detects tha parallel-connected telephone is OFF HOOK status, the line is disconnected.
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KX-TC1868B / KX-TC1871B / KX-TC1872B
13.4. Power Supply Circuit
Function:
Power from the AC adaptor passes through a regulating block consisting of IC301.
Power from the AC adaptor passes through a regulating block consisting of IC301.
Circuit Operation:
IC401 is a regulated power supply. The voltage at point A is regulated to 4.5 V by IC301.
The voltage at point B is dropped by D306 and D307 to 4.1 V.
The voltage at point C is dropped by D511 to 3.8 V.
IC401 is a regulated power supply. The voltage at point A is regulated to 4.5 V by IC301.
The voltage at point B is dropped by D306 and D307 to 4.1 V.
The voltage at point C is dropped by D511 to 3.8 V.
The voltage at point D is dropped by Q304 to 4.3V
The voltage at point E is dropped by Q312, Q601 to 4.1V
13.5. DTMF Signal
When the DTMF data from the Handset is received, the DTMF signal is output from pin 36 of IC501 and sent to the line through
Q131.
Q131.
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KX-TC1868B / KX-TC1871B / KX-TC1872B
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