Panasonic KX-TC1801B Service Manual ▷ View online
11 NEW CIRCUIT OPERATION (Base Unit)
11.1. Power Supply Circuit
As indicated in the illustration, the various voltages are supplied constantly to their respective blocks. A time constant is used to
compensate for momentary dropouts in the AC power supply.
compensate for momentary dropouts in the AC power supply.
11.2. Charge Circuit
The voltage from the AC is supplied to the main charge circuits. Ultra charge (150 mA on the average) of maximum 6 hours is
started soon after the Handset is placed on the base unit. Then it changes to normal charge (90 mA on the average) of 5 hours.
Finally the mode changes to trickle charge (45 mA) to prevent overcharging.
started soon after the Handset is placed on the base unit. Then it changes to normal charge (90 mA on the average) of 5 hours.
Finally the mode changes to trickle charge (45 mA) to prevent overcharging.
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11.3. Bell Detector Circuit
When the DSP detects the Bell signal, pin 67 of IC501 repeats High/Low and then C-ID LED (LED542) is flashed.
At this time, if the Handset has been charged or not, the data from IC501pin 25 is sent through RF Unit and then the Handset´s
ringer rings.
ringer rings.
11.4. Line Interface
In talk status, the RLY output from pin 99 of IC501 changes to High level, it causes Q122 and Q121 to turn on. A telephone line
is seized in result. The loop current flows from D101(+)
is seized in result. The loop current flows from D101(+)
→
Q121, in that order. A pulse signal that repeats switching between high
and low level is output from pin 99 of the IC501. This switches the line loop on and off to generate the dial pulse signal.
11.5. DTMF Signal
When the DTMF data from the Handset is received, the DTMF signal is output from pin 36 of the IC501 and sent to the line through
R431
R431
→
C432
→
C433
→
Q131.
11.6. Line Sending Signal
The ADPCM signal input from the RF unit is decoded by IC501 (DSP), and the voice signal output from IC501-36 is amplified at
Q131 to be output to the line circuit.
Q131 to be output to the line circuit.
11.7. Line Receiving Signal
The voice signal from Q131 is amplified at Q461, then led to pin 38 of IC501 (DSP). IC501 encode the input voice signal to output
to RF unit.
to RF unit.
11.8. Power Down Detection Circuit
The power down detection circuit (IC331) outputs the interrupt signal of active LOW to pin 57 of IC501 (DSP) when the power
supply voltage becomes lower. Receiving the interrupt signal, IC501 quites the system when the power is down.
supply voltage becomes lower. Receiving the interrupt signal, IC501 quites the system when the power is down.
11.9. ID Code Setting
When the Handset is placed on the base unit, new ID data is sent to the Handset through RF Unit.
After the ID code setting is success, the Handset rings “Pip“
After the ID code setting is success, the Handset rings “Pip“
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11.10. Parallel Connection Detection Circuit
Function:
In order to disable call waiting and stutter tone functions when using telephones connected in parallel, it is necessary to have a
circuit that judges whether a telephone connected in parallel is in use or not. This circuit determines whether the telephone
connected in parallel is on hook or off hook by detecting changes in the T/R voltage.
In order to disable call waiting and stutter tone functions when using telephones connected in parallel, it is necessary to have a
circuit that judges whether a telephone connected in parallel is in use or not. This circuit determines whether the telephone
connected in parallel is on hook or off hook by detecting changes in the T/R voltage.
Circuit Operation:
Parallel connection detection when on hook:
When on hook Q115 is ON, the voltage is monitored pin 40 of IC501. There is no parallel connection if the voltage is 1.65 V or
higher, while a parallel connection is deemed to exist if the voltage is lower.
Parallel connection detection when on hook:
When on hook Q115 is ON, the voltage is monitored pin 40 of IC501. There is no parallel connection if the voltage is 1.65 V or
higher, while a parallel connection is deemed to exist if the voltage is lower.
Parallel connection detection when off hook:
When off hook Q115 is OFF, the voltage is monitored pin 40 of IC501; the presence/absence of a parallel connection is determined
when the voltage changes by 0.2 V or more.
When off hook Q115 is OFF, the voltage is monitored pin 40 of IC501; the presence/absence of a parallel connection is determined
when the voltage changes by 0.2 V or more.
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KX-TC1801B
12 BLOCK DIAGRAM (Handset)
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KX-TC1801B
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