Panasonic KX-TCD951EB / KX-TCD955EC Service Manual ▷ View online
33
KX-TCD951EB/KX-TCD955EC
1.8 CLOCK GENERATION (SEE Fig. 28)
A single clock generator in the BBIC uses an external crystal X1 to derive all clock frequencies used in the handset.
The crystal is tuned to the exact frequency of 10.368 MHz during manufacture by feeding a DC voltage from an
internal DAC (from pin 12) to the varicap diode D12 (TP25). The R F C L K output (pin 10, TP56) is a buffered clock
signal at 10.368 MHz for the Frequency Synthesizer, that is only active during the PLL lock period (see section 1.3).
The basic data rate for TX-DATA and RX-DATA is 1.152 Mbits/s, which is divided by 9. The data rate for the serial
interface to the phase-lock-loop is also 1.152 Mbits/s.
1.9 KEYBOARD (SEE Fig. 29)
The keyboard “On” button is connected directly to pin 41 of the BBIC (TP10). When pressed it turns the handset on
and off (must be held for off
)
.
All other keys are connected in a row/column matrix. They are scanned in six rows using
scan pulses (only active when keys are pressed) from IC1 pins 28 to 33. The four key matrix columns are input to the
BBIC on pins 31 to 34.
Fig. 29
Circuit Diagram
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KX-TCD951EB/KX-TCD955EC
1.10 FA C TO RY SERIAL PORT (SEE Fig. 26)
In order to communicate with the handset during manufacture and servicing (using a PC) a serial data link has been
provided. Serial data input/output is provided on J6 (TP65), and a ground is provided on J7. The bi-directional serial
data line is split into two at IC1 pin 27 (input) and pin 26 (output). Data rate is 9600 baud or 115.2 kBaud.
D13 provides ESD protection, and R37 and C56 provide RF de-coupling.
1.11 BUZZER CIRCUIT (SEE Fig. 30)
A square-wave signal from IC1 pin 45 is used to sound the buzzer via switching transistor T5 (TP22). Various tones
and cadances are used dependent on function. Buzzer volume is varied by changing the duty cycle of the drive
waveform. D11 provides quenching of back-emf generated when T5 turns off
.
1.12 BATTERY SUPPLY (SEE Fig. 30)
The three cell NiCd/NiMH rechargeable battery supplies the handset via 2A fuse (actually a coil), and is de-coupled by
C3 and C4. It directly supplies T3 in the baseband section, and also the Tx PA in the RF Section. It also supplies IC1
(de-coupled by C9), and most of the RF Section (VCC-OC) (decoupled by R35 and C47, C48 and VCC-PA )
.
1.13 MAIN 3V REGULATOR (SEE Fig. 30)
The BBIC measures the battery voltage on pins 58 using an internal ADC. If the battery voltage is below 3.36 V,
TC3 is
switched to power off mode. R7 and C5 provide a reset pulse (TP84) used for resetting the BBIC when power on.
The +3 V supply (TP10) is fed to the BBIC, Flash PROM, EEPROM, and Display Driver.
1.14 BATTERY CHARGING CIRCUIT (SEE Fig. 30)
The charge circuit is designed to operate with a constant current charger in the base. L1, L2 and D2, D4 protect
against electro-static discharge (ESD). The charging current from the base is turned on and off by T1 using a control
signal from the BBIC (pin 39, TP6) via T2. R3 provides initial current in the event of a totally flat battery, and D6 pro-
tects against the high voltage present on the charge contacts if there is no battery in the handset. R4 and R5 provide a
signal for the BBIC to detect (pin 40) that the handset had been placed on the base charger. If
the handset is off, it will be switched on, and charging will start. D2, D3, D4 and D5 act as
steering diodes to enable the handsdt to be placed on the cradle either way up (i.e.the handset is
reversible).
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KX-TCD951EB/KX-TCD955EC
Fig. 30
Circuit Diagram
BUZZER
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KX-TCD951EB/KX-TCD955EC
ADJUSTMENT (BASE UNIT)
Adjustment objectives
Tools required for adjustments
Frequency counter
Personal computer
Serial communication tool
Test software (batch files)
Line simulator
Oscillator
Audio level meter
Item(1)
1. Connect the serial link to test computer to J102 (serial data) and J103 (GND).
2. Connect the AC adaptor.
3. Connect the frequency counter to TP148 (SCLK) and J103 (GND).
4. Send batch file “FIXFREQ.BAT”.
5. Send “SETFREQ.BAT” to set the clock frequency.
The default value is 80. Increase
the value to increase the frequency.
The clock frequency must be
3,456 kHz ± 0.007 kHz.
Adjustment item
Symptom
Synchronization with the portable handset is lost
immediately.
No link is established.
Remedy
Perform the adjustments described in item(1).
Clock frequency
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