DOWNLOAD Panasonic KX-MB283RU / KX-MB783RU Service Manual ↓ Size: 15.15 MB | Pages: 127 in PDF or view online for FREE

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1. Function

This unit has a lithium battery (BAT300) which works for the Real Time Clock IC (RTC: inside IC300).
The RTC continues to work, backed up by a lithium battery even when the power switch is OFF.

2. RTC Inside (IC300) Backup Circuit Operation

When the power switch is turned ON, power is supplied to the RTC (inside IC300). At this time, the voltage at pin AD4 of the
IC300 is +3.3V. When the power switch is turned OFF, the BAT300 supplies power to RTC through DA300. 
When the power switch is OFF and the voltage of +3.3V decreases, pin AD4 of RTC (IC300) becomes roughly the same volt-
age as the battery voltage. RTC goes into the backup mode, in which the power consumption is lower.

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The modem (Included IC300) has all the hardware satisfying the CCITT standards mentioned previously.
ALL processing is controlled by the SOC (IC300) according to CCITT procedures.
This modem (Included IC300) has an automatic application equalizer. With training signal 1 or 2 at the time of G3 reception, it can
automatically establish the optimum equalizer.  

The digital image data sent on ATXD line from modem (Included IC300) .
DAA IC100(6

→9,10), Line side DAA IC101 and the NCU section to the telephone line.

The analog image data which is received from the telephone line passes through the NCU section and enters line side DAA*

IC100. The signals are changed to digital data in IC101 (5,6) ,IC100(9,10

→5) and IC300. In this case, the image signals from

the telephone line are transmitted serially. Here, the internal equalizer circuit reduces the image signals to a long-distance
receiving level. This is designed to correct the characteristics of the frequency band centered around 3 kHz and maintain a con-
stant receiving sensitivity.

The path is the same as Facsimile Reception.

This is the call signal which is generated the SOC (IC300) and sent to the speaker.

 DAA : Direct Access Arrangement

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Composed of ITS circuit and NCU circuit.

The analog section works as an interface between the telephone line.
DAA control ITS circuit and NCU circuit. 
DAA control signals are output from Soc IC300.

[NCU]: Network Control Unit the NCU comprises of the following; DC loop forming circuit to connect with the telephone line;
Switching circuit for other interconnected telephones; Bell detection circuit; Remote fax activation circuit.
Refer to NCU SECTION (KX-MB783RU ONLY) (P.28) for the details.

RING

ARXD

ATXD

BTXD

BRXD

IC200

IC100

IC101

EXTRLY

T

R

T

R

SP(+)

SP(-)

HS_MIC(+)

HS_MIC(+)

HS_SP(+)
HS_SP(-)

AGC

16

5

6

5

6

10

9

8

9

15

1

16

14

12

1

3

13

4

5

10

16

KX-MB783RU: MAIN BOARD BLOCK DIAGRAM

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This section is the interface between the telephone line and external telephone. It is composed of an EXT. TEL line relay (RLY100),
bell detection circuit, TAM interface circuit and line amplifier.

1. Circuit Operation

Normally, this relay switches to the external telephone side and switches to the open side while OFF-HOOK.
IC300 (U25) High Level

→Q100 ON→RY100 (ON)

1. Circuit Operation

The signal waveform is indicated below. The bell signal input  to  IC101 and ring detected signal output from pin 16 of IC100.
IC300 monitor this signal and judged as bell.
TEL LINE

→IC101 (8,9 - 5,6)→IC100 (9,10 - 16)→IC300(L23)

1. Function

This unit is compatible with the Caller ID service offered by your local telephone company. To use this feature, you must sub-
scribe to a Caller ID service. The data for the caller ID from the telephone exchange is sent during the interval between the
first and second rings of the bell signal. The data from the telephone exchange is a modem signal which is modulated in an
FSK (Frequency Shift Keying) format. Data “0” is a 1200 Hz sine wave, and data 1 a 2200 Hz sine wave.
There are two type of the message format which can be received: i.e.the single data message format and multiple data mes-
sage format.
The multiple data format allows to transmit the name and data code information in addition to the time and telephone number
data.
When there is multiple data in the unit, the name or telephone number are displayed.

2. Circuit Operation

The caller ID signal input from TEL LINE is processed with Soc (IC300).
TEL LINE

→IC101 (8,9 - 5,6)→IC100 (9,10 - 5)→IC300(AD26)

1. Function

Another telephone connected to same line activates the unit to the FAX mode by using a DTMF signal.

2. Signal Path

TEL LINE

→IC101 (8,9 - 5,6)→IC100 (9,10 - 5)→IC300(AD26)

This circuit is to switch between FAX receiving and the external TAM’s message recording automatically. 
For details, please refer to TAM INTERFACE SECTION (P.29).