Samsung SF-4500 Service Manual page 57

6-3 LIU PBA
6-3-1 Summary
LIU(Line Interface Unit) circuit added only to
SF-4500, SF-4500C is controlled by the main circuit.
It monitors telephone line and helps interface
between the system and the telephone line. It uses
1-LIU(STI9510) to control the whole LIU,
MODEM/LINE INTERFACE, RING SIGNAL
DETECTOR, DIALER, LINE CURRENT
DETECTOR, and SERIAL INTERFACE.
6-3-2 Modem/Line Interface
This is the path through which transmitted and
received data of modem is put in and out.
• CML1 Relay: It divides telephone line into
external telephone and fax.
• U3-3 TIT(Transformer Input from Transformer):
This single ended input receives image signals
from modem through transformer T2 and
transmits them on telephone line.
• U3-40 ROT(Receive Output Transformer): This out-
put transformer receives signals on telephone line
and delivers them to modem through
transformer T1. It has AC impedance of 10Kohm or
over.
• AC impedance: Normal operation range of
U3(STI9510) is from 15mA to 100mA. DC
characteristics depend on the voltage of U3-37
LI(Line Input) terminal and the voltage of
resistance R48 between U3-37 LI(Line Input)
terminal and U3-39 LS terminal.
6-3-3 Ring Signal Detector
• U3-28(MO) terminals are ring signal output
terminals. Q4 and Q5 put out ring signals and
drive Piezzo. It has only the functions related to
ring detection such as driving the photocoupler of
U4 and delivering ring signals to MFP
controller of the main.
6-26
6-3-4 Dialer
6-3-4-1. MF DIAL
• Default mode it is set in DP. You can change it to
MF mode by control of MFP controller.
• MF signal can be measured at (tone level of low
group: typical - 14dBm) U3-4 MFO(DTMF
Generator Output). The signal is adjustable by R40,
R41 and C29. The adjusted signal enters U3-9 MFI
(DTMF Amplifier Input) and is amplified to be
transmitted on telephone line.
• U3-39 LS(Line Current Sense Input) terminals
show the final signals transmitted to telephone
line.
6-3-4-2. DP DIAL
• If U3-2(DMS) is made Vcc by R42, it is set at 33:67
DP signal. If it is made Vss by R43, it is set at DP
signal. This product is set at DP signal.
• DP signal is made by U3-27(DPn) terminals. This
signal turns on/off Q1. The signal made at that
time turns on/off Q2, which interrupts DC
current on telephone line and puts out pulse
signal on telephone line.
• U3-35 CS terminals : It makes Make Resistance by
shorting telephone line with Vss during Make peri-
od of DP dial.
6-3-5 Line Current Detector
• When CML1 relay connects telephone line, U3
(STI9510) of LIU board and MFP controller of the
main board (U16) start communication through
UART. U3 of LIU board sends signal that includes
information of line current value, whenever it
receives orders or data from U16 of the main board.
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