Samsung SCX-1150F Repair Manual page 51

CIRCUIT DESCRIPTION
3-12 LIU PBA
3-12-1 Background of Line Connection Part
This LIU is designed for the standards (FCC, CTR 21 etc.) of America and Europe where donít allow the Handset, and
the line interface is applied for sending/receiving 33.6k bps. However, contact by 33.6k bps allows just for using FM336
modem of Connexant Co., and provisions is given as below for some countries, require the special function.
- Greater Britain: 3,4,8, (#3, #4: TIP, Ring, #8:Shunt)
- United States and some other countries: 3,4 (TIP, Ring)
United States and some other countries, where apply CTR21 (Common Technical Requirements), are using Modular
Jack #3, #4, and the Modular Jack Harness is designed for joint use of America and Europe counties.
3-12-2 Functions
3-12-2-1 DC Conditions
The normal conducting rage of LIU is 12mA-90mA. Because no more than 60mA current cannot flow in terminal by
applying the CTR21 standard, no more than 60mA DC flows in the Current intercept circuit when the current, which
flows via Bridge Diode (BD1) and Q2, is connected to LINE_A, LINE_B, and LINE_C. It means an entire line current,
flows through LIU, isn't over 60mA.
- CTR21 standard: 12mA-60mA
- United States and other countries standard: 12mA-90mA
The characters of DC are defined as bellows with voltage of the Line input from the Gate input part of Q1 and R20,
which is connected to the Source of Q1.
-VDCR=VLI + ILINEXR20
(VDCR: Tip-Ring DC voltage), ILNE: Line current
VLI: Line Input voltage, VLI=BVD1+VCE (Q2)+VDS (Q1)
In this part, a voltage drop is not considered to Q3 (2SA 1156), R12, R11, etc. at the moment of forming DC loop with
applying CTR21 standard. The DC resistance of terminal is about 70W higher when applying CTR21 standard than
applying America standard.
Not only CML1 (Relay), but also U6 (PC817) must be turned on for forming a DC Loop. The base of Q6 (KSC945)
must be controlled by /DP terminal, and U6 must be turned on to flow the current in Q1,Q2,and R20 via the bridge diode
(BD1) at the same time the CML_1 When the base of the Q4 gets the line voltage from DTR terminal, Q3 is turned on
and flows to Q2 via R11 by applying the CTR21 standard. When the line current is more than 60mA, Q5 is turned on,
but Q3 and Q4 are turned off. The most of current is wasted at R12 (1kW, 2W), so it canít flow more than 60mA. The
1% of tolerance resistance must be use for R11 under the condition of turning on the Q5.
3-12-2-2AC Conditions
AC Impedance of the LIU is basically 600ohm, and it is possible to make it as complex impedance by using C36, R47,
and R48.
- United States: vertical impedance ‡ 600W (±30%)
CTR21: vertical impedance ‡ 270ohm + 750ohm//150nF (more than 1- 4dB)
3-12-2-3 MF Dialing
Repair Manual
3-48
Samsung Electronics