Service manual

Circuit Description
3-36
3-7 LIU PBA
3-7-1. SUMMARY
LIU WIRE CONNECTS Main B’D’s MODEM AND LINE PARTS, AND IMPEDANCE MATCHING (AC, DC),
RING DETECTION PART and LINE SEIZURE (DIALER).
3-7-2. DC MATCHING PART
Normal movement range of LIU is 12mA ~ 9mA.
Adapting CTR21 standard, the regulation limits to 60mA CURRENT flow through the terminal.
Therefore, select (*:for EU PIT) Option to connect necessary items then the current through LIU will not
exceed 60mA.
• CTR21 Standard(Europe) : 12mA~60mA • OTHER Standard (U.S.) : 12mA~90mA
DC has a character to pass through the LINE. And with Q1 (VN2410) GATE section’s LINE INPUT corrent
and Q1 Source connection to R20, can be decided as follows :
• -VDCR = VL1 + ILINE X R20
(VDCR : Tip-Ring CD Voltage, ILINE :
Current flow)VL1:Line Input Voltage, VL1=VBD1+VCE(Q2)+VDS(Q1)
3-7-3. AC MATCHING PART
Basic LIU’s AC IMPEDANCE is 600 and uses R47. 48. C36 to possibly control combined IMPEDANCE.
• U.S. Usage : A terminal IMPEDANCE Æ 600W(±30%)
• CTR21 : A Terminal IMPEDANCE Æ 270+750W//150nF
3-7-4. DIALER PART
*MF DIAL
DTMF Dialing is controlled by MODEM and should be selected by appropriate LEVEL and On-off Time output
based on each countries’ own National specification.
• Freq. Tolerance : ±1.5%
High Group : 1209, 1336, 1477, 1633Hz
Low Group : 697, 770, 852, 941 Hz
*DP DIAL
Controls from MAIN through / DP-Terminal.
for U.S.Usage, set time to DF signal of 40:60 M/B. DP signal is made of U6 (pcb817). The DC current which
flows thru Q2 Base is regulated by On/Off switch and turns to DP dial signal with a COUPLER.
• CTR 21 does not have telephone capability but has the number 3 and 4 Line Connection. No DP condition
but possibility to get approval only on DTMF Dial based terminal.
3-7-5. RING DETECTION PART
RING SIGNALS from the LINE section (TIP, RING)are further passed through C5, R3, ZD1, and ZD2 and
ends up at U9, (PC 814). U9 then detects above RING SIGNAL and passes the output to MAIN B’D. The wilre
diagram’s C5 is RINGER CAPACITOR and it normally uses 1UF/250V.
A R3 limits AC current and controls upper and lower REN meter.
U.S. Usage CTR21
High Freq Level -9.0+2.0/-2.5 -7.0 +1.0/-2.0
Low Freq Level -9.0+1.0/-2.0 -11.0+2.5/-2.0