IT-B1
SERVICE MANUAL
Canadian Model
Central & South America Model
Photo: WHITE Type
IT-B1
SECTION 3
DIAGRAMS
3-1. PRINTED WIRING BOARD  HANDSET SECTION 
IT-B1
3-2. SCHEMATIC DIAGRAM  HANDSET SECTION  " Refer to page 7 for IC Block Diagrams.
Note:
" All capacitors are in µF unless otherwise noted. pF: µµF
50 WV or less are not indicated except for electrolytics
and tantalums.
" All resistors are in &! and 1/4 W or less unless otherwise
specified.
" % : indicates tolerance.
" ó
: internal component.
" C : panel designation.
" U : B+ Line.
" Connect J2 and J3 with handset cord.
Power voltage is dc 12V and fed with regulated dc power
supply from J3 with 100 &! in series.
" Voltage is dc with respect to ground under no-signal
condition.
no mark : OFF HOOK
( ) : ON HOOK
" Voltages are taken with a VOM (Input impedance 10 M&!).
Voltage variations may be noted due to normal produc-
tion tolerances.
" Signal path.
N : RX (from TEL LINE)
O : TX (to TEL LINE)
P : bell
" Abbreviation
MX : Mexican model
LA : Latin American model
55
IT-B1
3-3. PRINTED WIRING BOARD  CRADLE SECTION  3-4. SCHEMATIC DIAGRAM  CRADLE SECTION 
JW
" IC Block Diagrams
IC2 TEA1112AT
VCC GAR QR VEE MIC+ MIC- AGC IR
16 15 14 13 12 11 10 9
AGC
CIRCUIT
CURRENT
REFERENCE
LOW
VOLTAGE
CIRCUIT
MICRO
MUTE
LED
DRIVER
ATT
1 2 3 4 5 6 7 8
LN SLPE LED REG GAS MMUTE OTMF MUTE
IC3 HM91510AP
R4 R3 R2 R1 MODE TONE PO HKS VDD
18 17 16 15 14 13 12 11 10
VDD
D/A PULSE
CONVERTER GENERATOR
INPUT
INTERFACE
CIRCUIT
ROW/COLUMN DECODER
ROW
PROGRAMMING &
INTERFACE CIRCUIT
COUNTER DATA LATCH
LNB
MEMORY
KERNEL CONTROL CIRCUIT
MEMORY
COLUMN
VDD
INTERFACE CIRCUIT
DIVIDER
OUTPUT
INTERFACE
CIRCUIT
OSC
VSS
1 2 3 4 5 6 7 8 9
C1 C2 C3 C4 KT OSCI OSCO XMUTE VSS