OKIFAX 610, Service Handbook, Page: 139 / 147

8.5 TEL BOARD CIRCUIT DIAGRAM
8.5.1 Ringing Mode:
Ring signal path:
J1
à
LP2
à
JP9( or K5 )
à
L1
à
JP1( or CF1//LF1 )
à
K2
à
C6
à
ZD9,ZD10
à
R2
à
DB1
à
J5(pin12)
à
J5(pin13)
à
C21//ZD7(piezo ringer supply)
à
C34//ZD8(VDD).
Another path exists from C6 and R39 to FCI//C24//R41 for the frequency detector input. R39 is not
only for current limited function but also effect the specification of ring tap function. Ringing circuit
will be connected to await ringing signal when HK is on hook condition.
Operation:
The ring signal is checked at pin FCI (21) for a valid ringing frequency. As soon as a signal is
applied to the line the internal “ring frequency detector” will start provided that the signal level at
FCI is above the trigger threshold (about 2/3 VDD). If the frequency is within the specified range
the melody generator will send a bitstream out of MO (8) charging the piezo ringer via D12 and an
internal high voltage transistor. As soon as a nonvalid or missing ring signal is detected the
bitstream is stopped and the circuit returns to standby.
8.5.2 Dialing Mode:
Dialing circuit:
IC1 R25~30 R50~54 HS/DP (pin10) MODE (pin12) MFL (pin2) and Y1 C31 Q1-5 D13 D14.
Operation:
Y1 C31 constitute a oscillator circuit which will provide to IC1 for dialing element.
IC1-pin12 (MODE) is the switch of T/P. The switch T/P decides the function of DTMF/PULSE. The
function list
l
Pin12 (MODE) connect to pin19 (R54) by T/P switch , IC1 will work on pulse dial (LD 10pps,
40/60 ms).
l Pin12 (MODE) connect to pin20 (R53,D14) by T/P switch , IC1 will work on
l pulse dial (LD 10pps , 33/66 ms , TEMP. MF with tone on first key entry).
l Pin12 (MODE) connect to pin18(R52,D13) by T/P switch , IC1 will work on MF dial (MF only ,
82/160 ms).
Tone dialing:
During TONE dialing the same line conditions as in speech mode apply, except that speech is
muted in both directions and a confidence tone is send to the RX amplifier.
The TONE signal is modulated to the line by controlling the shunt transistor, Q7 during inter-digit
pauses speech is also muted. TONE level is adjusted by a DC voltage at the pin2 (MFL) input.
Pulse dialing:
With pulse dialing, the line has to be interrupted during “Break” periods and short circuited during
“Make” periods. For example “LD 60/40 10pps” mean Break/Make ratio is 60:40 with 10 pulse per
second = the dialing pulse is a 60ms break (line interrupt) followed by a 40ms make (line short circuit).
Dialing number “1” will result in one dialing pulse, total time = 100ms
Dialing number “0” will result in 10 dialing pulse, total time = 10*100ms = 1sec.
Line break pulse are performed by Q1 Q2 being switched off the on-off control signal is output
from the pin10 (HS/DP) switch Q4 (and in turn Q1 Q2) on and off.
Make pulse are performed by Q7 with Q1 Q2 being switched on. The base of Q7 ( = pin25, CS ) is
pulled to VSS , resulting in VLI = VBE
≈
0.7V.
CS is pulled low during the complete dialing period of one digit , which means in worst case
(dialing number “0” ) the circuit cannot be supplied from line and must be buffered by the VDD-
cap, C34. Therefore C34 must be big enough to supply the active circuit for 1 second.