Oki OKIOFFICE84 Maintenance Manual page 305

4.3 FN5 circuit diagram
1
Lightning arresters (AR1, 2)
The nominal operating voltage is 500 V.
When connecting the ground of the arrestor to the chassis, tighten ARG on the
PCB with a screw. At this time, the PCB is grounded through the power cable.
The TB1 arrestor ground terminal can also be used to connect to the earth directly.
3
Diode bridge (DB1)
This circuit rectifies the loop current so that the DC circuit characteristics are not
affected by a polarity change over the line.
4
DC circuits (Q3, R540, R541, C13, R9, R209)
These circuits provide DC characteristics according to the line requirements.
5
Impedance matching network (R523, R536, C503, R623, R636, C603)
This circuit matches the impedance between the line and equipment to reduce
reflection of transmitted signals.
It provides impedance (return loss) characteristics to meet the line requirement
using the S5-1 and 5-2.
6 Receiving sensitivity (R537, R539, R637, R639)
The receiving sensitivity at line hunting is determined by R539 or R639 and the MF
tone receiving sensitivity at parallel pickup is determined by R537 or R639.
The receiving sensitivity set using DIP switch S5-3 to S5-6.
7
CML (RL1)
This circuit selectively switches the line between the telephone or facsimile.
8
SR (RL2)
This circuit connects the line with the telephone. During facsimile transmission, it
disconnects the telephone.
9
DP (IC5)
This circuit generates pulse dial signals.
0
MUTE (IC7)
During pulse dialing, this circuit closes to reduce the DC loop resistance.
A PP (RL6)
When it detects MF or CNG tones without seizuring a line, it disconnects NT (5) to
increase the input impedance and also sets the receiving sensitivity.
B
MUTE (RL3)
During pulse dialing, this circuit opens to prevent pulse distortion caused by
capacitor C11. When it detects MF or CNG tones without seizuring a line, it opens
to increase the impedance.
C
Pickup RC (R590, C31)
These circuits insert a high-impedance resistor and capacitor serially to prevent the
line impedance from dropping by the line transformer T1.
D Ring detectors (IC1)
These circuits detect a ring signal arriving to the line. If the input ring signal
exceeds a specific voltage, the circuits output a signal of RI having the same
frequency as the incoming RI.
A3 - 35
UNC/WN5/FN5/DN5
40672201TH Rev. 4