Oki OKIFAX 5400 Maintenance Manual page 340

3-4 TEL-W2D circuit diagram
TEL-W2D board is for the Germany version only.
1) Speech IC
General functions of the speech IC are as follows:
• Basic speech functions included.
• Separate receive pre-amplifier with signal output terminal
• Separate receive power amplifier input terminal, cause it is possible to mixing input.
• Balanced input for microphone input to provide immunity to common mode noise.
• MF pre-amplifier input terminal is possible to mixing input.
• Dial pulse waveform improvement circuit included.
• Manual pad function included.
• The transmit, receive, and DTMF amplifiers are provided with AGC in accodance
2) Sending Level Adjustment
The sending level can be adjusted by resistor R55 connected in parallel with the section
in front of the transmitter. Increase the resistor value to lower the sending level, and
decrease the value to raise the level.
3) Receiving Level Adjustment
The receiving level is determined by the resistor value of R35. Decrease the resistor
value of R35 to lower the receiving level, and increase it to raise the level.
4) Frequency Response Adjustment
The high range frequency response of the transmitter is determined by the capacitance
of C61. Increase the capacitance of C61 to lower the high range level, and decrease
the capacitance to raise the high range level. The low range frequency response is
determined by the capacitance of C36 and C37. Increase the capacitance of those
capacitors to raise the low range level, and decrease the capacitance to lower the level.
When the capacitance of C36 and C37 are changed, both capacitors should have the
same value.
The high range frequency response of the receiver is determined by the capacitance
of C29. Increase the capacitance of C29 to lower the high range level, and lower the
capacitance to raise the level. The low-range frequency response is determined by the
capacitance of C26. Increase the capacitance to raise the low-range level, and lower
the capacitance to decrease the low-range level.
5) Side-Tone Adjustment
The side-tone level is determined by the values of R19, R22 and C16.
Note: Changing the side tone level setting affects the sending and receiving levels, the
6) DC V-I (voltage-versus-current) Characteristics Adjustment
The DC V-I characteristics can be changed by mounting or not mounting D10 and D11.
When D10 and D11 are mounted the DC V/I value is raised. When these diodes are
deleted the DC V/I value is lowered. R202 is a 0 W resistor, which is mounted when
D10 and D11 are not being installed.
40838301TH Rev.1
with the line circuit.
verification and readjustment of the sending and receiving levels, and the
verification and the readjustment of the side tone level are required.
TELU/TEL-W2/TEL-W1/TEL-W2D/TEL-W2F
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