Board Descriptions A - 58 OF 5300/5600 Serv Man, P/N 59278301A3.8 TELU Circuit Diagram (option)The TELU board is the control board of the telephone set when the optional telephone assem-bly is installed on the facsimile transceiver.1. Block diagram• Figure A3.8.1 shows a block diagram of TELU circuit.2. General functions of this circuit are as follows:• Speech IC• Sending Level Adjustment• Receiving Level Adjustment• Sending Frequency Response Adjustment• Side Tone Adjustment• DC V-1 Characteristics Adjustment• Return Loss Adjustment• AGC (automatic gain control)• Manual Pad• Sending Frequency Response Adjustment• Receiving Frequency Response Adjustment• Handset Interface3. Explanation of TEL circuit diagramThis section describes functional blocks of individual TEL circuit diagram.3-1 TELU circuit diagramTELU circuit diagram is formed by Speech IC and interface of UNC, HOOK SW andHANDSET.1) Speech ICThe hybrid circuit is formed by Speech IC.2) Handset Interface• Transmitter signal routeSignal from the microphone of the handset is input to pin 15 and 16 of SpeechIC. This signal is determined by the amplification factor and output to thetelephone line via UNC, Hook switch and DB2 (rectifier).• Receive signal routeReceive signal from the telephone line enters Speech IC via UNC, Hook switchand DB2 and is output to pin 2 & 3 of the speaker of the handset.
