No incoming voice heard during telephone conversation!

Make sure that it is set for voice /fax unless you want it set for fax only or voice only, recheck your setting.

Can you still send fax? if sending and receiving are not working you can try to update or uninstall/reinstall the software for this unit..

Hope that helps.............

For more details on how to setup your Lexmark X4650 printer for faxing, please refer to the User's Guide found on the Lexmark website.
Additional info:If you have an answering on the same line as your fax:

To make sure the printer picks up incoming faxes, set Auto Answer to On, and then set the printer to pick up after a greater number of rings than the answering machine. For example, if the answering machine picks up calls after four rings, then set the printer to pick up after six rings. This way, the answering machine picks up calls first and your voice calls are received. If the call is a fax, then the printer detects the fax signal on the line and takes over the call.

If you have a voicemail feature associated in the same line as your fax:

Voice mail and fax can share the same telephone line if you subscribe to a distinctive ring service offered by your telephone company. This feature allows you to have multiple telephone numbers on one telephone line. Each telephone number has a designated ring pattern (single ring, double ring, triple ring, or double and triple ring). The different ring patterns let you know which telephone number was dialed, and which device you should use to answer the call.

If you do not have distinctive ring service, then set the printer to receive faxes manually (Auto Answer Off). This setting lets you receive both voice calls and fax calls, but works best if you use voice mail more often. You need to turn off voice mail whenever you are expecting a fax.

If you have an answering machine connected to the same line as your fax:

To make sure the printer picks up incoming faxes, set Auto Answer to On, and then set the printer to pick up after a greater number of rings than the answering machine. For example, if the answering machine picks up calls after four rings, then set the printer to pick up after six rings. This way, the answering machine picks up calls first and your voice calls are received. If the call is a fax, then the printer detects the fax signal on the line and takes over the call.

If you have a voicemail feature associated to the same line as your fax:

Voice mail and fax can share the same telephone line if you subscribe to a distinctive ring service offered by your telephone company. This feature allows you to have multiple telephone numbers on one telephone line. Each telephone number has a designated ring pattern (single ring, double ring, triple ring, or double and triple ring). The different ring patterns let you know which telephone number was dialed, and which device you should use to answer the call.

If you do not have distinctive ring service, then set the printer to receive faxes manually (Auto Answer Off). This setting lets you receive both voice calls and fax calls, but works best if you use voice mail more often. You need to turn off voice mail whenever you are expecting a fax.

I hope this helps.

Should you need further assistance, please contact Lexmark Technical Support Center.

Step by step information at the link below.
Brother Fax T96
The F/T Mode is used to allow the fax machine and the telephones to share the same telephone line. When a call comes in, the fax machine and all extension telephones on that line will ring according to the number of rings you have set for the Ring Delay.
When the Ring Delay is completed, the fax machine will answer the call and determine if it is a fax call or a telephone (voice) call.
The fax machine can determine this by the signal it is receiving on the telephone line. If someone is sending a fax automatically , the sending fax machine will transmit a fax tone (a series of beeps every 3 seconds).
If your fax machine hears these tones, it will receive the fax.

If the fax machine does not hear any fax tones, it assumes it is a telephone (voice) call and will begin ringing the F/T ring tones (double ring) for the length of time you selected for the F/T Ring Time. These tones will only ring on the fax machine's handset (extension or external phones will not ring). At the end of the F/T ring time the fax machine will go into the receive mode in order to receive a manual fax.
(If the call was a voice call and was not answered, the caller will hear the fax receive tones also).

• If you answer the call before the fax machine(during the ring delay period) and determine it is a fax, you can transfer the fax to the fax machine for receiving.
  
  
• If you answer the call on an "extension" phone and hear a beep every 3 seconds (automatic fax) or silence (manual fax), press *51 or *91 for New Zealand (remote activation code) on the telephone keypad, wait to hear the fax machine turn on (chirping sounds) and then hang up.
  
  
• If you answer on the handset of the fax machine and hear a beep every 3 seconds or silence, press the Fax Start or Start/Copy key on the control panel of the fax machine and then hang up the handset.
  
  
• If you answer a call on an "extension" phone during the F/T Ring Time, you will hear the F/T ring tones.
  To release the call from the fax machine, press #51 or #91 for New Zealand (remote deactivation code) on the telephone keypad and you can speak to the calling party.
  
  
• If you pick up the handset of the fax machine during the F/T ring time, you may talk to the calling party immediately.

Kindly check your incomming line connected in Line In port of machine . And change your receive mode as TEL/FAX .

Again the same will happen the probelm related to its Line Interface Unit. Change it and check, your problem must be solve.

Hi ...

There are situations when fax interrupts the telephone conversation. The possible cause of this issue is Remote RX feature on MP 780. There are 3 possible solutions to these problems which are listed below:

I) Change Remote RX ID on MP780

1. Confirm the <Fax> button light is lit. If the light is not lit, press the <Fax> button.
   
   
2. Press <Menu> button. [RECEIVE MODE] will appear on the display.
   
   
3. Press < (left arrow) or > (right arrow) to select [RX SETTINGS].
   
   
4. Press <OK>. [ECM RX] will appear.
   
   
5. Press the < (left arrow) or > (right arrow) to select [REMOTE RX].
   
   
6. Press <OK> twice. The current Remote RX ID number will appear.
   
   
7. Press < or > to select the desired Remote RX ID number. The options are from 00 to 99.
   
8. Alternatively, you can press the numeric keypad to select the number.
   
9. For example, to select [38], press <3> and then press <8>.
   
   
10. Press <OK>.
    
    
11. Press <Stop/Reset> to return to standby mode (date and receive mode will appear).

II) Turn off Remote RX on MP780

1. Confirm the <Fax> button light is lit. If the light is not lit, press the <Fax> button.
   
   
2. Press <Menu> button. [RECEIVE MODE] will appear on the display.
   
   
3. Press < (left arrow) or > (right arrow) to select [RX SETTINGS].
   
   
4. Press <OK>. [ECM RX] will appear.
   
   
5. Press the < (left arrow) or > (right arrow) to select [REMOTE RX].
   
   
6. Press <OK>. The current Remote RX option [ON] will appear.
   
   
7. Press < or > to select [OFF].
   
   
8. Press <OK>.
   
   
9. Press <Stop/Reset> to return to standby mode (date and receive mode will appear).

III) Choosing a receive mode MP780
If you want to receive only faxes automatically with your machine, or you have a dedicated telephone line for fax use only:

• Select [FAX ONLY MODE].
  
  When you receive a fax call: The machine will receive the fax automatically.
  When you receive a voice call: You will not be able to answer the call.

If you receive mainly voice calls and sometimes faxes, or you want to receive faxes manually:

• Select [MANUAL MODE].
  
  When you receive a fax call: The telephone will ring. Pick up the handset and if you hear a beep, press <Black> or <Color> on the machine to receive the fax.
  When you receive a voice call: The telephone will ring. Pick up the handset to answer the call.
  For remote receiving: If you are far from your machine, dial 25 (the remote receiving ID) on your telephone to receive faxes. (Telephone being used, such as a base station for a cordless phone, must be connected through the MP780 for the remote receiving function to work.)

If you want to receive voice messages on your answering machine and receive faxes automatically:

• Select [ANS.MACHINE MODE].
  
  When you receive a fax call: First the answering machine connected to your MP780 will respond to an incoming call, and then the MP780 will receive faxes automatically.
  When you receive a voice call: The answering machine connected to your MP780 will respond to an incoming call.

If you want to receive faxes automatically as well as voice calls:

• Select [FAX/TEL AUTO SW].
  
  When you receive a fax call: The machine will receive the fax automatically.
  When you receive a voice call: The machine will ring. Pick up the handset to answer the call.

If you have subscribed to a Distinctive Ring Pattern Detection (DRPD) Service with your telephone company (US only):

• Select [DRPD].
  
  When you receive a fax call: The machine will ring according to the ring pattern you have chosen and receive the fax automatically.
  When you receive a voice call: The machine will ring according to the ring pattern you have chosen. Pick up the handset to answer the call.

Dont' forget to vote if this helps .... Cheers :)

Contact your telephone provider and see if they can offer you a second number for the line and "destinctive ring".
If your fax unit supports this feature, the fax number can do a double-ring where the normal number does a normal ring. The fax unit would then pick up double-ring calls.

Receive Mode Settings Select from the following receive mode options to suit your needs. Once you've decided on which receive mode to use, follow the below instructions to set the receive mode using the operation panel. Receive Mode Setting

1. Press the <FAX> button to enter Fax mode.
   
2. Press <Menu>.
   
3. Press the right or left arrow button to select [Receive mode settings], then press the <OK> button.
   
4. Press the up or down arrow to select the receive mode that best suits your needs, then press <OK>.
   
   

Types of receive mode
Select the receive mode according to your needs.
Receive mode
Purpose
FAX/TEL AUTO SW When you want to receive faxes automatically as well as voice calls. FAX ONLY MODE When you want to receive only faxes automatically with your machine, or have a dedicated telephone line for FAX use only. DRPD When you have subscribed to a DRPD service with your telephone company. MANUAL MODE When you receive mainly voice calls and sometimes faxes, or want to receive faxes manually. ANS.MACHINE MODE When you want to receive voice messages on your answering machine and receive faxes automatically. FAX/TEL auto switch
FAX :
The machine does not ring but will receive the fax automatically. Voice call :
The phone attached to the machine will ring. Pick up the handset to answer the call. Note:

• Ring start timing and Telephone ring length can be specified in FAX/TEL auto switch in the Receive mode settings.
  
• If you want the telephone to ring when it receives a fax, connect a telephone to your machine and enable the Incoming ring settings in RX settings.
  
• The phone attached to the machine may not ring depending on the telephone type you are using.

FAX only
FAX * :
The telephone does not ring. The machine will receive the fax automatically. Voice call :
You will not be able to answer the call. * If you want the telephone to ring, connect the telephone to your machine and enable the Incoming ring settings in RX settings menu.


DRPD
FAX :
Your telephone line will ring according to the ring pattern you have chosen and receive the fax automatically. Voice call :
Your telephone line will ring according to the ring pattern you have chosen. Pick up the handset to answer the call. Note: Specify the FAX pattern in the DRPD: Set FAX ring pat. in RX settings menu.

Manual RX
FAX :
The telephone attached to the machine will ring. Pick up the handset and if you hear a beep tone, press the <Color> or <Black> button on the machine to receive the fax. Voice call :
The telephone attached to the machine will ring. Pick up the handset to answer the call. Note: If you are far from your machine, you can use the remote receiving function to receive faxes. Pick up the handset of the telephone connected to the machine and press 25 (the remote receiving ID).

Ans. machine connect
FAX :
First the answering machine connected to your machine will respond to an incoming call, and then the machine will receive faxes automatically. Voice call :
The answering machine connected to your machine will respond to an incoming call. Note:

• Set the answering machine to answer on the first or second ring.
  
• The entire message should be no longer than 15
  

Note: check your equipment for:
Fax machine must be connected to an answer machine

Receiving a fax automatically:
1 Make sure the Fax Auto Answer light is on.
2 To set the number of telephone rings before the printer automatically receives faxes,
Receiving a fax with an answering machine
When a telephone ring is detected, the answering machine picks up the call.
• If the printer detects a fax, it receives the fax and disconnects the answering machine.
• If the printer does not detect a fax, the answering machine receives the call.
2 Set the answering machine to answer incoming calls before the printer does.
For example, if you set the answering machine to answer calls after three rings, set the printer to answer calls
after five rings.
3 To set the number of telephone rings before the printer automatically receives faxes.