Multitech MultiModem MT5656ZDX-Series User manual

MultiModem® ZDX
Model MT5656ZDX-Series
Voice/Data/Fax Modem
User Guide

Copyright and Technical Support
2 Multi-Tech Systems, Inc. MT5656ZDX User Guide
MultiModem® ZDX User Guide
MT5656ZDX, MT5656ZDX-V
S000248, Revision M
Copyright
This publication may not be reproduced, in whole or in part, without prior expressed written permission from Multi-Tech Systems, Inc. All
rights reserved. Copyright © 2013 by Multi-Tech Systems, Inc.
Multi-Tech Systems, Inc. makes no representations or warranties with respect to the contents hereof and specifically disclaims any
implied warranties of merchantability or fitness for any particular purpose. Furthermore, Multi-Tech Systems, Inc. reserves the right to
revise this publication and to make changes in the content hereof without obligation of Multi-Tech Systems, Inc. to notify any person or
organization of such revisions or changes.
Revision
Date
Description
K
06/03/11
Remove all references to CDs.
L
09/17/12
Updated RoHS.
M
12/16/2013
Added UL translations.
Patents
This device is covered by one or more of the following patents: 6,031,867; 6,012,113; 6,009,082; 5,905,794;
5,864,560; 5,815,567; 5,815,503; 5,812,534; 5,809,068; 5,790,532; 5,764,628; 5,764,627; 5,754,589; D394,250;
5,724,356; 5,673,268; 5,673,257; 5,644,594; 5,628,030; 5,619,508; 5,617,423; 5,600,649; 5,592,586; 5,577,041;
5,574,725; D374,222; 5,559,793; 5,546,448; 5,546,395; 5,535,204; 5,500,859; 5,471,470; 5,463,616; 5,453,986;
5,452,289; 5,450,425; D361,764; D355,658; D355,653; D353,598; D353,144; 5,355,365; 5,309,562; 5,301,274.
Other patents pending.
Trademarks
MultiModem, Multi-Tech, and the Multi-Tech logo are trademarks of Multi-Tech Systems, Inc. All other brand and product names are
trademarks or registered trademarks of their respective companies.
Contacting Multi-Tech
Knowledge Base
The Knowledge Base provides immediate access to support information and resolutions for all Multi-Tech products. Visit
http://www.multitech.com/kb.go.
Support Portal
To create an account and submit a support case directly to our technical support team, visit: https://support.multitech.com
Support
Business Hours: M-F, 9am to 5pm CT
Country
By Email
By Phone
Europe, Middle East, Africa:
[email protected]
+(44) 118 959 7774
U.S., Canada, all others:
[email protected]
[phone] or [phone]
World Headquarters
Multi-Tech Systems, Inc.
2205 Woodale Drive
Mounds View, Minnesota 55112
Phone: [phone] or 800-328-9717
Fax: [phone]
Warranty
To read the warranty statement for your product, please visit: http://www.multitech.com/warranty.go.

Table of Contents
Contents
Chapter 1 –Product Overview ..........................................................................................................................5
Overview ................................................................................................................................................................5
Related Documents................................................................................................................................................5
Package Contents...................................................................................................................................................5
You Need ................................................................................................................................................................6
Technical Specifications .........................................................................................................................................6
Chapter 2 - Installation.....................................................................................................................................8
Analog Telecom Safety Warnings...........................................................................................................................8
Installing on a Windows Computer........................................................................................................................9
Connecting the Modem to Your System..........................................................................................................9
Connecting Voice (Voice option only) ...........................................................................................................10
Installing the Modem Driver on Windows.....................................................................................................11
Connecting to the Internet ............................................................................................................................11
Dial-Up Networking .......................................................................................................................................11
Installing on a Linux Computer.............................................................................................................................12
Connecting the Modem and Verifying Operation .........................................................................................12
Using the Modem Connect to the Internet ...................................................................................................12
Calling the ISP ................................................................................................................................................12
Chapter 3 - Operation.....................................................................................................................................14
About the LED Indicators......................................................................................................................................14
Configuring Your Software ...................................................................................................................................15
Configuring Your Modem.....................................................................................................................................15
Chapter 4 - Troubleshooting ...........................................................................................................................16
Indicators Don’t Light Up .....................................................................................................................................16
Modem Does Not Respond to Commands...........................................................................................................16
Modem Dials but Cannot Connect.......................................................................................................................18
Modem Disconnects while Online .......................................................................................................................19
Modem Cannot Connect When Answering..........................................................................................................19
Garbage Characters on the Monitor ....................................................................................................................19
Modem Doesn’t Work with Caller ID ...................................................................................................................19
Appendix A –Regulatory Information.............................................................................................................20
FCC Part 68 Telecom ............................................................................................................................................20
47 CFR Part 15 Regulation Class B Devices...........................................................................................................21

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4 Multi-Tech Systems, Inc. MT5656ZDX User Guide
Industry Canada Class B Devices ..........................................................................................................................21
Canadian Limitations Notice ................................................................................................................................22
EMC, Safety, and R&TTE Directive Compliance ...................................................................................................22
International Modem Restrictions .......................................................................................................................23
Waste Electrical and Electronic Equipment Statement .......................................................................................23
WEEE Directive ..............................................................................................................................................23
Instructions for Disposal of WEEE by Users in the European Union .............................................................23
Restriction of the Use of Hazardous Substances (RoHS)......................................................................................24
Information on HS/TS Substances According to Chinese Standards....................................................................25
Information on HS/TS Substances According to Chinese Standards (in Chinese)................................................26
依照中国标准的有毒有害物质信息 ...........................................................................................................26
Appendix B –Upgrading the Modem ..............................................................................................................27
Upgrade Overview................................................................................................................................................27
Step 1: Identify the Modem Firmware ..........................................................................................................27
Step 2: Identify the Current Firmware Version .............................................................................................27
Step 3: Download the Upgrade File...............................................................................................................28
Step 4: Extract the Upgrade Files...................................................................................................................28
Step 5: Upgrade the Modem’s Firmware ......................................................................................................28
Step 6: Restore Your Parameters...................................................................................................................28
Index .............................................................................................................................................................29

Multi-Tech Systems, Inc. MT5656ZDX User Guide 5
Chapter 1 –Product Overview
Overview
Multi-Tech MT5656ZDX and MT5656ZDX-V modems are compatible with the ITU-TV.92 protocol that provide
quick connections, downstream transmissions at speeds up to 56K bps, and upstream transmissions at speeds up
to 48K bps when connected to V.92-compatible Internet Service Providers. The V.92 protocol is able to send
downstream from the Internet to your computer at these speeds because data on the telephone network
typically is converted from digital to analog only once before it reaches your modem. Upstream transmissions and
transmissions between client modems are limited to 33.6K bps, as are upstream transmissions that are converted
more than once on the telephone lines.
Modem features include Plug and Play operation. In standard mode, the modem can store up to four command
lines or telephone numbers of up to 40 characters each in nonvolatile memory. Other modem capabilities include
modem-on-hold, AT&T calling card tone detection, pulse and tone dialing, adaptive answer, V.42bis and V.44 data
compression, and self-resetting lightning protection.
Please note that some V.92 features are turned off in the factory default configuration, and may need to be
turned on, depending on your needs.
Related Documents
Download related documents from www.multitech.com/man.go.
●AT Command Reference Guide (S000273)
●+V Voice Command Developer's Guide (S0000099)
●Fax Enhancements (S0000279)
●Fax Developer's Guide Classes 2 and 2.0/2.1 (S0000239)
●Fax Developer's Guide Classes 1 and 1.0 (S0000262)
●Fax Overview Developer's Reference (S0000265)
Package Contents
●One MultiModem ZDX (MT5656ZDX)
●One set of four self-adhesive rubber feet
●One power supply
●One RS-232 cable (a DB9F to DB25M serial cable)
●One RJ-11 telephone cable

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6 Multi-Tech Systems, Inc. MT5656ZDX User Guide
You Need
●A computer with an available serial port
●A nearby AC power outlet
●A nearby phone jack
●Optional: If you want speakerphone functions along with the ability to record sound or .WAV files through the
sound card at the same time, you need:
●One stereo PC microphone
●One stereo male to male patch cord
●One sound card
●Speakers
Technical Specifications
Feature
Description
Server-to-Client Data Rates
V.90 speeds when accessing a V.90 or V.92 server 1
Client-to-Server Data Rates
Up to 50Kbps when accessing a V.92 server1; otherwise, the same as client-
to-client data lines.
Client-to-Client Data Rates
33600,31200, 28800, 26400, 24000, 21600, 19200, 16800, 14400, 12000,
9600, 7200, 4800, 2400, 1200, 0-300 bps
Fax Data Rates
14400, 12000, 9600, 7200, 4800, 2400, 1200, 0-300 bps
Data Format
Serial, binary, asynchronous
Modem Compatibility
ITU-T V.92, V.90, V.34 enhanced, V.34, V.34bis, V.32, V.22bis, V.22; Bell
212A and 103; ITU-T V.21; V.42, V.42bis, V.44
Fax Compatibility
T.4, T30, V.21, V.27ter, V.29, V.34, V.17; TIA/EIA 578 Class 1 and Class 2,
TR29.2
Video Compatibility
ITU-T V.80 for H.34 video conferencing
Voice Compatibility
AT+V/TAM command set
Voice Mode Sampling
Up to 44.100 KHz (down-sampled to 11.025 KHz)
Error Correction
ITU-T V.42 (LAP-M or MNP 4)
Data Compression
ITU-T V.44 (4:1 throughput), V.42bis (4:1 throughput), MNP 5 (2:1
throughput)
Speed Detection
Automatic speed detection and switching between available speeds
Speed Conversion
Serial port data rates adjustable to 300; 1200; 2400; 4800; 9600; 19,200;
38,400; 57,600; 115,200 bps
Operation Modes
Fax online modes, full duplex data over dial-up; voice
Flow Control
XON/XOFF (software), RTS/CTS (hardware)
Intelligent Features
Plug and play, full AT command compatible, autodial, redial, repeat dial,
pulse or tone dial, dial pauses, auto answer, adaptive answer; EIA extended
auto mode; caller ID, adaptive line probing; automatic symbol and carrier
frequency during start-up, retrain and rate renegotiation, DTMF detection,
call status display, auto-parity and data rate selections, keyboard-controlled
modem options, non-volatile memory, US Caller ID reporting; quick-connect
startup, TAPI compliant.
Command Buffer
40 Characters

Chapter 2 - Installation
Feature
Description
Transmission Level
-11 dBm (North America and Pan Euro) - varies by country setting
Frequency Stability
±0.01%
Receiver Sensitivity
-43 dBm under worst-case conditions
AGC Dynamic Range
43 dB
Connectors
Two RJ-11 phone jacks, DB25F RS-232C connector, power connector
Cables
One modular telephone cable
Diagnostics
Local analog loop, local digital loop, remote digital loop
Speaker
Speaker for call progress monitoring
Speaker and Microphone Jacks
MultiModemZDXV
Manual Controls
Power switch
Environmental
Temperature range 0°–50°C (32°–120°F); humidity range 20–90% (non-
condensing)
Storage Temperature
-10° to +85°C (14°- 185° F)
Power Consumption
150 mA @ 9 VDC
Dimensions
10.8 cm wide x 14.8 cm long x 2.9 high (4.25” × 5.8” x 1.15”)
Weight
224 g (8 oz)
Operating Systems
Tested for use with Windows 2000+ and Linux (2.2.x kernel)
Warranty
2 years
1Though these modems are capable of 56K bps download performance, line impairments, public telephone
infrastructure and other external technological factors currently prevent maximum 56K bps connections.

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Chapter 2 - Installation
Analog Telecom Safety Warnings
Before servicing, disconnect this product from its power source and telephone network. Also:
●Never install telephone wiring during a lightning storm.
●Never install a telephone jack in wet locations unless the jack is specifically designed for wet locations.
●Use this product with UL and cUL listed computers only.
●Never touch uninsulated telephone wires or terminals unless the telephone line has been disconnected at the
network interface.
●Use caution when installing or modifying telephone lines.
●Avoid using a telephone during an electrical storm. There may be a remote risk of electrical shock from
lightning.
●Do not use a telephone in the vicinity of a gas leak.
CAUTION: To reduce the risk of fire, use only 26 AWG or larger UL Listed or CSA Certified telecommunication
line cord.
Avertissements de sécurité télécom analogique
Avant de l'entretien, débrancher ce produit de son réseau d'alimentation et de téléphone. également:
●Ne jamais installer du câblage téléphonique pendant un orage électrique.
●Ne jamais installer de prises téléphoniques à des endroits mouillés à moins que la prise ne soit conçue pour
de tels emplacements.
●Utilisez ce produit avec UL et cUL ordinateurs répertoriés seulement.
●Ne jamais toucher fils ou des bornes téléphoniques non isolés à moins que la ligne téléphonique n'ait été
déconnectée au niveau de l'interface réseau.
●Faire preuve de prudence au moment d'installer ou de modifier des lignes téléphoniques.
●Éviter d'utiliser le téléphone pendant un orage électrique. Il peut y avoir un risque de choc électrique causé
par la foudre.
●N'utilisez pas un téléphone à proximité d'une fuite de gaz.
ATTENTION: Pour réduire les risques d’incendie, utiliser uniquement des conducteurs de télécommunications
26 AWG au de section supérleure.

Chapter 2 - Installation
Installing on a Windows Computer
Connecting the Modem to Your System
Turn off your computer. Place the modem in a convenient location, then connect it to your computer’s serial port,
to the phone line, to AC power, and to your phone (phone is optional).
1. Connect the Modem to Your PC (RS-232 Connection).
Plug one end of the RS-232 serial cable into the RS-232 connector on the modem, and plug the other end into
a serial port connector on your computer.
2. Connect the Modem to the Telephone Line (Line Connection)
Plug one end of the phone cable into the modem’s LINE jack and the other end into a phone wall jack. The
phone cable is included with your modem.
Note: The LINE jack is not interchangeable with the PHONE jack. Do not plug the phone into the LINE jack
or the line cable into the PHONE jack.
3. (Optional) Connect the Modem to the Phone.
For voice-only calls, plug a phone into the modem’s PHONE jack.
4. Connect the Power
Make sure the power switch is set to OFF. The power switch is located on the side panel of the modem.
Plug the power supply into a power outlet or power strip. Plug the other end into the PWR jack on the
modem.
CAUTION: Use only the power supply cable supplied with the modem. Use of any other power supply voids
the warranty and can damage the modem.

Chapter 2 - Installation
10 Multi-Tech Systems, Inc. MT5656ZDX User Guide
About Power Connection, Surge Protectors, and Lightning
Power surges and other transient voltages on power lines, such as those caused by lightning strikes, can
damage or destroy your modem. Therefore, we recommend that you plug the modem into a surge protector
rather than directly into a wall outlet, preferably a surge protector that provides protection against electrical
spikes on the phone line as well as on the power line. Note that not even a surge protector can guard against
damage from a nearby lightning strike. During an electrical storm, it is safest to unplug your computer
equipment from both the power outlet and the phone line.
Power-On Test
Test the modem by turning it on (an on-off switch is located on the side panel). When you apply power, the
modem performs a diagnostic self-test. The PWR indicator lights; and if a terminal program is running, the TR
indicator also lights. If this does not happen, check that the power switch is on, the power supply is solidly
connected, and the AC outlet is live. If these measures do not work see the Troubleshooting chapter.
The Federal Communications Commission (FCC) and Industry Canada impose certain restrictions on equipment
connected to public phone systems. For more information, see Appendix A.
Connecting Voice (Voice option only)
1. Connect the Microphone
For voice mail or speakerphone applications, plug an unamplified microphone into the MIC jack on the side
of the modem. The microphone should have a stereo 1/8-inch (3.5mm) mini plug. Do not use a monophonic
microphone.
2. Connect the Speaker
For speakerphone or voice mail applications, use a 1/8-inch (3.5mm) plug male-to-male stereo patch cord to
connect the SPKR jack on the side of the modem to the LINE IN jack on your sound card. If your sound card
does not have a LINE IN jack, use its MIC jack. The stereo male-to-male patch cord can be purchased at a
local PC retail store.
If you do not have a sound card, you can plug an amplified speaker directly into the SPKR jack.

Chapter 2 - Installation
Installing the Modem Driver on Windows
To install on Windows 2000 or newer:
1. Download the modem driver from http://www.multitech.com/support.go.
2. Make sure your modem is connected properly, and then turn on your computer. Windows should detect your
new modem and open the Welcome to the Found New Hardware wizard.
Note: If Windows cannot find a modem, your modem may be turned off, or it may be plugged into the wrong
connector on your computer. See Troubleshooting.
3. From the Browse function in the Install Wizard, point to the Temporary folder you created on your local PC to
store the driver that you downloaded from the Multi-Tech website. Windows installs and configures the
modem.
4. Click Finish to exit.
Connecting to the Internet
To access the Internet and Web via your modem, you must establish a dial-up account with an Internet service
provider (ISP). Your ISP should provide you with the following information:
●User name (also called user ID)
●Password
●Access number (the number you call to connect to the server)
●Host name and/or domain name
●Domain Name Server (DNS) server address
If you use the Internet for email and newsgroups, your ISP should also provide you with the following information:
●Email or POP mail address
●POP server address
●Mail or SMTP address
●News or NNT server address
Dial-Up Networking
Before you can connect to the Internet, you must set up a remote-node client program on your computer. The
Windows version is called Dial-Up Networking. Dial-Up Networking establishes your connection to the ISP’s
server, which is the shared computer that manages calls from clients (your computer) to the Internet. Most, if not
all, Windows browsers start Dial-up Networking automatically when you open them.
For instructions on how to set up Dial-Up Networking, consult your ISP or your operating system’s online help or
printed documentation. Many ISPs include with their service a program that will instruct and configure Dial-Up
Networking automatically for you.

Chapter 2 - Installation
12 Multi-Tech Systems, Inc. MT5656ZDX User Guide
Installing on a Linux Computer
These instructions describe how to install a modem on a computer using RedHat Linux 6.2 operating system.
Other versions of RedHat and other Linux operating systems should be similar. With Linux, you do not need
drivers for most standard external modems and most internal ISA bus modems. Programs in Linux commonly call
upon the port, rather than the modem.
Standard Linux Serial Port Definitions
Port Linux Port
Com 1 ttyS0
Com 2 ttyS1
Com 3 ttyS2
Com 4 ttyS3
Connecting the Modem and Verifying Operation
1. Connect the external modem to an available serial port.
2. Use the Terminal Program Minicom to verify operation. At the command prompt, type minicom –s and press
ENTER.
3. Select Serial port setup and press ENTER.
4. From Serial port setup, use the A key to access Serial Device, and then press ENTER.
5. Press ESC. You are now in the Minicom terminal.
6. Type AT and press ENTER. The screen should display OK to verify the operation. Alternately, dial a phone
number to verify line operation
To leave Minicom, press CTRL + A, and then press Z. 7. On the help menu, press X to exit.
Using the Modem Connect to the Internet
Linux allows different graphic user interfaces (GUI). The following steps use the Gnome Desktop GUI. It is
assumed that the ISP being called assigns the DNS and IP addresses.
1. Select the Gnome Footprint from the taskbar.
2. Select Internet from the menu.
3. Select Dialup Configuration Tool.
4. Select Add, and then click Next.
5. Enter the connection name and phone number, and then click Next.
6. Enter your user name and password, and then click Next.
7. Select Normal ISP if your ISP is not listed, and then click Next.
8. Click Finish.
Calling the ISP
1. Select the Gnome Footprint from the taskbar.
2. Select Internet from the menu.
3. Select RH PPP Dialer.

Chapter 2 - Installation
4. Select the connection name used when you connected to the Internet.
5. Click OK.
To use the system to answer calls, Linux requires other programs to be installed, such as Mgetty and Mgetty+Sendfax,
depending on requirements. Each vendor of Linux usually has adequate information on installing these programs.
Consult your Linux documentation for additional information.

Multi-Tech Systems, Inc. MT5656ZDX User Guide 14
Chapter 3 - Operation
Your Multi-Tech modem operates under the control of a communications program. For information on how to
use the modem with your communications program, please refer to the documentation provided with the data
communications program.
An experienced modem user can configure the program’s software to change the way the software interacts with
a modem and configure the modem to change the way it operates.
Front Panel
About the LED Indicators
The modem has ten LED indicators on the front panel that indicate status and activity:
TD Transmit Data
Flashes when the modem is transmitting data to another modem.
RD Receive Data
Flashes when the modem is receiving data from another modem.
CD Carrier Detect
Lights when the modem detects a valid carrier signal from another modem. It is on when the
modem is communicating with the other modem, and off when the link is broken.
OH Off-Hook
Lights when the modem is off-hook, which occurs when the modem is dialing, online, or
answering a call. The LED flashes when the modem pulse-dials.
TR Terminal Ready
Lights when a communication program is using the modem. It means the modem is ready for an
outgoing or incoming call. It goes off when the communication program disconnects the serial
port. When it goes off, a connected modem will disconnect.
Note: When you turn on the modem, the PWR indicator lights; and if a terminal program is running, the TR
indicator also lights.

Chapter 3 –Operation
Multi-Tech Systems, Inc. MT5656ZDX User Guide 15
Configuring Your Software
You may use either the communication program included with your modem or a third-party program.
Communication programs designed for Windows normally do not need to be manually configured, since they
obtain configuration information from Windows. Though each communication program is different, the following
procedure should work with most of them.
1. Turn on your computer and run your communications program.
2. Find the dialog box or menu that lets you select your modem. (In Windows Terminal select Settings | Modem
Commands; in HyperTerminal select File | Properties | Phone Number; and in the communications
program select Configure | General Configuration | Communication | Change Modem.
3. Choose your modem from the program’s modem list. If it isn’t listed, choose a generic modem and modify the
settings as necessary.
4. Change the modem initialization string, if necessary. The factory default configuration works well for most
purposes. To load the factory default configuration, use AT&F. To load a custom configuration that was saved
using the &Wcommand, use ATZ. Note that the Z command must be in a command string by itself. For a
Macintosh, the initialization string should include the &D0 command. If you do not want the modem to
always answer the phone, add S0=0 to the string. To use Caller ID with the modem, add S0=2 to the string
(Caller ID information is sent between the first and second rings, so the phone must ring at least twice
before the modem picks up the line). Depending on the software, you might have to end the string with a
carriage return character (^M).
Note: To change the modem’s default configuration, type new commands in the communication program’s
terminal window, adding the &W command to store them in the modem’s nonvolatile memory. For
instance, to create a default configuration for a Macintosh computer that turns off auto answer, type
AT&F&D0S0=0&W. The new configuration loads automatically whenever the modem is turned on or
receives the ATZ command.
5. Select the port the modem is connected to (normally COM1 or COM2).
6. Select your serial port speed. This can be labeled “maximum speed,” “DTE bps,” or “baud rate.” Ideally, if you
use data compression, you should set your serial port baud rate to four times the modem’s maximum
transmission speed or faster; however, few files can be compressed enough to require speeds that high,
and not all serial ports can handle speeds that high.
7. If the communication program has an autobaud selection, make sure it is disabled. Autobaud applies only to
older modems, and can cause problems if enabled.
8. If the program allows you to edit the no-connect messages (NO CARRIER, BUSY, NO ANSWER, NO DIAL TONE),
make sure there is no space between DIAL and TONE in NO DIAL TONE.
9. Refer to the program manual or online help for other configuration choices. In most cases you can accept the
default values.
Configuring Your Modem
Your modem normally is configured through Windows or through the communication program you are using. The
default settings work best for most purposes. However, you also can configure your modem by sending AT
commands to the modem. See the AT Command Reference Guide for a list of AT (data) commands and how to
use them.

Chapter 4 - TroubleshootingChapter 3 - Operation
16 Multi-Tech Systems, Inc. MT5656ZDX User Guide
Chapter 4 - Troubleshooting
Your modem was thoroughly tested at the factory before it was shipped. If you are unable to make a successful
connection, or if you experience data loss or garbled characters during your connection, check the list of
troubleshooting procedures before calling Multi-Tech.
If you experience problems, please check the following before calling Technical Support.
Indicators Don’t Light Up
When you turn on the modem, the PWR indicator and the terminal turn on. If the LEDs remain off, the modem is
probably not receiving power.
1. Make sure the modem’s power switch is on, especially if you normally turn the modem on by turning on a
power strip.
2. If the modem is plugged into a power strip, make sure the power strip is plugged in and its power switch is on.
3. Make sure the transformer module is firmly connected to the modem and to the wall outlet or power strip.
4. If the power strip is on and the modem switch is on, try moving the transformer module to another outlet on
the power strip.
5. Test that the outlet is live by plugging another device, such as a lamp, into it.
6. The modem or the DC power transformer may be defective. If you have another Multi-Tech modem, try
swapping modems. If the problem goes away, the first modem or the DC power transformer may be defec-
tive.
7. Call Technical Support for assistance.
CAUTION: Do not under any circumstances replace the transformer module with one designed for another
product. Doing so can damage the modem and void your warranty.
Modem Does Not Respond to Commands
1. Verify the modem is plugged in and turned on.
2. Verify you are issuing the modem commands from the data communications program, either manually in
terminal mode or automatically by configuring the software. (You cannot send commands to the modem
from the DOS prompt.)
3. Verify you are in terminal mode in your data communications program, then type AT and press ENTER. If
you get an OK response from your modem, your connections are good and the problem likely is in the
connection setup in your communications program.
4. If you don’t get an OK, the problem may still be in the communications program. Verify you have done
whatever is necessary in your software to make a port connection. Not all communication programs connect
to the COM port automatically. Some connect when the software loads and remain connected until the
program terminates. Others can disconnect without exiting the program. The modem’s TR indicator lights
to show that the software has taken control of the modem through the COM port.
5. Your communications program settings may not match the physical port the modem is connected to. The
serial cable might be plugged into the wrong connector—check your computer documentation to make sure.

Chapter 4 - Troubleshooting
Multi-Tech Systems, Inc. MT5656ZDX User Guide 17
Or you might have selected a COM port in your software other than the one the modem is physically
connected to—compare the settings in your software to the physical connection.
6. If the modem is on, the cable is plugged into the correct port, the communications program is configured
correctly, and you still don’t get an OK, the fault might be in the serial cable. Verify it is firmly connected at
both ends.
7. Is this the first time you have used the cable? If so, it may not be wired correctly. Check the cable description
on the packaging to Verify the cable is the right one for your computer.
8. Peripheral expansion cards, such as sound and game cards, might include a serial port preconfigured as COM1
or COM2. The extra serial port, or the card itself, may use the same COM port, memory address, or interrupt
request (IRQ) as your communication port. Be sure to disable any unused ports.
9. Windows 9x and 2000: Right-click on My Computer, select Properties from the menu, click on the Device
Manager tab, double-click on Ports, then double-click on the communication port your modem is connected
to. In the port’s Properties sheet, click on the Resources tab to see the port’s input/output range and
interrupt request. If another device is using the same address range or IRQ, it appears in the Conflicting
Device List. Uncheck Use automatic settings to change the port’s settings so they do not conflict with the
other device, or select the port the conflicting device is on and change it instead. If you need to open your
computer to change switches or jumpers on the conflicting device; refer to the device’s documentation.
The serial port might be defective. If you have another serial port, install the modem on it, change the COM port
setting in your software, and try again.
The modem may be defective. If you have another Multi-Tech modem, try swapping modems. If the problem goes
away, the first modem may be defective. Call Technical Support for assistance.

Chapter 4 - Troubleshooting
18 Multi-Tech Systems, Inc. MT5656ZDX User Guide
Modem Dials but Cannot Connect
There can be several reasons the modem fails to make a connection. Possibilities include:
●Lack of a physical connection to the telephone line.
●A missing dial tone.
●A busy signal.
●A wrong number.
●No modem at the other end.
●A faulty modem, computer, or software at the other end.
●Modem incompatibility.
You can narrow the list of possibilities by using extended result codes. Extended result codes are enabled by
default. If they have been disabled, include V1X4 in the modem’s initialization string, or in terminal mode enter
ATV1X4 and press ENTER. When you dial again, the modem reports the call’s progress.
●If the modem reports NO DIAL TONE, check that the modem’s phone line cable is connected to both the
modem’s LINE jack (not the PHONE jack) and the phone wall jack. If the cable looks secure, try replacing it. If
that doesn’t work, the problem might be in your building’s phone installation. To test the building
installation, plug a phone into your modem’s phone wall jack and listen for a dial tone. If you hear a dial
tone, your modem might be installed behind a corporate phone system (PBX) with an internal dial tone that
sounds different from the normal dial tone. In that case, the modem might not recognize the dial tone and
might treat it as an error. Check your PBX manual to see if you can change the internal dial tone; if you
can’t, change your modem’s initialization string to replace X4 with X3, which will cause the modem to
ignore dial tones (note, however, that X3 is not allowed in some countries, such as France and Spain).
●If the modem reports BUSY, the other number might be busy, in which case you should try again later, or it
might indicate that you have failed to add a 9, prefix to the phone number if you must dial 9 for an outside
line.
●If you must dial 9 to get an outside line, the easiest way to dial it automatically is to include it in the modem’s
dial prefix, e.g., ATDT9. Note the comma, which inserts a pause before the number is dialed. By inserting 9,
into the dial prefix, you do not have to include it in each directory entry.
●If the modem reports NO ANSWER, the other system has failed to go off-hook, or you might have dialed a
wrong number. Check the number.
●If the modem reports NO CARRIER, the phone was answered at the other end, but no connection was
made. You might have dialed a wrong number, and a person answered instead of a computer, or you might
have dialed the correct number but the other computer or software was turned off or faulty. Check the
number and try again, or try calling another system to Verify your modem is working. Also, try calling the
number on your telephone. If you hear harsh sounds, then another modem is answering the call, and the
modems might be having problems negotiating because of modem incompatibilities or line noise. Try
connecting at a lower speed.

Chapter 4 - Troubleshooting
Multi-Tech Systems, Inc. MT5656ZDX User Guide 19
Modem Disconnects while Online
●If you have Call Waiting on the same phone line as your modem, it can interrupt your connection when
someone tries to call you. If you have Call Waiting, disable it before each call. In most phone areas in North
America, you can disable Call Waiting by preceding the phone number with *70 (check with your local phone
company).
●You can automatically disable Call Waiting by including the disabling code in the modem’s dial prefix (e.g.,
ATDT*70,—note the comma, which inserts a pause before the number is dialed). To change the dial prefix
in Windows Terminal, select Settings | Modem Commands. To change it in HyperTerminal, select
Connect from the Call menu, click Dialing Properties, check This location has Call Waiting, and select the
correct code for your phone service.
●If you have extension phones on the same line as your modem, you or someone else can interrupt the
connection by picking up another phone. If this is a frequent problem, disconnect the extension phones
before using the modem, or install another phone line especially for the modem.
●Check for loose connections between the modem and the computer, the phone jack, and AC power.
●You might have had a poor connection because of line conditions or the problem might have originated on
the other end of the line. Try again.
●If you were online, it might have hung up on you because of lack of activity on your part or because you
exceeded your time limit for the day. Try again.
Modem Cannot Connect When Answering
Autoanswer might be disabled. Turn on autoanswer in your data communications program or send the command
ATS0=1 (ATS0=2 if you have Caller ID service) to your modem in terminal mode.
Garbage Characters on the Monitor
●Your computer and the remote computer might be set to different word lengths, stop bits, or parities. If you
have connected at 8-N-1, try changing to 7-E-1, or vice-versa, using your communications program.
●You might be experiencing line noise. Enable error correction, if it is disabled, or hang up and call again;
you might get a better connection the second time.
●Try entering the &V1 command to display information about the last connection, making a screen print
of the connection statistics, and checking for parameters that might be unacceptable.
Modem Doesn’t Work with Caller ID
●Caller ID information is transmitted between the first and second rings, if the modem is set to answer after
only one ring (S0=1), the modem will not receive Caller ID information. Check your initialization string, and if
necessary change it to set the modem to answer after the second ring (S0=2).
●Make sure that you have Caller ID service from your telephone company.

20 Multi-Tech Systems, Inc. MT5656ZDX User Guide
Appendix A –Regulatory Information
FCC Part 68 Telecom
1. This equipment complies with Part 68 of the 47 CFR rules and the requirements adopted by the ACTA. Located
on this equipment is a label that contains, among other information, the registration number and Ringer
Equivalence Number (REN) for this equipment or a product identifier in the format:
For current products: US:AAAEQ##Txxxx.
For legacy products: AU7USA-xxxxx-xx-x.
If requested, this number must be provided to the telephone company.
2. A plug and jack used to connect this equipment to the premises wiring and telephone network must comply
with the applicable 47 CFR Part 68 rules and requirements adopted by the ACTA. It’s designed to be
connected to a compatible modular jack that is also compliant.
3. The Ringer Equivalence Number (REN) is used to determine the number of devices that may be connected to
a telephone line. Excessive RENs on a telephone line may result in the devices not ringing in response to an
incoming call. In most but not all areas, the sum of RENs should not exceed five (5.0). To be certain of the
number of devices that may be connected to a line, as determined by the total RENs, contact the local
telephone company. For products approved after July 23, 2001, the REN for this product is part of the product
identifier that has the format US:AAAEQ##Txxxx. The digits represented by ## are the REN without a decimal
point (e.g., 03 is a REN of 0.3). For earlier products, the REN is separately shown on the label.
4. If this equipment causes harm to the telephone network, the telephone company will notify you in advance
that temporary discontinuance of service may be required. But if advance notice isn't practical, the telephone
company will notify the customer as soon as possible. Also, you will be advised of your right to file a complaint
with the FCC if you believe it is necessary.
5. The telephone company may make changes in its facilities, equipment, operations or procedures that could
affect the operation of the equipment. If this happens, the telephone company will provide advance notice in
order for you to make necessary modifications to maintain uninterrupted service.
6. If trouble is experienced with this equipment, please contact Multi-Tech Systems, Inc. at the address shown
below for details of how to have the repairs made. If the equipment is causing harm to the telephone
network, the telephone company may request that you disconnect the equipment until the problem is
resolved.
7. Connection to party line service is subject to state tariffs. Contact the state public utility commission, public
service commission or corporation commission for information.
8. No repairs are to be made by you. Repairs are to be made only by Multi-Tech Systems or its licensees.
Unauthorized repairs void registration and warranty.
9. If your home has specially wired alarm equipment connected to the telephone line, ensure the installation of
this equipment does not disable your alarm equipment.
If you have questions about what will disable alarm equipment, consult your telephone company or a
qualified installer.