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DLM4000 User Guide
PN 161-09997-003A
Feb 2005
DLM4000 Troubleshooting
When connecting modem to terminal emulation program, modem does not respond:
1. Ensure the modem is connected to the COM port that the terminal emulation program is using.
2. Check that the COM port is free and no other devices are using it such as an internal modem.
3. Make sure the cable connecting the modem to the PC is the correct cable. Refer to the cable requirements section of
the manual.
4. Try re-starting the terminal emulation program.
5. Make sure the proper power supply is being used. The DLM4000 requires a 9 VAC power supply for proper operation.
When sending a text file with the modems, the received text has missing characters.
1. Ensure that the communications program’s baud rate matches that of the DLM4000.
2. Make sure the word length is set to a 10bit word and not an 11-bit word. Refer to DLM4000 requirements section of
manual.
A programmed phone number is stored in the modem, but when carrier is lost the modem does not redial.
1. The DLM4000 modem is capable of dialing a stored phone number when the modem is powered up only and will not
redial upon loss of carrier.
2. If the modem has Auto Answer Dial Back board installed, most likely there is no stored phone number or the
configuration is incorrect. Refer to Auto Answer Dial-Back section of the manual.
I am trying to connect to the DLM4000 modem with my PC modem, but it does not work.
Data-Linc Group does not recommend or support the use of another manufacturer’s modem. It is recommended that a
second DLM4000 be purchased for optimal connection.
The leased-line DLM4000 modems are powered up, but they do not try to connect.
1. The modems are most likely not configured for leased line operation.
2. Refer to the DLM4000 requirements for the proper jumper setting in the modem.
The DLM4000 modems have carrier, but my PLCs are not communicating.
1. Make sure that the PLC is setup to use a 10-bit word and that the baud rate matches that of the modem.
2. Verify that the modem cabling is correct. If Data-Linc Group supplies the cable, verify the cable pinout per the supplied
cable diagram. If a cable diagram was present, contact Data-Linc Group Group.
3. Ensure that the PLCs are setup and the addressing is correct. The DLM4000 modem does not require handshaking
and this should not be enabled in the PLC.
4. If a problem is suspected with the DLM4000, a loopback test should be ran if possible. Refer to the section on Setting
Up And Using HyperTerminal For Testing.
When in leased line mode the DLM4000 modems are constantly trying to establish communications with each
other.
1. Verify that the communications line being used is an analog voice grade line and not a digital line.
2. Confirm that the leased line connection at both DLM4000 locations is connected properly. The two center pins of the
jack are the correct pins.
3. Make sure that the leased line is a two wire leased line and not a four wire. The DLM4000 will not operate on a four
wire leased line.
4. Verify proper modem operation with a bench test and a phone patch cord.
5. Is there a possible source of electrical noise near the modem such as a variable frequency drive?
6. If the lines have been provided by the telephone company, check with them to verify line integrity.
7. Are surge suppressors being used? Try removing them and see if the modems connect properly. Some surge devices
may prevent communications.
