Modem Troubleshooting
Using MacWise and OS X


What Internal Modem do I have in my Mac?
From the Apple Menu, select About This Mac and then More Info.
Then click on Modems. You will see the modem model and driver info.
The most difficult thing about troubleshooting modem problems is that every modem has a different AT command set. You will need to look at the manual for your specific modem to see what initialization string to use.

What Init String Should I Use?

The init string that seems to work with most modems is AT&F%C1. That is a command to reset your modem to factory defaults and then set it to MNP5 error correction. That option was added to MacWise version 10.7.995 as a button you can click to enable the option. (Dialer Menu / Modem Initialization Strings / MNP5 Data Compession.
If you have a previous version, you can just click on the Custom button and type the string in as AT&F%C1

After you have entered your modem init string...
Enter the phone number to dial (Enter QuickDial Number under the Dialer Menu)
Select QuickDial from the Dialer Menu to dial.
If you have entered an init string that your modem does not understand, you will get an error message.
If you get the error message, just hit return to cancel dialing. Then edit your init string.

Apple AT Commands for Internal Modems

Motorola SM56 internal Jump modem for G5 Macintosh
This is a software modem. Problems have been reported making a connection and dropping connections.
It appears that this virtual modem has backward compatibility issues when attempting to connect to older v.32 modems.If you are using MacWise version 10.7.21 or later, the problem is not with MacWise. You can download the AT Commands for this modem at
Then experiment with different initialization strings to get a good connection.
To enter the init string, select Modem Initialization Strings... from the Dialer Menu in MacWise.

Forcing a connection at v.32 with a baud rate of 9600
If your Mac is attempting to connect to an older style modem at the host, you can try forcing a connection at the old v.32 protocol at 9600 baud. Here are the modem initialization strings for various modems.

Motorola SM56 internal Jump modem for G5 Macs
at\n7%c1 +ms=v32b,0,9600,9600,9600,9600

Dash internal modem for G4 Macs

iMac G3 Internal 56k modem

Global Village 56K external modem

Modem Hangs Caused by Virex 7.5.x

March 2, 2005
by Rich Love

There are very few things that can cause a Mac running OS X to hang. It is the most stable operating system in existance. But Virex is one of the rare exceptions. Virex is an anti-virus program which is available free on the Apple Web site if you are a .Mac subscriber.

I recently installed Virex 7.5.1 on my Dual 2 gig G5 Mac.
It causes the G5 internal modem to hang the entire Mac when you try to do anything with the modem (dial with OS X, change fax answering status, dial with a terminal emulator.
It is a very hard freeze that requires powering off the Mac to get going again.
It is also very consistent (happens every time).

This appears to be an incompatibility between Virex 7.5.x and the Apple Internal modem on most newer Macs. This is a software modem with a Motorola Driver.

Another intermittent symptom is that the Mac will not boot. It gets stuck in the final stages of booting. While looking at the progress bar, it stops at the networking setup (file sharing or Internet stuff). If you have this booting problem and cannot get your Mac to boot, try several times. If it refuses to boot, hold the shift key down while booting and then run the Virex uninstaller. Then re-boot normally.

To uninstall Virex, double-click on the file "Virex_7.5.1.dmg" and run the uninstaller.

Modem Information for my G5 Mac:

Driver: MotorolaSM56K.kext (v1.2.0)
Hardware Version: Version 1.0
Interface Type: I2S
Country: B5 (United States, Latin America)
Modem Model: Jump
Modulation: V.92

There have been many reports about this problem on the MacFixit web site. If you want to look at the history of problems, go to MacFixit and do a search for "virex modem problems".