There's a method to the madness of checking your modem cable.
There are several ways you could determine if your cable is OK, but the modem tricks you because they "fake" carrier detect so that some terminal programs respond properly.
Here I try to explain one way to do a cable test using the "Cable Test" program I wrote for MUBBS.
You need to think about this a bit (this won't take 2 minutes and then you give up)....
In "Cable Test" 0 means NO CARRIER, so when you first turn your modem ON there should be NO CARRIER, HOWEVER..... most modems show a carrier with FACTORY settings! Then your STUPID (PC) terminal program thinks all is OK and goes on with its life (at least STUPID IBM terminal programs do)
SO..... when you turn your modem on with "factory" settings, it will show a "1".
What you are looking for is a "0" AFTER YOU SEND AT&C1 or some other command that tells the modem to send carrier detect out PROPERLY (reflecting carrier detect properly).
So, take a 9 Volt battery and connect it between pin 7 & 8 on your connector that goes to the modem (the DB-25), and then reverse POLARITY and see if the thing changes 0 to 1, it should if your cable is wired OK. (the cable comes from your MAC, then to your BATTERY, the modem is DISCONNECTED at this point).
Pin 8 is CARRIER DETECT from ALL MODEMS.
Pin 7 is GROUND.
What you are doing is SIMULATING what the modem does.
As you reverse polarity (plus to minus) then the Mac should sense this and it should show up on the screen. This tells you that the cable Pin 8 is connected to the Mac OK.
If your cable is not correct, then you need to STRIP & TAPE & CHANGE your cable (or whatever fixes it, like get a new one for $5???).
A 9V battery does NOT have enough POWER to hurt your Mac's ports, so don't start whining about blowing up your Mac, I'm really tired of whimps saying they are going to blow something up (yes, if this was TV your Mac would smoke, catch fire and blow up your whole neiborhood).
Try that first. If you dont have wire to do this, GET SOME!
If the cable's OK, then your modem strings need to be tested out.
You will have to try all the standard stuff like AT&C1, AT&C0 or whatever. When you get the string correct, you will see a "0" appear (you have to start your terminal program, type in the commands, then exit it and start Cable Test. You can't run them at the same time).
Use something like Red Ryder or ZTerm that don't mess with the modem when you QUIT the program. Watch your modem lights to see if your Terminal Program sends anything to the modem when you QUIT the program. Some of these "we cater to stupid users" type programs send a ATZ to the modem just before quitting!
Here's another problem I ran into:
I picked up a modem cable from the swapmeet for $5, when I checked it out it wasn't working correctly with the MODEM connected, but with the 9V battery everything showed good! I used my "good" cable to make sure I wasn't going crazy.
It ends up that Pin 8 was connected DIRECTLY to Pin 5 (another output that stays +10V on most modems). So when carrier detect (Pin 8) went -10V, Pin 5 forced a +10V on it and the circuit decided +6V was the winner. So when I connected to the modem, it was always +6V or +10V but never went -10V !
What does all this mean? Take a OHM METER *OR* a light bulb and a battery and check to see if any other pins are connected to Pin 8 !
Give it some BRAIN power, don't just think that you will do it in 1 second and then give up.
