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I have an AT&T 843 (3) line phone. I am trying to test it on a Teltone Simulator. Once I put the batteries in, the display turns on. The buttons work and I can get a ring out from the teltone. My only problem is that none of the (3) lines are coming up. The LEDs do not light up on the Line buttons. Is the phone bad or does the Teltone not support these phones? Any tips help!

As long as the Teltone can simulate a single telephone line, you should be able to check each line.

Now later versions of AT&T-branded No-KSU telephones allow you to disable individual telephone lines on each telephone.

I cannot find an online copy of the 843 owner's manual, but if the telephone does offer that feature and the cord you are using to connect the phone to the tester is good, then check to see if the lines have been deactivated.

The 843 needs an AC adapter for normal operation. Batteries are supposed to keep the unit functional, but not fully functioning, during a power failure. You may need to try to locate an adapter to really get a good test in as the unit may no longer be able to work on battery power.

The 843 has been off the market for several years, and it will not work properly if used in conjunction with the current set of at&t/VTech No-KSUs.