atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Telephone Repairs & Equipment trouble with trimline phone

My polarity test is from Radio Shack, a two line model with two LEDs. Yes, it has a short modular cord that plugs into a modular jack. The telephone tester I am using is a Teltone TLS3. I would hope that the TLS3 has the polarity correct as does the Radio Shack polarity tester. Otherwise, they are both wrong and phone is right. Interestingly, another Princess TT phone I tested also could not "dial out" but haven't had time to test it any further. Are you on to something, Arthur?

HMMM. My interest is piqued by this testing stuff. All of this is my humble opinion, of course.

It would seem very unlikely that someone would have gone to the trouble of opening the Trimline base (it's an AD-1, correct?) and fiddled with the internal wiring. The mounting cord is spade lugs at one end, and a large plug at the other, if I recall correctly. If someone would have wanted to defeat the TT dial, as you suggested, it would have been so much easier just to install the red & green leads reversed.

So, let's take a look at the connecting block. Has someone installed a modular adapter, or are you wiring the phone the original way, by fastening the leads under the screw heads?

In other words, how are you able to test the block using a modular tester?

I suggest that you get a VOM, set it to the 0-10 Vdc scale, and put the red lead on the + terminal of a D cell, and the black lead on the -terminal of the D cell. If the meter indicates + 1.5 volts, this will prove that the meter is functioning correctly.

Using the same hookup of leads, now put the meter into the 0-100 Vdc range, and test the red and green line wires at the connecting block. Put the red test lead on the GREEN (+) line wire, and the black test lead on the RED (-) line wire. You should read + 48 volts, approx. (Note, that's PLUS 48) if the house wires are poled correctly.

Remember, red is ring, which is negative, and green is tip, which is positive, in the wacky world of telephony.

Let us know the results.

OK, Arthur, here are the results. My VOM meter is OK. The Teltone TLS3 is OK. The problem is the modular jack that I am using in reverse to test the phones. Apparently, someone wired the pre-wired modular jack backwards. I was using this jack because I am using a modular tester (the Teltone TLS) with non-modular phones. To do this, I was using the modular jack in reverse, that is, inputting the test signal to the output of the jack and wiring the spade tip of the phone to the terminals of the jack. Thanks for enlightening me as to the real problem.

The jack is not wired incorrectly. You cannot use a 6p4c modular jack universally. The wires in a modular single-line mounting cord are reversed, with respect to the modular ends. The jack in the 625-series (and clones) blocks and the jack in the base of a telephone take this into consideration. Therefore you can't use an "output" jack as an "input" for testing, and expect to get proper polarity.

If you had taken a single-ended modular cord, plugged it into your dial tone source, and fastened its red and green leads to those of the Trimline, you would have gotten the proper polarity at the Trimline.

All of the above is not applicable to 8p8c plugs and jacks, because those are designed to have universal polarity.

I assume that the Trimline is now working correctly?

Yes, it is working correctly and you are right, the jack is probably wired correctly too. It is actually an old four-counductor jack, red, green, yellow, and black. The interesting footnote is that I ran into this problem again with a new old phone that was already modular but without a modular line cord. I discovered it was the line cord that was a problem even though it appears all 4 wires are in correct sequence. However, the phone dials out fine with two other modular cords.