Vintage Touch Tone Won't Dial
November 29, 2010 11:55 AM   Subscribe

Vintage touch tone phone receives calls but won't generate tone.

I just bought this 1977 ITT K-2500 touch tone phone for $5 from Value Village. The phone rings and gets dial tone and sounds crystal clear when you receive a call, but it won't dial. When I push the buttons the dial tone gets quieter but there's no tone from pushing the button.
From the limited info I've found on Google, there may be some kind of issue with voltage or polarity or something, but reading wiring schematics (this one can be found in the link above) is not really my forte. I can open stuff up and use a soldering iron, but am clueless about how phones work. Is there an easy-ish way to make this a workable phone?
posted by chococat to Technology (6 answers total)
Polarity, most likely. Swap the two wires connected inside your home jack. (So if it's using red and black, hook them up black and red.) You'll need a screwdriver, not a soldering iron.

[Really? You *bought* an old touchtone phone?]
posted by lothar at 12:56 PM on November 29, 2010

Yeah, polarity -- happens with me all the time, I think because my answering machine reverses the polarity. Sometimes it's easier to reverse the wires in the jack. Acid test is, while listening through the headset and pressing a button, instead of a tone does the ambient audio diminish slightly in volume? Swap the wires, and presto!

Opening it up, you'll then wonder, well what are these other wires for? The other two (if there's only four) may carry a little power to light up the dial of your Princess phone.
posted by Rash at 4:02 PM on November 29, 2010

Well, there's another old touch tone phone on that line already which works fine, so I don't know if it's the line. I tried switching the red and black anyway, no dice. And I switched every pair of red and black that I could find in the mess of wires coming out of the dialing pad inside the phone, to no avail.
posted by chococat at 5:15 PM on November 30, 2010

I think lothar had the right idea, but the wrong colors. The standard convention is for the first pair to be red/green, and the second to be yellow/black. So if you were to switch anything in the jack, it should be the red/green. (Granted not every house follows this convention.)

You shouldn't need to change any of the wiring inside the phone, just the wires inside the jack in the wall. If you take the jack out of the wall, you should be able to tell which wire goes to each pin--concentrate on the two in the center. I'll assume that your jack is wired correctly, and that the wire that connects to the pin just to the the right of center(when viewed from the back) is red, and the other is green, but if you have different colors, then just substitute them in.

If you have a multimeter, you can verify which wire is which--the green is earth (ground) and the red has negative 48 volts, give or take. So the positive lead to red, negative to green should give a negative voltage. If you get positive, your house is wired backwards, and you can either fix it at each jack, or at the point where the house wiring connects to the phone company's wiring (I'd recommend this). Then wire the phone back the way it was and everything should work!

If you don't have a multimeter, just swap the red/green in the jack and if that fixes it--you won't damage anything if it was wired correctly and you reverse it.

Most modern phones have circuitry to correct if the polarity's backwards, and old rotary phones didn't care, so it's not uncommon to see a home wired backwards, and the details you give are exactly the way old touch-tone phones behave with reversed polarity.

See wikipedia's Tip and Ring article for more background.
posted by yuwtze at 7:03 PM on December 1, 2010

Bingo, yuwtze.
Switching the red and GREEN did the trick. I opted to switch the wires only on the jack I'm using this phone with, because the main junction in the basement where all the lines come out of is a scary nest from the 1950's or earlier.
The thing that puzzles me is why other touch tone phones had worked, including a donut phone from late 70's, early 80's. Something about voltage?
Anyhow, thanks.
posted by chococat at 10:23 AM on December 2, 2010

Thanks everyone, I meant to say.
posted by chococat at 10:26 AM on December 2, 2010

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