Hi all,

I just got a Western Electric 2554BMP: wall mounted, chrome cradle, manufacture year: 1976

It rings and answers calls perfectly. It gets a dial tone, but it has problems dialing.

All of the keys produce a tone, but only "*", "0" and "#" will "register".

Here is what happen.

- pick up the receiver, get a dial tone
- press "1" or any key up to "9": a key tone is produced, however dial tone continues (that is not normal, right?)
- press "0" or "*" or "#": key tone is produced, and dial tone stops as expected.

It would seem that only 9 of the 12 keys are actually "heard", although they all produce a tone.

This is my first exposure to old telephone technology, so I don't really know where to start.
Any help will be greatly appreciated!

Thanks,
Mike

Try reversing the tip & ring (Red & Green)wires on the incoming cable. Some earlier dial pads were polarity sensitive.

Thanks MooreTel.

I should have mentioned that I already tried that, but it had no effect. Even with the polarity reversed, only 3 of 12 keys work.

Thanks,
Mike

Try cleaning the dial contacts with a either typing or copy paper, you can use alcohol if they're real bad.

Next step would be to check the wiring on THAT phone with another 2554 or 2500 set. Of course the dial pad could be defective. Changed a few in my day.

Thanks/Merci!

I guess the next step is to take apart the dialpad and see what can be done. I'll make sure to report on my progress.

Mike.

Oh, and I will also check the wiring (je vais verifier le cablage ).

I just found the right resource from another post:
https://www.sundance-communications.com/cgi-bin/ultimatebb.cgi?/ubb/get_topic/f/32/t/000076.html

The frequencies could be off. When you hold down two keys in a row, or two keys in a column, do you hear a single tone?

Do you have another touch tone set, and 4 hands? Take them both off hook at the same time, press 1 and 2 on both sets at the same time, and listen to the resulting "beat" frequency. If it is wavering, the tuning is off. Compare with 1 and 4 as well.

The transformers have a slug in the center that can be turned to retune, BUT, it is usually a triangular slot, and a metal instrument inserted into it will change the frequency while tuning. We used to shave an orange stick to fit, so no interference with metal, and less chance of shattering the tuning slug.


.

Aha! That's very interesting.

Yes, I hear only one single tone when I press two rows or two columns keys at once.

I only have one of those old sets to work with, however I can easily reproduce the individual tones at the right frequency from my computer for comparison.

I have found the frequencies here: https://en.wikipedia.org/wiki/Telephone_keypad

I'll try that.

Thanks,
Mike

Mike, the contacts that you should be concerned with are the ones around the sides of the dial, not the ones on the back. Since each button's frequency is actually a combination of two tones, one dirty contact can distort the tone generated from several buttons. It is fairly unusual for so many of these contacts to fail at the same time, but if the phone has been stored/inactive for a long period, anything is possible.

Remember that you have a 3 x 4 matrix of tone combinations, so with only one row of buttons working, you likely have 5-6 dirty contacts. Be cautious about attempting to tune the transformers. The tones are very, very precise and when you start messing with both transformers, you may never get a perfect match again using the human ear.

Thanks Ed!

I really appreciate all the feedback I am getting here. You guys are great!

Mike.

Now you know the mechanics behind DTMF: Dual-Tone Multi-Frequency

Mike/Ed

From what was described, I think the problem is that the bottom row contact is either jammed or shorted. It may just need to be gapped.

It's fixed!

First I verified that there were no shorts in the contacts, and I checked the continuity of the closing contacts. They all seemed OK, but I cleaned them anyway (I was surprised to find some spiderweb inside the dial pad). Still no improvement after that.

Then I compared the individual row tones against the correct frequencies from a software tone generator. It was difficult to tell, but they seemed a bit low to me. I adjusted one of the two transformers by only 1/2 turn clockwise, and bingo! All keys now work!

Big thanks to all who helped! I learned a lot in the process, it was fun, and I now have a great looking phone on my kitchen wall.

Mike

Well, that's great news. Thanks for letting us know how you made out.

I must say that in my 30 years in this business, I've never had to adjust the transformers on a dial. Dirty contacts have always been the issue with my experiences. I'm wondering if someone messed with them, since they are usually sealed at the factory with paint. We may never know.

Ed, I concur, however, I have had to retune several (3-4) that I'm pretty sure had broken paint seals from the phone hitting the floor tooooo many times. All hospitality room phones, fancy that!

Ed/Lightninghorse,

When I took out the dialpad, I found that the transparent plastic cover that goes in the back of it was held in place with some scotch tape that looked fairly recent. Someone had been in there before me for sure.

Thanks,
Mike

We purchased 2500 and Princess lease returns from AT&T salvage by the pallet - had to retune many pads. We would hook up a talk battery source, had a known good phone that could have a row or column jammed down with a chopstick, and then listened through the handset while holding the buttons down on the bad pad and adjusting the transformer. You determine which transformer controlled the low or high frequency by slipping a jeweler's screwdriver into the center to see which one changed frequency, then used the orange stick to make the adjustment.

While zero beating them by ear against a good phone might get you in the neighborhood, many service monitors (used by two-way radio techs) will do DTMF decode, as well as provide a tuning aid for adjusting DTMF encoders.

If you can get access to one that would probably be the easiest and most accurate way to do this.

Failing that, a software package like Spectrum Lab (https://www.qsl.net/dl4yhf/spectra1.html) and a Windows laptop would be the way I'd do it -- just be sure to run the sound card calibration routines first.

Did you notice the dates of the previous posts?

Gah...I noticed the DATE, but I'm apparently still in 2011.

I replied since they looked 'reasonably' current.

D'oh.