AT&T CS2554BMPF wall phone won’t dial out

[Darth Humorous]

I don't know if this is the right place for this, since it is not as old as most other phones (1980s?) and its guts are all electronic.

Anyway I have several various other phones, both electronic and electromechanical, and all, save two electronic and three electromechanical, work. The other two electronic phones have the same failure mode as the 2554 of this thread. The three electromechanical phones are ancient and require complete restorations. I am on VOIP (Ooma). I am suspicious of the dialing IC chips in all three of these phones. In the case of the 2554, there are two chips, and one looks like it is closely wired to the warbler ringer, and is relatively short (8 pins, WE2306T) so I'm sure that is what it is. the other chip (MOSTEK MK5373N with update[?] G) has 18 pins, and I believe it is for both the speech AND dialing circuits. For some reason, I am unable to pull up data sheets for the two chips., most likely due to the age of my computer.

Yes, I have checked line wiring at length. I am certain the fault lies with the phone, and I merely suspect the dialer chip, and don't know for certain.

Have any of you had this problem with any of your electronic phones (not the lines), and if so were you able to determine the cause(s)?

Thanks in advance for any help.

Mark

[dsk]

Most VOIP providers does not recognize rotary dials, or electronic versions of rotary dials (pulsed dialing)

If you put up a setup of a receiver, a 9V battery and the telephone in series you should be able to hear the pulses, or tones in the receiver.

[Darth Humorous]

Thanks for the reply. I just tried to post images of the phone. They show up as broken images. Could be my computer's age and older operating system. Maybe you can see the images? Or maybe they are too big to show up.

The CS2554BMPF phone is a touchtone phone with the option to select touchtone dialing or pulse dialing. I have it set to touchtone dialing. The other touchtone electronic phones work with the exception of the two I mentioned in my first post.

Mark

[Darth Humorous]

You are right about the VOIP not recognizing pulse dialing; at least Ooma doesn't. I found that out a couple of months ago.

Mark

[HarrySmith]

There is a topic here on posting photos. Everything you could need and more. It sounds like yours were just too big. Try resizing them.

How to here:

http://www.classicrotaryphones.com/forum/index.php?board=84.0

[Darth Humorous]

OK, 2nd try for images. If I understand correctly, the 3 images should appear at the bottom of this post.

Mark

[Darth Humorous]

Yay! It seems to have worked! There be pictures here! The pictures that finally posted are from ebay where I got the phone.

I managed to find a data sheet for the MK5373N IC, but it has a "1" instead of an "N" at the end. Still, it looks like the right thing. It describes the IC as a "Single chip DTMF and pulse dialer", and it has 18 pins. I believe this to be what the IC is, so no speech circuit is included. This drove me further examine the innards. I noted a "comparatively large" coil on the circuit board that I now believe to be part of the speech circuit. I don't know if speech circuits existed on chips in 1985, or maybe AT&T didn't trust them, or perhaps it was just economics.

I would like to take pictures of the innards and post them, but taking pictures and getting them onto my computer is an ordeal for me, so bear with me.

The phone is clean, inside and out, and nothing looks amiss. There is a glass fuse that isn't blown.

Mark

[Darth Humorous]

Trying a couple of more photos of the innards...

[Darth Humorous]

Hmmm...crickets.

[countryman]

Certain phones with electronic innards were polarity sensitive. Habe you tried reversing the line wires? Can you hear the DTMF Tones when you wire a second phone in parallel? The chip might be bad, but the keyboard is more likely to fail. I have successfully dismantled, cleaned and reassembled keyboards, but there is a risk to ruin them in the process.
Thanks for the good pics, the phone seems to have a conventional speaking circuit with electronic accessories. Good luck with getting it fixed!

[Darth Humorous]

Thank you for the reply. I tried reversing the wires as you suggested but there was no difference. I also hooked up a second, working phone in parallel and hear no DTMF tones when I press the keys from the offending phone. I do hear DTMF tones when I press the keys from the parallel, working phone.

I suppose it could be the keys, but everything looks so clean as if it had barely or never been used. I think the keys are of the conductive rubber pad type. Might there be some other component attached to the DTMF chip, like a resistor or capacitor that typically fails?

Mark