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Thanks Ed!
I really appreciate all the feedback I am getting here. You guys are great!
Mike.
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Joined: Dec 2007
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Retired Admin
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Retired Admin
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Now you know the mechanics behind DTMF: Dual- Tone Multi- Frequency ![[Linked Image from i754.photobucket.com]](https://i754.photobucket.com/albums/xx190/Professor_Shadow/Telecom%20pics/Untitled.jpg)
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Joined: Jul 2010
Posts: 61
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Originally posted by EV607797:
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. 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.
I'm a black & white type of guy.....the only grey in my life is the hair on my head!
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Joined: Dec 2010
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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
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Joined: Jan 2005
Posts: 15,383 Likes: 13
Moderator-Vertical, Vodavi, 1A2, Outside Wire
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Moderator-Vertical, Vodavi, 1A2, Outside Wire
Joined: Jan 2005
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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 Vaughn, MBSWWYPBX
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RIP Moderator-Mitel, Panasonic
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RIP Moderator-Mitel, Panasonic
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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! 
When I was young, I was Liberal. As I aged and wised up, I became Conservative. Now that I'm old, I have settled on Curmudgeon.
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Joined: Dec 2010
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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
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Joined: Jul 2001
Posts: 3,347 Likes: 10
Moderator-Avaya-Lucent, Antique Tele
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Moderator-Avaya-Lucent, Antique Tele
Joined: Jul 2001
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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.
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Joined: Jan 2012
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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.
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Joined: Sep 2006
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Did you notice the dates of the previous posts?
Arthur P. Bloom
"30 years of faithful service...15 years on hold"
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