Touch-tone 35 type dial tuning/repair

[ma_xyz]

Hi

I've got a 35AH3D dial with frequencies off by > +5%. My small PBX does not accept the tones generated. I did "measure" the tones with an iPhone audio analyzer app and compare it to the output of a working DTMF phone. Pictures attached.

I would highly appreciate any suggestions regarding the best options to "tune" / repair the dial? Could it be related to the capacitor which looks burst? (the "outer" one, see picture attached) Should i try to manually tune the coils? (I do not have specialist equipment like an oscilloscope). Or should I try to get a type 72 dial to replace it? (wherefrom?).

The dial is from a "The Mickey Mouse Phone". This is my first and currently only US phone. I'm normally not interested in "Comic phones" or similar - but I think that Mickey is worthy of being on a Phone.  Another problem I have with it is that the ringer would not work - I'm assuming either because my Swiss/European PBX does not generate enough ring voltage or because of the ring frequency difference of US and European systems. Also here any suggestions welcome.

For the time being I fitted a Swiss button dial (from a Swiss "Modell 70" phone, the buttons are of nearly same size and use same distance, it is not a DTMF dial, it generates dial pulse) and a Swiss electronic bell (from a Swiss "Tritel Flims" phone). So I now have a kind of "Franken-Mickey" Phone. The dial is black instead of the original white but it looks not that bad. I also exchanged the white handset cord with a black one to match better. It works well and does not look to bad, still I would prefer to have it working with the original parts.

I did not expect this Phone to be such an interesting project - I allready read a lot about 4228 and other type networks, type 35 and type 72 tone dials, "design line" phones and western electric and the bell system in general. Might need to look for more US phones in the future - "real" phones not comic phones :-)

Attached a bunch of pictures.

Br
Michael

[ma_xyz]

And here also the pictures from the frequency "measurement"

Picture 6195 and 6196 are from the not working 35AH3D. All 7 frequencies are visible in the max. line lowest is ~736Hz (should be 697Hz) highest is ~1606Hz (should be 1477Hz).

Pictures 6197 and 6198 are from a working DTMF dial phone set.

[trainman]

That capacitor does look weird. Why not replace it and see what happens.

Those dials are tuned with variable coils. Newer dials has an oscilator chip.  A memeber of the collector community used to make a device used to tune those dials. Not sure if hes making them anymore. Used to sell in ebay. He called his device a Touchtone Pad Tuning Fork.  http://www.classicrotaryphones.com/forum/index.php?topic=16662.0

[ma_xyz]

thanks for the tips.

1. i will replace the capacitor as soon as i find a matching one (the 0.0442uF are apparently not a value still widely produced nowadays ...)

2. i will try to find plastic tuning tools matching the triangle shape in the coils ... i tried allready to move them with other tools but no success until now and am worried to brake something if applying to much force

currently no "tuning forks" on ebay .... I also assume that the kit would perhaps be a bit to expensive to only tune one pad ...

i also found this now: http://www.oldphoneshop.com/products/atc-touch-tone-dial-white-novelty-phone-7-lead.html

probably the easiest solution ...

[trainman]

You can combine capacitors in parrallel to acheive the desired value.

Yes, the replacement keypad is probably the best option. Then, you can experiment with the old one.

[tubaman]

A small difference like that should be tunable with the coils.
That 0.0442uF (44.2nF) cap sounds like a custom value. The nearest you'll get with standard parts is 2 x 22nF in parallel.