Western Electric 302--- dial tone issues

[Ken Weitzel]

Adam-

The responses to your question appear to contain all the information you
need to find the source of your problem, but scattered among them!

Basically, the phone presents a relatively low resistance across the phone
line when the hook-switch closes. Reacting to the resulting current, a
current-sensing relay at the central office closes, and a dial tone is
sent back down the line.

The telephone's dial is also connected across the phone line. When you
dial, a short circuit is intermittently connected across the line to
generate a number of higher-current pulses corresponding to the number
dialed. In your case, the current caused by dialing activates the
current-sensing relay, which had NOT been previously activated by the hook
switch.

Using an Ohmmeter in conjunction with the diagram, you should be able to
troubleshoot the problem. As someone mentioned, you must disconnect the
phone first, because the 48 Volts DC from the phone company might damage
your meter!

Someone mentioned a third wire that had to be connected to get a phone to
work. Modern telephones use two wires to connect to the phone company,
but early phones had a third wire used for party lines. In addition to
using different ringing frequencies to signal individual parties on the
line, the phone company also could apply the ringing voltage from one side
of the line to ground, the other side of the line to ground, as well as
line-to-line as is done today. If such a third wire were not connected,
the ringer would not work but calls could be made.

Fred

Hi Fred...

Respectfully suggest that dialing momentarily pulses the line open,
as opposed to "more shorted"

Take care.

Ken

 

[Fred McKenzie]

Good discussion, but one small correction: When you dial, the dial contacts
open the current path and then close the path for each pulse. During the
time that set of contacts is open, another set is closed, shorting out the
earpiece so there is no click in the ear. The CO reads each pulsed
open-interval. When the string of (one to ten) open pulses completes, the
current path is simply maintained by the closed dial contacts.

Don-

I stand corrected, as Ken also noted.

From your explanation, it would seem that Adam should look for an open
earphone connection as one possible cause of his symptoms.

Fred

 

[Ken Weitzel]

Don-

I stand corrected, as Ken also noted.

From your explanation, it would seem that Adam should look for an open
earphone connection as one possible cause of his symptoms.

Hi...

Went out to the shed, searched around a bit, and came up with an old
rotary dial phone.

Not nearly as old as we're looking for (plastic, maybe the '60's?), but
perhaps better than nothing. If the OP would like I'll be happy to take
it apart a make up a bit of a schematic for it. Might be helpful.

Take care.

Ken

 

[Michael Black]

Hi...

Went out to the shed, searched around a bit, and came up with an old
rotary dial phone.

Not nearly as old as we're looking for (plastic, maybe the '60's?), but
perhaps better than nothing. If the OP would like I'll be happy to take
it apart a make up a bit of a schematic for it. Might be helpful.

Did they really change much, after the obvious point where dials were
introduced? One reason they were always reliable was that they were
so simple, and there's little reason to change that until the time
when electronics started being added.

Michael

 

[Ken Weitzel]

Did they really change much, after the obvious point where dials were
introduced? One reason they were always reliable was that they were
so simple, and there's little reason to change that until the time
when electronics started being added.

Michael

Hi...

Dunno, sure are lighter though

Plugged this one in, rang it. What a flashback hearing a real
mechanical bell again

Take care.

Ken

 

[Ross Herbert]

Hi all!

This might be a long shot... but here goes.

I have an old, 1941 Western Electric Model 302 Telephone. This is a
'real' phone, and has always continued to work flawlessly... until....

We took the phone apart to clean and polish the case, and install new
cords. I had to remove the dial and the hookswitch. New cords (cloth
wrapped of course!) were installed and everything was put back together
exactly as it was.

We have a wiring diagram for it, everything is in the correct place.
Here are its symptoms:
1. When listening with the phone off the hook, you can hear the line
noise, but no dial tone
2. slight motion of the pulse dial gives a momentary dialtone, which
then disappears
3. the phone rings properly, but will not answer when lifted off the hook.

The wiring diagram from Western Electric indicates that one of the two
clapper switches in the hook switch assembly "makes last" but it does
not give any specifications-- should there be a delay between the
closure of one part and then the other? I can't really imagine the phone
company in 1941 detecting an 80ms delay between two switches?

I've really been at wits end because nothing seems to have changed
except that the phone wont trigger a dial tone. My previous
understanding was that the CO (central office) detected a closed circuit
through the hook switch and that was what triggered the dial tone. I've
checked all contacts in both the hook switch and dial and they all
connect and disconnect cleanly.

Any suggestions, interest, or help would be grately appreciated!

Thanks again!
-Adam
[email protected]

Without a circuit I can only guess...

You gave a clue in that dial tone is momentarily audible when the dial
is moved. Could it be that in your refurbishment you have altered the
spring tension on the dial loop interrupter contact?

Since the off-hook line loop condition relies upon current through
this contact it may not be making firm contact when in its normal
position. Also check that the other off-normal springs are also making
firm contact when the dial is rotated from its normal at home
position. Clean and re-adjust spring tension where necessary.

Ross Herbert

 

[Ross Herbert]

While this page http://www.dmine.com/phworld/pictures/weco/ doesn't
have a circuit of the WE302 the pictures appear to show 5 wires
connecting to the dial.

Here is a circuit of a Kellogg phone of a similar era which is fairly
typical of telephones used in the USA, UK and Australia
http://web.ukonline.co.uk/freshwater/aus/1040.htm Note that the W,X, Y
and Z springs are all part of the dial mechanism and while the Kellogg
shows 6 wires to the dial springs this is because Kellogg routed the
bell circuit through the W contact on the dial. In most cases
manufacturers didn't do this so the dial connection can be made with 5
wires as shown in this APO 332AT telephone from the same era.
http://web.ukonline.co.uk/freshwater/aus/diags/332at.jpg

I suspect that the WE302 will be similar to the latter circuit.

 

[Adam]

Just wanted to thank everyone for all the suggestions!

I'm going to attempt another look at it this afternoon, I'll try to post
a follow-up if I can get anything else working.

Thanks again everyone,
Adam



Adam sent the following message on 10/11/2005 1:52 PM:

 

[Bob Shuman]

Yes, out of circuit resistance measurements across the line inputs in both
on and off hook would be very useful. I also had suggested he verify the T
and R were not wired in reverse since that too would give the very same
symptoms (allow the phone to ring, but not go off hook properly). I've seen
no reply to that suggestion either.

As someone else has already said, it seems he has received a good deal of
advice and suggestions ...

Bob

 

[Bill Janssen]

Ken Weitzel ([email protected]) writes:


Did they really change much, after the obvious point where dials were
introduced? One reason they were always reliable was that they were
so simple, and there's little reason to change that until the time
when electronics started being added.

Michael

I think the 500 set had some varistors to regulate the volume out of the
mic. (transmitter).
The intent was to make all telephones the same volume when the signal
reached the Central Office.

Bill K7NOM

 

[Adam]

Many thanks for all of the advice! Now for the explanation of what went
wrong, how I found it.... and hopefully you guys won't take away my
engineering degree!

Using a wiring diagram from the web and my ohmmeter, I again reassured
myself that it was wired properly. The two switches in the hook switch
and three in the pulse generator all made and broke contact cleanly
(also verified with my meter).

Then what to do?! Having a small stockpile of 500 series phones
available, I pulled a handset off and connected it. This turns out was
from a newer generation 502... but we got a dial tone! It was much much
too quiet though-- which I surmise was from the speaker impedance not
matching the transformer. Finding an older 502 & connecting the handset,
IT WORKED!

Meanwhile as background, we had carefully cleaned the contacts on the
mic and speaker cartridges for the 302. I had checked the resistance of
the cartridges out-of-circuit so I knew they weren't blown. And I had
checked the wires on the phone end IN-circuit. Bad Idea. Seems I was
seeing the resistance across the transformer not the resitance across
the mic. The simple answer--- if you disconnect the microphone
cartridge, you get the same symptoms and all that was wrong was the
cartridge wasn't making clean contact with the spring contacts. Cleaning
them up and bending them out a little, it worked fine.

Thanks so much for all the suggestions, they did help us narrow down the
search and locate the problem.

Slightly embarrased,
Adam (who's usually fixing other's problems by telling them they needed
to plug it in-- seems I should take my own advice!)

 

[Bob Shuman]

Thanks for sharing what you found. Glad you got it working. It should last
another 65 years now since it is a genuine WE Bell System phone.

Bob

Many thanks for all of the advice! Now for the explanation of what went
wrong, how I found it.... and hopefully you guys won't take away my
engineering degree!

Story deleted

 

[Adam]

Thanks Bob!

And now with the advent of google archives, someone 65 years from now
will go to figure out why they can only get a momentary dial tone, and
find this thread and polish their silver!

Adam



Bob Shuman sent the following message on 10/16/2005 7:43 PM: