Testing Telephones

[dencins]

Last night I was checking out some 302's and thought I would describe how I check transmitters, receivers and dials before connecting to the telephone network.

First this takes a computer with a sound card and a 3.5mm (1/8") patch cord.  I use my laptop since I can bring it to my workroom.  I cut one end of the patch cord off and attached it to a terminal block.  On the other side of the terminal block I attached a couple of leads to connect to the L1/L2 on the phone to be tested.

Plug the patch cord into the Headphone jack on the PC and you can test the receiver.  I play a song using Media Player and can hear it on the handset.

Then plug the patch cord into the Mic jack and you can test the transmitter.  I use Microsoft sound recorder to record what I say into the mouthpiece then play it back.

The next test is the pulse rate of the dial.  I use software called Zelscope (cost $20) to turn the PC into an oscilloscope.  The nice part of the software is it captures the screen so it can be printed.  I dial Operator and get the elapsed time.  Divide the elapsed time in to 10 and you get the PPS.  I have attached a picture of the screen of a WECo 2AB dial.

If all is okay I connect to the phone netwark and call myself to test the ringer.
 
Dennis

[Dan/Panther]

This is great stuff. Write it up in more detail or some photos.
D/p

[Phonesrfun]

Dennis:

That is great.  I need to look up Zelscope.

Looks like you can also guage the make/break ratio of the dial by looking at the relative on/off times.  What inputs do you use for Zelscope, the same sound card inputs?

[JorgeAmely]

Dennis:

I would reduce the gain a bit when checking the dial because I can see clipping of the waveform.

Are you biasing the line with some voltage before doing the dial scope shot? In a phone, there is about -5 to -9 volts present when dialing and the phone consumes some 20 to 30 mA when off hook.

[dencins]

Zelscope gets input from the sound card on all the tests I do and I use the same probe (more like poor man's probe).

I do not add any voltage  - just using what the sound card provides.

Most of the time I test dials off the phone.  I built a fixture from a "black box" that I attach the dial for testing.  I do not remember what jack I used on the sound card to test the dials (mic or line) but I will try it tonight.  Usually I test them after cleaning them so they are already off the phone.

You should be able to get the data needed for make/break but I have not tried to calculate it.  If I get PPS between 9 - 11 the dial will work on the network. 

I will let others play with reducing gain, etc.  I get what I need from the clipped picture.  I am not looking for absolute values - just the number of pulses over the time period.

I will get a picture of the "black box" but other than that there is not much to see.

I will look for the settings I use on Zelscope.  There is also freeware for PC Oscilloscope but Zelscope worked for me.

Dennis

[dencins]

Here are a few pictures of testing.  The first is the Black Box with the terminal block in the bottom.  I cut the end off a patch cable with a 3.5 mm plug on one end.  The red wire (tip) is connected to one screw and the ground to another.  The ground jacket gets very messy if you try to use it while testing.  I do not use the white wire (ring).  The hole in the cover of the box is to attach dials.

On the other side of the terminal box I attached two leads on the screws opposite the patch cable.  I use alligator clips to make it easier to connect to the phone.  The patch cable is plugged into Mic on the laptop and I run Sound Recorder.

In this case I was testing transmission.  The first test the clips are attached to L1/L2.  The voice was very weak.  To determine whether the problem was in the handset I moved the clips to the handset cord - one on the dial and the other on the coil.  This gave clear and strong results.  If it were still weak the problem would be the transmitter, handset or cord.  Since it was strong the problem is either the condenser, coil or wiring in the base.

Receiving is tested the same way but the patch cable is plugged into Headset on the PC and I play something on Media Player.  If clear and strong then no problem.  If weak I again isolate the handset from the base by clipping onto the black wire from the handset instead of the red.  I still clip onto the wihte wire from the handset.  If weak or no receiving then it is the receiver, handset or base.

I will go over dial testing in a separate post.

Dennis  

[dencins]

A correction - the Zelscope download is $9.95 not $20.00.

First I will cover testing a dial off the telephone.  The first picture shows the Black Box cover with a dial mounted to it.  The hole has been cut to fit WECo #2, #4, #5 and #6 as well as AE dials.  Note the two screws to connect the test leads.  Plug the Black Box into Mic.  When using Zelscope I have found the following:  

1. Change the buffer size. It is in the Settings on the top menu.  I increased to from 50 to 500 then click Save Settings in the drop down menu. This captures more than one second on the screen.

2. Increase MS/DIV from 1.000 to 200.000 to set x-axis to show 2 seconds.

3. I click the Start arrow button (upper left corner) then dial a number. I have the cursor sitting on the Pause button. When the dial stops, I click the Pause button. On the right side of the screen are Page Back and Page Forward buttons. I click the Page Back button one click and this usually gives me the full picture.

4. The program allows you to save data as Screen Shot (.bmp) which is usually 1.5M. I save it then bring it into another program to save it as .jpg (about 175K) to be able to email it. It also saves data as Text (bunches of data points) or Wave files.

When testing I dial Opeator for the test which gives me 10 pulses.  Zelscope lets you set to cursur points by left click and right click.  I set these at the two points I want to calculate elapsed time.  A pop-up box shows the delta.  Divide 10 by the elapsed time to get PPS.

To test a dial while still mounted on the telephone, connect the test leads to L1 and L2 just like testing transmitting and receiving.  The rest of the test is the same as above.

When I get a new phone I can connect the test leads to L1 and L2 and test transmit, receive and dial before connecting to the telephone network.