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1971 2500 D Troubleshooting

Started by GLadstone, July 27, 2018, 10:48:28 PM

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Hi Everyone,

I'd love your help troubleshooting another phone.

This one is a very clean and date matching Western Electric 1971 2500 D.

Components include:
-35Y3A dial (12 button touch tone)
-425 K network
-hard wired cords (with four prong plug at wall end of line cord)

Wiring Overview (as found / original)

Back side of the 35Y3A dial


We still have POTS landline service.


Lots of information to share, so I'll break this down into three separate posts:

1. First message / This post = Background and Symptoms
2. Reply #1: Troubleshooting Steps Taken to Date
3. Reply #2: General and Next Step Questions


Initial Symptoms:

As received, the phone had dial tone, but could not make or receive calls.

When pressing any of the touch tone dial buttons, the DTMF tones can be heard through the handset, but the DTMF tones sound "clunky" (versus "clear") and the dial tone continues after pressing a button.

Video clips comparing DTMF tones of this phone with a known working phone have been uploaded to YouTube:

This 1971 2500 D phone:
1971 2500 D Phone DTMF Tones- 6392

Known working touch tone phone:
Unisonic 6750 Phone DTMF Tones- 6388


1971 2500 D Desk Phone Videos (YouTube Playlist):


Current Symptoms:

I've made some wiring changes (detailed in reply #1 below), and the phone now rings and can receive calls, but still cannot make calls.

A video clip of this phone ringing after the wiring changes were made has been uploaded to YouTube:

1971 2500 D Phone Ringing- 6410

As with the Initial Symptoms:
When pressing any of the touch tone dial buttons, the DTMF tones can be heard through the handset, but the DTMF tones sound "clunky" (versus "clear") and the dial tone continues after pressing a button.


More details in reply #1 below.

Thank you for your time and consideration.

Take care,


Hi Everyone,

Thank you for your help!

Here is part two with the details of the steps taken to date:


Troubleshooting to Date:

Step 1:

The line cord at the plug end was repaired similar to what was detailed in the Line Cord / 505A Plug Questions for 702B Princess Phone topic:

Before line cord repair:

After line cord repair:


Step 2:

Traced the phone wiring per:

BSP section 502-523-401, Issue 8, May 1982 | Service: 2500D, 2500DM, and 2500DMG Telephone Sets Connections

Figure 1- 2500D (MD) Telephone Set, Connections (page 2)

Colored to match wiring as found:


Step 3:

Three changes were made to match the above referenced wiring diagram:

1. In the Four Prong / 505A Plug, the yellow conductor wire was moved from Y to GN.

2. On the 425 K Network, the black ringer wire was moved from K to G.

3. On the 425 K Network, the red dial wire was moved from G to T.

After making these changes, the phone now rings and can receive calls, but cannot make calls (dial tone continues after pressing any button).

Full wiring details are included below.



Wiring Overview (as found / original)

Line Cord (to Four Prong Plug)
Green --> G
Yellow --> Y (original / as found) --> G (current)
Red --> R

Line Cord (to 425 K Network)
Green --> L1
Yellow --> G
Red --> L2

Handset Cord (to 425 K Network)
Black --> B
Red --> T
White --> S
White --> R

35Y3A Dial (to 425 K Network)
Red - Green --> R
Orange - Black --> C
Blue - White --> S
Green --> F
Blue --> B
White --> GN
Red --> G (original / as found) --> T (current)
Black --> RR

Hook switch (to 425 K Network)
Green --> L1
Red --> S
White --> F
Brown --> C
Black --> R
Yellow --> L2
Slate --> L2

Ringer (to 425 K Network)
Red --> L2
Slate --> K
Black --> K (original / as found) --> G (current)
Slate - Red --> A

425 K Network Location --> Conductor Color --> Component
C --> orange - black --> dial
C --> brown --> hook switch
GN --> white --> dial
B --> black --> handset cord
B --> blue --> dial
R --> red - green --> dial
R --> white --> handset cord
R --> black --> hook switch

S --> white --> handset cord
S --> white --> dial
S --> red --> hook switch
T --> red --> handset cord
RR --> black --> dial
F --> green --> dial
F --> white --> hook switch

A --> slate - red --> ringer
K --> slate --> ringer
K --> black --> ringer ==> black ringer wire moved to G
L1 --> green --> line cord
L1 --> green --> hook switch
G --> red --> dial ==> red dial wire moved to T
G --> yellow --> line cord
L2 --> yellow --> hook switch
L2 --> slate --> hook switch
L2 --> red --> line cord
L2 --> red --> ringer


Step 4:

After making the above wiring changes, I searched through the CRPF archives and found this suggestion:

Quote from: Southernphoneman on May 02, 2016, 09:05:47 PM
It could be a polarity issue, try this test, change the red and green of the mount cord from the L1 and L2 respectively, then plug it in and if it dials out than you know thats what it is.

Reply #4 in the WE 2500DM won't break dial tone topic.

Switching the red and green line cord wires on the 425 K network resulted in a phone that could not receive or make calls.

The red and green line cord wires have since been changed back to their original locations.


To be continued in reply #2 below.

Thank you for taking the time to read through all this!

Take care,


Hi Everyone,

Here is part three with general and next step questions:


General Question:

Is this "clunky" DTMF tone sound part of the problem or is this the way it is supposed to sound on a 2500 D?

For reference, here is the link to the video clip at YouTube:

1971 2500 D Phone DTMF Tones- 6392

And, here is the direct link to the 1971 2500 D Desk Phone Videos YouTube Playlist:


Next Step Questions:

Do you think the problem is related to wiring connections, dial tone frequencies, or something else?

Searching through the TCI Library for related BSPs, I see that the 35-Type dials work at specific frequencies:

BSP section 501-164-115, Issue 10, May 1980 | 35-Type Station Dials: Identification and Maintenance

And, I've found a couple topics in the CRPF archives and online discussing analyzing and adjusting touch tone frequencies.

For example:

Touch-tone 35 type dial tuning/repair

Related blog post found searching for "35Y3A:"

Based on this information, I've been looking at the various "sound analyzer" android app options at the Google Play store, but I wanted to check-in with all you knowledgeable folks before continuing...

Is this this right path to head down next, or is there something else I should test first?


Thank you all again for taking the time to read through all this and sharing any and all suggestions you may have!

Take care,


You can check each of the 7 tones by pushing 2 adjacent buttons on the WE dial:
1 and 2 (or 2 and 3) will give the low tone common to that row.
Same with 4 and 5, then 7 and 8, then 0 and #

Then 1 and 4 will give the high tone common to the buttons in the first column, 2 and 5, 3 and 6.

It sounds to me that only the 4th low tone (common to *, 0, and #) is working.
"C'est pas une restauration, c'est une rénovation."--François Martin.


Agree with poplar1 - you only have one of the seven tones working, so you need to start looking at the keypad circuit.
I'm not familiar with how this is laid-out, but it could be something like a broken track or bad joint causing this.

Number, please!

I have had similar symptoms on a early model touch tone WE.  From memory: you can disassemble the touch pad and examine the contacts for each button.  A visual check may or may not tell you anything, but the real reason you are here is to CLEAN THE CONTACTS! 

Don't use the kitchen unless you are the boss in your home.  Take your cleaning project to the shop or garage.

I used very fine emery cloth folded over to have both sides working.  Cut or shape the strip to what size you want and slip the strip in between EACH set of contacts. Taking care so as NOT to bend the copper arm that holds the contact (that's the little triangle shaped point that you are trying to clean, at the end of the copper arm.)  Rub back and forth to get a clean contact point.  It does not take very much pressure and only a handful of strokes.

If you manage to bend one or more of the copper arms, you'll need to cuss and fuss the tension back into some semblance of OK.  Check for proper operation, pat yourself on the back, and then blow out the dust and residue.  No high pressure here, please.

I've had to do this every 3 or 4 years when the Princess TT was a daily user.


Be very careful with those contacts! Boy those things are touchy, you may be better off with contact spray cleaner, in that case do it out doors, and don't smoke!
I've tried working on those dials and they aren't easy to fix.
They are pretty much chuck and replace dials.
I've seen some in the dispatch dumpster before.


I'd be very surprised if this is a contact issue as all of the keys make an audible click when pressed (as per the YouTube video).
I'd be focusing on circuit issues.


Well I agree, but I have had a couple where the switches have been dirty enough to keep the dial from working properly.
And it was quite difficult to clean them without screwing up the gap in those switches, and don't forget there is a small pileup on the back of the dial. Those may not have anything to do with the tones.
I wish you luck, I think you're going to need it.


Hi poplar1, tubaman, Number, please!, and Key2871,

Thank you for all the great suggestions and tips!


A couple quick updates and notes:



To get a better sense of the touch tone keypad tones, I've installed a couple different "sound analyzer" android apps (links below) and have been getting familiar with them while running a couple quick tests with an online DTMF tone generator (link below) and the known working touch tone phone (the Unisonic 6750).

So far, the apps are working better than I expected.

Next, I'll continue testing these apps, try to get baseline frequency readings, and then take a closer look at the dial.



In case anyone is having similar issues, here are a few links and resources:

"Sound Analyzer" Android Apps from Google Play Store:

Advanced Spectrum Analyzer PRO (last updated 2017):

Spectrum Analyzer (last updated 2014):


Online DTMF Tone Generator:


KS19355 L3 Touch Tone Adjuster Tool Photo and Specifications:

OLD Wanted: KS-19355 Adjuster
In the first post, Dave F shares a photo of the tool.
In reply #13, Teleplay shares a photo of the tool specifications.

Related BSPs:

074-202-121 Tools - Adjusters IV - Description (June 1979)

074-202-121 I3 (January 1982)

Take care,


Hi Everyone,

Good news to report:
The 35Y3A (12 button) touch tone dial has been repaired and calibrated.

And, this 2500 D phone now works as expected (rings, receives calls, and makes calls).


Long story short, I ended up sending the dial to Steve Hilsz.


Thank you all for your help and pointing me in the right direction!


For those of you troubleshooting a similar problem and/or interested in further details, I'll share them in the next two posts:

1. Reply #11: Troubleshooting Continued (Before Sending to Steve)
2. Reply #12: Additional Resources and Quotes From Topics of Interest


If you prefer to view things in multiple tabs or windows, this information is posted to my phone project notes website here:

And, here is the direct link to the 1971 2500 D Desk Phone Videos YouTube Playlist:


If you are having a similar problem with your touch tone dial, and prefer to just send it to Steve, here is his website:

And, here is a related topic in the CRPF Vendor Experiences section:
Steve Hilsz, dial repair


To be continued in reply #11.

Take care,


Hi Everyone,

Here is part one with the troubleshooting steps taken before sending the dial off to Steve Hilsz.

(The numbering is continued from reply #1 above.)


A note about the "Sound Analyzer" app used:

While testing a couple different "Sound Analyzer" apps, I was also experiencing some issues with my cell phone and factory reset it.

At the time, I had spent more time exploring one app more than another, so I chose to just reinstall and use the following app:

Advanced Spectrum Analyzer PRO (last updated 2017):

This app was used with the default settings and I found it gave consistent readings with my device.


Step 5:

Baseline DTMF Tone frequency readings were taken and compared with a known working touch tone phone and an online DTMF tone generator.

Video clip at YouTube:

1971 2500 D Phone DTMF Tones- Frequencies (As Found)- 6478

Chart of Baseline DTMF Tones:

(For comparison, see the chart included in Step 8 below.)


Step 6:

Checking the dial contacts and switches.

All switches and contacts appeared normal, except the top switch (column 2 buttons: 2, 5, 8, 0):

The metal contacts on the top switch were found to be twisted and did not lie flat against the plastic when no button was pushed.

After flattening these contacts, all rows had DTMF tones, but the columns did not.

Top Switch (as found):

Top Switch (after flattening contacts):

Video clips at YouTube:

1971 2500 D Phone DTMF Tones (After Top Switch Adjusted)- 6530

1971 2500 D Phone DTMF Tones- Frequencies (After Top Switch Adjusted)- 6534

DTMF Tones of this step are included in the chart in Step 8 below.


Step 7:

Cleaning the dial contacts and switches.

Searching through the CRPF archives, I found consistent reports that a dial with a single DTMF tone often has a switch issue and the general advice is to gently clean the contacts with card stock paper, a business card, or bond paper.

For example:
Western Electric 2554 issues., reply #10

For ease of reference, this is message is quoted below in reply #12.

In this case, the dial was cleaned with:
-A "Rocket Air Blower" (to clean the loose dust and dirt).
-A textured piece of card stock paper (to gently clean the contacts).

While cleaning the dial contacts, I noticed that the right coil cover (as seen from the back of the dial) was loose.

And, when testing the DTMF tone frequencies after cleaning, the DTMF tones were worse than before.

Coil Covers (as found):

Coil Covers (after cleaning contacts):

Note that the right coil cover has been rotated from its original position.

Video clips at YouTube:

1971 2500 D Phone DTMF Tones (After Contacts Cleaned)- 6583

1971 2500 D Phone DTMF Tones- Frequencies (After Contacts Cleaned)- 6577 

DTMF Tones of this step are included in the chart in Step 8 below.


Since the dial DTMF tones were getting worse instead of better, I contacted Steve Hilsz.

For those of you interested in continuing DIY repairs at this step, you may find the following topic helpful:
1500D 10-button key pad problem - loose oscillator coil cover fix

For ease of reference, this is message is quoted below in reply #12.


Step 8:

Send the dial to Steve to repair and calibrate.

Steve noted that both ferrite coil covers were loose.

He got them back in place, glued, and calibrated the dial.

With Steve's help, the phone is now able to make calls and works as expected.

Video clips at YouTube:

1971 2500 D Phone DTMF Tones (After Repair and Calibration)- 6628

1971 2500 D Phone DTMF Tones- Frequencies (After Repair and Calibration)- 6624

Chart of DTMF Tones (Steps 6 - 8 ):


To be continued in reply #12.

Take care,


Hi Everyone,

In case anyone else is considering a similar repair, here is part two with an additional resource and a quotes from a couple topics of interest:



DTMF Tone Frequencies and photos of Western Electric Type 35 touch tone dial (including the dial switches and contacts):


Topics of Interest:

Troubleshooting and Cleaning Tips:

Western Electric 2554 issues., reply #10

Quote from: Phonesrfun on February 09, 2016, 01:00:56 AM
Before the introduction of the IC chip to make touch tone tones, the dial operated with switches and tuned circuits with induction coils that would occasionally fall out of tune.

If the dial is only producing a single tone, as opposed to two simultaneous tones, then it is probably a switch issue.  There are many switches on the early touch tone dials.

If it is producing two distinct simultaneous tones, then it might be a tuning issue.  If that is the case, I would send it to Steve Hilsz for a tune-up.  In order to tune a dial, you need a certain sized triangular non-ferrous tuning tool and a frequency counter, and some patience and knowledge of the dual tones produced by each button.

If it is a switch, then cleaning the switch contacts with a piece of card stock rubbed between the contacts should work in most cases.  You don't want to use anything more abrasive than say a rough piece of card stock, such as a business card.  Otherwise the precious metal points on the switch contacts will be worn off and you will be forever trying to keep the switch contact working from that point on.

If you prefer more detailed step by step instructions, check out this post by Victor Laszlo in this topic:
Need some help with Modular Plug and Touch Tone Key Pad, reply #17


Fixing loose oscillator coil covers:

1500D 10-button key pad problem - loose oscillator coil cover fix

Quote from: Tim Mc on June 13, 2014, 11:18:41 AM
I received my 1500D yesterday and hooked it up to the house line to test.  The DTMF tones sounded off and would not break dial tone.  I removed the shell and the keypad's clear thin plastic dust cover, and burnished any contacts I could reach with a piece of paper index card.  I still had the weird tone problem, so I removed the bottom half of the dust cover.  One of the round ferrite pot covers (oscillator coil?) with its center coil was loose and dropped out.  I tinkered with it and found that I could change the tone by rotating the coil cover while holding it firmly in place.  I experimented until the tones sounded right and could break dial tone.  A dab of CA adhesive (super glue) and it's now in working order. 

Anyone that has a 1500 key pad experiencing weird tones may want to see if the coil covers are loose.  Hopefully this will save a key pad or two from the trash bin in the future.


Good luck troubleshooting and repairing your touch tone dials-- I hope this helps you return your phone to working service!

Take care,