WE 2500MM Polarity Guard

[novarlynx]

OK so I know it isn't a rotary phone but I can't think of a more better place to ask this question.

I have a Western Electric 2500MM and I have a WE polarity guard. What I am trying to do is install it in the phone so that it basically becomes a 2500MMG. I'm having trouble trying to figure out how to do it though. Here's the situation:

This phone has a type 35 touch tone dial, the older one with the big coils.

I looked at the wiring diagram for the 2500DM and 2500MM and noticed there are some differences, most obvious being how the phone is wired and the fact there is a wire missing from the hookswitch on the 2500MM that is present on the 2500DM.

I did find a wiring diagram for the 2500MMG but it shows a type 72 dial, which wires very different from the type 35, so that diagram was not helpful at all.

The wiring diagram for the 2500DMG shows a type 35 dial, and I tried to wire the polarity guard into the 2500MM like it said, but the MM's wiring just did not match the DM and so I gave up.

I know that these things can be installed because this phone actually did have the polarity guard when I got it, but I had to disassemble the phone and I did not draw a schematic assuming there was one available, and it turns out there isn't.


Can anyone help?

[poplar1]

To convert a 2500MM with 35-type dial to a 2500MMG:

Move the white hookswitch wire from C on the network to the S screw terminal on the polarity guard.

Move the black dial wire from RR on the network to T on the polarity guard.

Connect the white polarity guard wire to C.

Connect the green polarity guard wire to RR.

[poplar1]

The diagram for a 2500MM with 35-type dial is shown in Fig. 2, and Table B shows the wiring changes for installing a polarity guard. BSP Section 502-582-400 Issue 5, in the TCI library.

http://telephonecollectors.info/index.php/document-repository/doc_details/10006-502-582-400-i5

[Phonesrfun]

For the benefit of the group, what was the MM application for?

[poplar1]

1st  M designates that it is wired for A-lead control, to be used behind 1A1 or 1A2 key systems.
The second M means it is a "full modular" set.

On a D or DM set, both sides of the line are opened by the hookswitch.

The M or MM sets open only one side. Thus, the incoming line connects to F and L2, rather than L1 and L2.
This frees up one set of hookswitch contact springs that are then repurposed as A/A1 leads.

[novarlynx]

Oh interesting. So that explains why there is a warning on the bottom saying it is a business telephone and could cause a problem with the line.

On that note, if I found a hookswitch from a 500DM or 2500DM I could theoretically rewire this phone into a D model instead of an M model, right? The switch on this phone is missing one of the leads.

Could always just solder on a lead too...

[poplar1]

That "missing" slate (gray) lead isn't necessary for most applications. One of its uses was for use with a speakerphone, but that was usually with a 500S/500SM/2500S or 2500SM.

If you look at the diagram for a D/DM, you'll see that the yellow and slate hookswitch leads are normally closed while the phone is hung up. This really doesn't affect anything since both the yellow and slate lead are connected to L2 screw terminal.

[HarrySmith]

I once had a customer who I had done a few phones for bring me one of those and wanted it to work on his regular phone line. I used my Panasonic to test after refurbishing and it worked fine. I gave it back to him and next day he called to tell me it would not work. After several attempts I think I posted here and got the same responses, made to work as a business phone which explained why it worked on my PBX. I finally removed every wire and every component then started from scratch putting it back together as a regular old 500 C/D. After that it worked fine for him!

[poplar1]

Off-hook, there is no difference in the talking circuit between an M or MM set and a D or DM.
On hook, the only difference is that only one side of the line (L2 to C) is opened on an M or MM, and both sides are opened on a D or DM.

So either should work on a landline, or on a Panasonic. Not sure what kind of system your customer was using.

Still, it's usually a good idea to disable the A/A1 feature on a M or MM, if it's not going to be used with a 1A1 or 1A2 system. This can easily be done by moving the yellow (or slate-yellow) hookswitch lead from G to L1, so that both the yellow and brown hookswitch leads are on the same terminal, and the yellow   black wire from the 623D jack (or mounting cord) is alone on G. Otherwise, plugging the phone into a Panasonic 616 would short out the data pair (not good!), or plugging it into an RJ14 (2-line) jack would short out the 2nd line, or plugging it into a jack wired for a Princess with dial light would short out the 6-8 Volt Transformer.

[kka2446]

Hello Poplar 1, 
I just bought a bunch (22) black WE 2500mm sets that were used in a small office so reading your 2500MM thread couldn't have come at a better time... I'm going to 'restore' aka clean and they need it, polish etc.  My question, is it difficult to set 2500s up for single line residential basic service ?

If you can point me where to specifically look for info I'd really appreciate it. I'm guessing the TCI Service Docs BSP is the place, but where to look ??

Thanks in advance,
John
     

[poplar1]

Unless they were formerly used on an early Horizon Hybrid Key System, in which case the ringers are connectly differently, they should work as found on a residential line, so long as the polarity of the line is correct (green +, red -).

Still, unless you plan to use 2-conductor cords rather than 4-conductor, you may want to disable the A/A1 feature as discussed above.

[novarlynx]

Okay I'll rewire mine as a 2500DM and install the polarity guard then. Thanks everyone for the help!

[poplar1]

Okay I'll rewire mine as a 2500DM and install the polarity guard then. Thanks everyone for the help!

I don't understand why. We furnished the instructions for installing the polarity guard, and also the link to the diagram and table for a 2500MM with 35-type dial.

[poplar1]

Besides the missing slate hookswitch wire, and the number of conductors in the line jack, there is one other difference in a M or MM set compared to a D or DM set.

Notice that in the MM, the yellow and brown hookswitch wires are used for the A/A1 leads.
When converting a DM > MM, in order to use it with a key system, the incoming line and black ringer wire are moved to F, and the green and white hookswitch  are repurposed for A/A1.

Since the line must be interrupted before A/A1, in order to prevent a false holding condition, this means that the sequence that the various contact springs operate is not the same in the D/DM set as it is in the M/MM set. if one attempts to "wire a 2500MM like a 2500DM" -- i.e., using the same colors as in the other set -- the A/A1 will open first, if the yellow and brown are used.  In the M/MM set, the green and white must open before the yellow and brown when going on hook. In a D/DM set, the yellow and brown open first.

This really doesn't matter with a set used on a single line, without A/A1 supervision, but it seems a bad practice to try to make a set something it is not, rather than just make the minimum number of changes needed, if any.

It really is simpler just to install a polarity guard in the MM set, than to completely rewire a set as a DM.

[novarlynx]

Oh, ok. I was just concerned for a second since I have it hooked up to an ATA which dumps message waiting indicator onto the black and yellow pair. Did not want to damage that equipment. I'll just be sure to use a 2 conductor phone cord.

Thanks!