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Restoring WE 2500MM

Started by HarrySmith, July 03, 2014, 01:32:56 PM

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HarrySmith

I recently got a phone from a repeat cutomer for repair & cleaning. I thought it was a plain old 2500, the issue was touch tone not dialing. I assumed it was a polarity issue. I plugged in my test cord and it rang, sounded fine & had dial tone but would not break dial tone. I switched the line wires and Presto, it now dials. I was going to open it up and install a polarity guard. When I turned it over I see 2500MM 78272 stamped on it with a sticker for 2/79 refurb. There is a strange looking little network I have never seen before, the only marking I see is the same as the date stamp on the bottom, 78272. The dial is marked 35Y3D from 11/76 with a R 1/79 refurb date. I searched here and elsewhere and did not find much on this model. I did find a wiring diagram referenced here on the Porticus website. I figure this is made for a key system. The thread I found here was a member looking to get one working. He ended up spending a lot of time rewiring and ended up using a 2500DM diagram. He still ended up reversing the polarity to make it work. I was surprised to see no wires on the L2 terminal!? My question is can I just add my homemade polarity guard to it as is or rewire to a 2500 and add the polarity guard or what? My customer will be using it on a regular POTS line.
Harry Smith
ATCA 4434
TCI

"There is no try,
there is only
do or do not"

poplar1

#1
If you wish to add a polarity guard:  Move the white hook switch lead from C to the polarity guard input and the black dial lead from RR to the polarity guard input.  Connect the output of the polarity guard to (-) C and (+) RR.

(The inputs for a WE polarity guard are S for the white hook switch lead and T for the black dial lead. The outputs are  white (-) to C and green (+)to RR.)

The MM set uses one side of the hook switch (brown and yellow) for the A/A1 leads. This puts a short on the 2nd pair in the jack (black and yellow line cord). So you may want to move the brown hook switch wire from L1 to G if there is a second line on the wall jack, or a Princess transformer. Otherwise, you will short out the second pair in the jack unless you use a single pair mounting cord.

It also uses
Later 2500MM sets have a C4B ringer with only 2 leads. On these sets, for the incoming line,  tip is on F and ring is on A.

On older sets with a C4A (4-wire) ringer, tip is on 1 (on the terminal strip), along with the green Touch-Tone dial lead and the black ringer lead.  Ring is on 2 of the terminal strip, along with the green hookswitch lead and the red ringer wire. White hookswitch lead is on C. (BSP Section 502-582-400, Issue 1, January, 1970 in the TCI library
"C'est pas une restauration, c'est une rénovation."--François Martin.

rubey

I have a similar problem but suspect the touchtone keypad needs to be replaced.  Where would I go to order a replacement part?

Thanks from Seattle,
Ruben

Southernphoneman

Quote from: rubey on March 06, 2016, 11:25:30 AM
I have a similar problem but suspect the touchtone keypad needs to be replaced.  Where would I go to order a replacement part?

Thanks from Seattle,
Ruben
Ebay is your best bet, at varying prices, here is a link for one at a pretty good price, https://www.ebay.com/itm/301889048678

Ktownphoneco

Harry   ....   I have a schematic for the 2500MM printed in the Bell System Service Manual dated August 1980.    If you think it might be of help, let me know and I'll scan and post it for you.

Jeff Lamb

Babybearjs

Just a reminder.... the BSP's are always the first place to start when needing help... and the KSSM practice is the best place to find schematics for almost all the newer phones... I had this model once and was able to fix it with no problem.... Thank God for the KSSM! it may be a large file, but it had what I was looking for!
John

HarrySmith

Hi Jeff,
Yes, I will take that document. I have "fixed" that phone for the customer and he is happy with it. I disconnected everything and rewired it as a plain old 2500. Worked fine and was just what he wanted. I did end up putting a WE polarity guard in it also. I will keep the document for future use.  Thanks!
Harry Smith
ATCA 4434
TCI

"There is no try,
there is only
do or do not"

Ktownphoneco

Sounds good Harry.     Here's the schematic I mentioned earlier.     I scanned it at 600 dpi, and increased the scan size to 130% of the original in the manual, which will give you a nice print out on a standard letter sized 8.5" x 11" piece of paper.

Jeff

HarrySmith

Harry Smith
ATCA 4434
TCI

"There is no try,
there is only
do or do not"