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Hi, I have an issue with "mating" a nonkey set (2702BM princess) with a separately mounted key 6041G. The BSP for the non-key set is 502-110-102 Fig 10, page 13 click here and the BSP for the separately mounted key is 512-210-103, Fig9, page 7 click here

I had no issue modifying the 2702BM set per the set modification table in the BSP nor do I have any issue with the separately-mounted key. I have 10 of the separately mounted keys working with various types of nonkey sets, and all work just fine. The issue is polarity, since the 2702 does not have a polarity guard and I get the unable-to-break-dialtone issue as when the polarity is reversed. I installed a polarity guard as found here: click but the modified 2702bm doesn't conform to the BSP for the polarity guard since it has a W and a BR lead moved from their normal terminals per the modification chart (W from F to L1 and BR from C to G). As an example, when I placed the polarity guard on the W lead at terminal T on the guard and then put the G lead on F and the BR on the S terminal on the guard and W lead on the guard to the C terminal, I got a short. By removing the guard, I had a dialtone on each of lines 1-5 but couldn't break the dialtone from the touch pad. I swapped ER and ET in the separately mounted key, and, strangely, I was able to break the dialtone and dial out on lines 2-4 but not on lines 1 and 5.

I also found another 2702BM which had a polarity guard installed by WECo, and it behaved exactly as the previously described 2702BM did when I installed a guard myself.

So, the questions are (2) if the 2702BM needs a polarity guard to break the dialtone, where should it be installed since it can't be installed in the normal way, and (2) why doesn't swapping ET and ER in the key (reversing the polarity of the tip and ring) affect only lines 2-4 and not lines 1 and 5 in the same set with the same connections to the separately mounted key.

Of course, this is just a hobby setup, so it isn't like I'm depending on this for livelihood, but I have messed around with this project until I can swap all this out in my head when I'm asleep!

Thanks to anyone who's brave enough to think this through.

Also, hopefully the links will appear on the forum as I embedded them; however, if not, the URL is in the text.

Bill Bentsen

Last edited by Telephonemaven; 11/02/18 08:55 PM.
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If it works on lines 2, 3, and 4, but not on 1 and 5, it sounds like you've got polarity problems going all the way back to your frame. Depends on how correct you want to be about it, I guess. If it were my setup, I'd start at the frame and make sure it was consistent there, then polarity guards would be irrelevant. I had a problem when I was setting up my system, as just described in another thread, where some of my sources of dial tone just came with the polarity backwards. Since they are all voip devices, and all have modular jacks, I could take the modular plug out of one and stick it in another and the polarity would be reversed. (Meaning I didn't have the wiring of the modular cords as a variable.) So where all the lines from these devices appear at my "CO block", I've straightened out the polarity there, so from there on through they are all correct. Just my 2 cents.

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The issue is now solved (almost), and it was the 2702BM set itself. I checked polarity within the 6041G separately mounted key, both with a DC voltmeter and a polarity tester (double kill), and each and every line was good. Still was a mystery why lines 2-4 were okay but lines 1 and 5 weren't with regard to polarity at the 2702BM set.

I took another 2702BM and modified it for 1A2 service in the same manner, and then cabled it into the separately mounted key, and it all worked fine. My goal was to have a beige non-key set with the corresponding beige 6041G separately mounted key with a 6-conductor beige cord. I could have swapped the covers and handsets between the two 2702BM sets, but it was easier to find a 702B in beige and use it, which is what I did.

The defective 2702BM is still a mystery. I've traced its wiring twice, but I didn't find any issues. Next step will be to unwire it and rewire it completely, testing all components along the way. No telling what happened to it during all the past years. I once had an issue with a multiline set with a headset jack, which didn't work properly. It took a complete rewire and continuity check on each lead to find the lead with a broken wire inside the vinyl. Maybe this one is destined for that, but on another day.

Thanks for all the help.

Bill Bentsen

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Just out of curiosity, does the new 2702 have a polarity guard in it? Maybe I'm reaching here, but this has my curiosity pegged. This is the kind of thing that would keep me up at night until I figured it out. I'm wondering if the key is alright. I'm assuming you checked polarity on all the incoming lines on the terminal board, and they were all ok, how about on the screws going to the 2702's mounting cord as each line key is pressed? I almost wonder if someone was having a bad day and messed up the wire wraps on the bottom of the terminal board. Seems unlikely, but with all this stuff pushing 40 years old, who knows who's been in there.

I am REALLY curious to what you find.

Last edited by ChrisRR; 11/03/18 06:39 PM. Reason: details
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Originally Posted by ChrisRR
Just out of curiosity, does the new 2702 have a polarity guard in it? Maybe I'm reaching here, but this has my curiosity pegged. This is the kind of thing that would keep me up at night until I figured it out.
When TouchTone telephones were invented, the very nature of them demanded that polarity be correct. If one of these vintage TouchTone phones were plugged into an incorrectly wired outlet, they were unable to dial out. You can receive calls and the phone will ring, but you cannot dial out. In the late 1970s they developed a device called a Polarity Guard and after that all phones incorporated this.

Sleep well.


BSP & Polarity Guards


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I know they're polarity sensitive, I have dozens of phones with polarity sensitive dials. Not one of them has a PG on it. One of the ways Bell took advantage of the dials being polarity sensitive was to reverse the polarity on a line that was using TT dialing when they weren't paying for it.

EDIT:

As a general rule, bell did NOT install PG's into normal service for this reason. There were some applications that required one to be installed, but it was uncommon. Towards the end of the bell system dials came with the PG built in, but from the 60's until the early 80's they didn't.

Last edited by ChrisRR; 11/03/18 09:38 PM.
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I think Milton was responding to whether NEW Princess phones have polarity guards installed.


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Originally Posted by ChrisRR
Just out of curiosity, does the new 2702 have a polarity guard in it?

No, neither of the 2702's have polarity guards. That's the first issue I referred to on my original post. When you use a nonkey set in a key system (a 2702 with a separately mounted key as I was doing), there is a chart which shows modifications required on the nonkey set. When you make these modifications, you can't place a polarity guard in the set because the required leads for the polarity guard have been moved around. The second try, which I didn't state, was with another 2702, which had a WECo installed PG, but which also had the same issues as set #1 with regard to not being able to use the PG because of the modifications for the key system.

I took a third 2702, which didn't have a PG, modified it according to the chart (all these references are shown on my original post), then tried it out on the key system, and it worked fine. Thus, something is in the #1 2702 which is causing these issues and neither the key system no any of the house wiring seem to be guilty. I haven't disassembled the set and rewired it to see why at this point.

I finally substituted a 702 (rotary princess) for the whole mess, and it works just fine.

Now, with regard to polarity on my existing wiring, none of the lines have polarity issues as proven by testing each line with a DC voltmeter and with a polarity tester: line #1, -42.4, line #2, -42.1, line #3, -44.1, line #4, -41.5. When I use the key system, I have a Melco V-136RT intercom on line #5, which draws -24.1. Each of the 5 lines show 'green' on a line polarity tester.

Each of these lines showed the same polarity and voltage all through the 636A key inside the 6041G separately mounted key when testing 1T/R, 2T/R, 3T/R, 4T/R and 5T/R. When testing ET and EH going to the 2702 set, each shows the same voltage when the corresponding line key is depressed.

The 2702 set shows the correct voltage as each sequential key is depressed. The problem, however, is the dialtone can't be broken on line 1 and 5. It can be broken on lines 2-4.

Line #1 dialtone is provided by Spectrum. There is not a polarity issue as above and shows proper voltage and checks out satisfactorily with a polarity tester. Lines 2-4 have the dialtone provided by MagicJack through 3 Xlink BTTN devices with ATA, all of which show proper voltage and pass the polarity checker. All also handle rotary dialing with no problem, although this is a TT issue. Line 5 is the intercom, which shows -24.1 volts and passes the polarity checker.

This setup has worked flawlessly for 5 years in this house and 15 years in my previous house, so I doubt issues in the wiring, especially since another similar phone (another 2702) works just fine as does a simple 2500 deskset.

Everything points to polarity, but I can't find the issue but it is localized to the particular set.

I have resolved the issue by using a 702B rotary princess with the separately mounted key. Interestingly, lines 1 and 5 were the issue on the key system, but line 5 was an ICM line. Line 1 was Spectrum and lines 2-4 were MagicJack with the ATA for rotary dialing. When I took the "problem" 2702 as a single-line set, then tested it line by line on the line 1 Spectrum and lines 2-4 MJ, it showed the same polarity issue (not breaking dialtone) on line 1 but not when tested individually on lines 2, 3 and 4. I couldn't check 5 since it was an ICM line on the key system. HOWEVER, when I used a similar 2500 set using the same method as above, none of the above issues occurred. I also used another 2702 without polarity guard, and none of the issues occurred. It's ONLY an issue with this weird 2702.

Other than unwiring and rewiring the 2702 to make sure there is no issue with someone messing with it over the years, I'm putting this to rest. It is interesting, but I've spent way too much time on it already!

Before I do that, I think I'll put a PG on this guy and perhaps just forget it all!

If you've read this far, you've spent way too much time on it, too! :o)

Thanks for your interest. You're a sick puppy just like I am!

Bill

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That's just weird...

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I'm sitting at my workbench soldering my Melco clones.... I have no room to talk..

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