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Old 3rd Dec 2020, 1:31 pm   #1
Sideband
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Default New BT phone won't work with old lead

Something for the phone buffs and hoping that someone can suggest what may be different.

Our old house phone (BT) has been playing up so time for a replacement. Now the old one is a typical cordless phone with a base station that includes answer machine etc and a digital display that shows the number of calls on the answerphone so nothing special. This phone has been working for about 10 years and is connected to a normal BT socket that includes a splitter and a broadband filter....filter to phone and the other outlet from the splitter feeds the router. No problems with any of that. Also more recently introduced is a call blocker that is simply in series with the phone. Again no problems with that.

So introduce the new phone, a BT model BT2700. Charged both handsets overnight and today tried to just plug it in place of the old. Now it comes with a BT lead ready to plug in to the BT socket but as it was rather shorter than the old one, I decided to use the old one so that was plugged into the base station (at this time the call blocker was not in the loop). Pick up the phone and press call....no dial tone. Odd I thought so I reconnected and rechecked the old phone ....dial tone OK. Tried again with the new base station and phone...simply plugged the old BT lead into the new base station....no dial tone. I then decided to try the new base station with the new lead which was shorter.....dial tone! So my question is why does the old lead not work with the new base station? Both are BT products and I would have thought that they would be wired the same. Could it be anything to do with the length of the lead? The old lead is about 1.5 metres longer....wouldn't have thought that would make any difference. Oddly enough there is a note in the user instruction that says only to use the lead supplied but I suppose that is a standard comment. I've used extensions in the past with no problems.

Anyone have an idea what the problem might be? Everything seems to work with the new shorter lead including the call blocker. Very odd (to me)!
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Old 3rd Dec 2020, 1:36 pm   #2
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Default Re: New BT phone won't work with old lead

I doubt cord length would make a difference. I don't think the connections at the phone ends of cords are standardised. Visual inspection of the two cords if the wire colours are visible, or continuity testing if they're not, would prove this one way or the other. Are all pins connected in both cords?
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Old 3rd Dec 2020, 1:43 pm   #3
cmjones01
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Default Re: New BT phone won't work with old lead

Leads commonly used with phones have an RJ11 plug on one end and a BT plug on the other. The problem is that most phones these days have the line connected to the middle two pins of the four, but the BT plug has it on the outer two pins. Therefore the lead has to rearrange the wires. This isn't always straightforward with the sort of flat cables that phones use: they lend themselves to straight-through connections, so there's often a little plastic lump behind one of the plugs that does the rearrangement.

There are some phones I've come across which use an RJ11 jack but with the line connected to the outer two pins, so a straight-through RJ11 to BT lead works. They tend to be older models intended purely for the UK market, in my experience, also having the ringer connected to one of the inner pins. No other country does it this way.

Summary: there are at least two ways of wiring a BT plug to an RJ11 jack, so it's not unusual for changing the cable to stop the phone working. Examine the wiring on the one that works closely and rewire the longer one to match. Chances are, if it's a new phone, it probably has the line on the middle two contacts.

Chris
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Old 3rd Dec 2020, 2:11 pm   #4
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Default Re: New BT phone won't work with old lead

I have a selection of BT to RJ11 leads and have found four different arrangements:

2 wires connected from 2 and 5 on BT to 3 and 4 on RJ11
4 wires connected as above plus 3 and 4 on BT to 2 and 5 on RJ11
2 wires connected from 2 and 5 on BT to 2 and 5 on RJ11
4 wires connected as above plus 3 and 4 on BT to 3 and 4 on RJ11

1 and 6 (the very outer pair on each plug) are unused.
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Old 3rd Dec 2020, 3:03 pm   #5
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Default Re: New BT phone won't work with old lead

Quote:
Originally Posted by cmjones01 View Post
Summary: there are at least two ways of wiring a BT plug to an RJ11 jack, so it's not unusual for changing the cable to stop the phone working. Examine the wiring on the one that works closely and rewire the longer one to match. Chances are, if it's a new phone, it probably has the line on the middle two contacts.

Chris
I think you might have cracked it! only the middle two contacts are used on the RJ11. I can only see two used on the BT plug as well

Phone wiring has always been a bit of a mystery to me...no idea what colour does what. I think there is a tool that allows you to rewire these plugs. I might just buy a modern extension to save faffing about, that's assuming a new extension is wired the same as the new phone.....

Why can't things be standard?
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Old 3rd Dec 2020, 3:24 pm   #6
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Default Re: New BT phone won't work with old lead

If you purchase a BT plug to BT socket extension, it will present the same four (or conceivably six) connections at the output as at the input, so is effectively simply moving the socket closer to the 'phone, and shouldn't introduce any wiring complications. You should then be able to use the new 'phone with its new cable.

The problem is not so much a lack of standards as too many conflicting ones!
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Old 3rd Dec 2020, 4:24 pm   #7
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Default Re: New BT phone won't work with old lead

I had that problem when trying to use a cordless phone that had come from my late brother-in-law's house in France. It turned out to be different connections in the RJ11 plug, which I wrongly assumed were standardised.
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Old 3rd Dec 2020, 4:52 pm   #8
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Default Re: New BT phone won't work with old lead

The first generations of phones with RJ plug did not always follow the standard of using the 2 center pins, pretty often the plugs are transparent, and the wires are colored so try to identify if it is differences between the 2 cables.
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Old 3rd Dec 2020, 6:21 pm   #9
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Default Re: New BT phone won't work with old lead

Quote:
Originally Posted by Dave Moll View Post
If you purchase a BT plug to BT socket extension, it will present the same four (or conceivably six) connections at the output as at the input, so is effectively simply moving the socket closer to the 'phone, and shouldn't introduce any wiring complications. You should then be able to use the new 'phone with its new cable.
The simplest answer of course...and you've just reminded me that I might have one somewhere....it's just remembering where!
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Old 3rd Dec 2020, 7:31 pm   #10
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Default Re: New BT phone won't work with old lead

Hi,
This is a common issue with a number of customers whom I deal with when at work.
What often happens is that folk purchase a new phone and, if the end where the wall socket is located isn't easily accessible, they use the existing phone lead from the RJ11 end for convenience generating a no dial tone fault.

The way I often describe it to them is that, if you hold four fingers out and imagine they are the phone end connections, on the (now seemingly more common) European standard the inner two connections are used for the phone line and on the "BT standard" the outer two connections are used.

I rarely, if ever, bother going in to details about two and three wire working where the third wire is used for ringing.

Regards

Andrew
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Old 3rd Dec 2020, 11:56 pm   #11
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Default Re: New BT phone won't work with old lead

Among other things, we make dispersed alarm units where I work, they use a similar RJ11 to BT line lead and in ours there are four wires, the centre pair in each plug crossing to the outer pins at the other end in each case.

We frequently get these units returned with the fault 'won't dial out' or 'not detecting BT line' only to find that the lead returned with the unit is from some other manufacturer's equipment. Rather than crawl behind the furniture to unplug the lead for the old equipment and plug our supplied lead in, they've noticed that the plug on the existing lead is the same and assumed that the wiring is the same and left it in place, then when it doesn't work they jump to the further conclusion that the new equipment (ours) must be faulty.

So no, not all of those leads are wired the same way.
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