Some phones ringing continuously - what is the fault?

[GMB]

We have several phones on our main landline of various vintages (although none are properly prehistoric). Just now, all of a sudden, some kind of line fault is causing some of the slightly modern phones to sound their ringers - continuously (not the ring-ring effect).
The very modern cordless ones do not see the problem.
If you pick up any handset the line is as expected and works and the others stop ringing.

It has been very wet for a while now and it looks like the fault is on the house wiring as the worst offending phone doesn't ring alone on the master socket.
So clearly some water is getting in - an annoying job to trace it.

But can anyone say what exactly some early electronic phones are using as the ring signal such that some cable leakage would make them ring all the time? (I thought the ring signal was a/c).

[McMurdo]

I suspect your older phones have their electronic ringer on the ring wire (3) especially if they rwere designed from the outset as an 'inphone' and rely on the bell capacitor to isolate it from the line voltage. Modern phones are usually engineered for pure 2-wire operation and the IC for the phone does the electronic ring voltage detection.
Certainly when we used to repair desk phones (!) the voltage from an AVO on ohms could make the phone ring softly sometimes.
Maybe you have a leak on your customer-side ring wire.

[JohnBHanson]

It could be a fult in the master socket - itis possible that the capacitor inside the socket that blocks the dc line voltage but allows the ac ring voltage through is defective. This could cause any phones that use the ring wire and have an electronic sounder to sound continuously.

As an alternative you could try plugging the problem phones into the socket on
an adsl converter and see if that fixes the problem.

[GMB]

Maybe you have a leak on your customer-side ring wire.

That seems to be the case, assuming the slave sockets have nothing but wiring in them.

The house wiring shows 15-22k of DC resistance between #2 and #3.
#5 to the others is 100-120k

I assume that infinity is the correct answer for all of these?
What would be the lower limit of acceptability?

(Now the nightmare begins - the house phone wiring was done by BT so is a bit of a mess, including the colour codes used)

[Dave Moll]

I wouldn't expect the resistance to no. 5 to be infinite if connected to the master socket, as there is usually a resistor between it and no. 3, though I don't think it's as as low as 120k.

[ricksteptoe]

We had exactly the same symptoms which several BT engineers seemed to think was water getting into a pole mount junction box, it also took out the broadband every time we got a call. After investigation it finally was traced to the capacitor in the master socket, replacement of the faceplate effected a full cure, only to be replaced about a month later by voip via fibre. One day I shall figure out how to wire a lead from the router to the house wiring so we are not stuck with just the cordless handsets supplied by BT.

Rick.

[McMurdo]

the resistor is 470K I think, BT call it a fancy name 'opt out of service resistor' which in english means unplugging your phones. Gives the exchange something to see in place of a ringing load during automated testing.

[Roger Ramjet]

I had similar when my better half spilled some tea into the line port of a Betacom caller display unit. The water allowed the the DC Line voltage onto terminal 3 connections & back fed down the house extension wiring to ring each phone's.

Another prime suspect - as John & Rick have suggested would be a leaky bell capacitor in the master socket. However this would only tend to ring phones with electronic ringers.

If phones with traditional AC bells are affected then the cause would most likely be on the serving phone line i.e. AC Voltage getting onto the [B Leg] of the incoming pair.

Rog

[ricksteptoe]

Re Roger's post, our system at the time comprised one four-way cordless and one 232 with bellbox, all were affected. I can only go by what the enginner told me.

Rick.

[Roger Ramjet]

Originally Posted by ricksteptoe

Re Roger's post, our system at the time comprised one four-way cordless and one 232 with bellbox, all were affected. I can only go by what the enginner told me.

Rick.

Yes.... the 232 would need definitely AC Ringing current which can only come from the serving exchange via a fault on the network cabling or water ingress to the DP at the top of the pole. Clearly tallies with what the BT engineer told you.

Rog