Strange landline behaviour

[Part Timer]

Got a plain Tesco phone which started a strange behaviour which I'm wondering if anyone else has experienced before. It started ringing with a continuous (i.e. no spaces between rings) whilst on-hook - my mum thought a neighbour's car alarm had gone off! If the handset is lifted, it functions as normally. If one of the other phones has its handset lifted, the ringing on the faulty phone stops (until the other phone's handset is back on-hook). It's a 2 wire cable to the wall, so has its own "master socket" ring generation circuitry. That plugs in underneath and appears as the red and green wires in the middle on this pic:

Or full size The handset plugs into the side of the base (Jamaican flag coloured wires). No obvious dry joints on the board. Would it be the large red capacitor or the large carbon film resistor at fault? If it's a 20p fix I'll do it, otherwise the bin beckons!

[spuorgelgoog]

This sounds consistent with the ringing capacitor failing short-circuit and passing DC to the ringing circuit; many electronic ringers will ring on DC.

When any handset is off-hook the DC line voltage falls to below a level which triggers the ringer.

If desoldering/opening one leg of the large red cap resolves the problem that's probably the cause; replace with a non-polarised capacitor of similar value or 2.2 uF if you don't know the value.

Owain

[Part Timer]

Thanks for that! The red capacitor says CSD MER 105J250V - is it 1uF?

[Brian Gaff]

Yes I've had this happen way back but in them days it looked a bit like a large sweet with wires and coloured stripes. It got moissture in it where the wires entered I think. brian

[Brian Gaff]

Have you had any lightening near you recently? That can also upset these caps.

Brian

[meow2222]

NT

[Dave Liquorice]

ringing

Or a A B wire swap between sockets. Check that every socket is wired pin 1 to pin 1, pin 2 to 2 etc.

[spuorgelgoog]

In some circumstances, but not usually on a 2-wire phone.

Owain

[Part Timer]

Dave, nothing else had changed when the cheap Tesco phone went on the blink. I've done as Owain suggested in an earlier post and desoldered the offending capacitor which cured the ringing problem when the phone was plugged back in to test. It will be shelved pending obtaining replacement cap.

James

[Dave Liquorice]

I don't think we know if it is a two wire phone? Though most are these days, unless it can pulse dial in which case it must pick up the "bell wire" to supress bell tinkle when pulse dialling.

Didn't start to use a socket that wasn't being used before or shuffle phones about when this new one arived?

The capacitor is the network side of the demarcation point between the network and your responsibilty. The test socket behind the lower removeable plate of the NTE ("master socket") is the actual point. Extension sockets your side of the demarcation point shouldn't have the capacitor, resistor or spark gap.

[spuorgelgoog]

I think given by the information provided by the OP, including photographs, we have established that it is.

Owain

[Part Timer]

Nothing had changed for at least 6 months to a year, one day my mum had heard this one phone go kaput as per my original post. She just happened to mention it while I was visiting over Easter.

Understood. None of the extensions do (only one master socket downstairs, not tampered with on this visit!) It's older than an NTE5 but that's not relevant here. My original post related to the capacitor (found to be duff) and resistor in the faulty two wire Tesco phone which I suppose are to help the thing in ringing/not ringing as required. Thanks anyway - I value all replies and know you have expertise in this. Peter Parry's excellent site

taught me much in 2001 when I first did some troubleshooting and extensions, spurred on by an AS physics textbook briefly mentioning the

2 and 3 wires, R, C and spark gap.

[Part Timer]

Phone is now fixed and back together. Long live uk.d-i-y and all the advice people give so willingly.