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!
On Friday, 3 April 2015 22:34:27 UTC+1, Part timer wrote:
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.
On 05/04/2015 20:42, firstname.lastname@example.org wrote:
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
On Sun, 05 Apr 2015 22:13:54 +0100, Part Timer wrote:
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.
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.
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