746 will no longer ring! - UK Vintage Radio Repair and Restoration Discussion Forum

chipp1968 · 26th Jun 2016, 11:22 pm

I purchased this phone Saturday as a present for a neighbour.

It I think is a 1970 model modernised by BT in 1982, with I assume a new circuit board bell set etc .

It was already converted and from what I can see all is correct. It has 2000 ohm coils so I assume does not need the resistor conversion.

I plugged it in Saturday and left it in circuit until this evening. As far as I am aware yesterday it rang perfectly ok.

I have been out all day but noticed this eve it doesn't ring any more.

I cant see anything wrong. There is continuity if I use an analogue meter between T4 and T16. I tested the line cord and that corresponds with the plug to terminal ends ok

I forgot to say when I opened up the phone the wire from the bell to terminal 16 was hanging and the screw missing. I pinched it from T9 and reinstated, But it doesn't work.

TonyDuell · 27th Jun 2016, 6:24 am

Do you know _for certain_ that it ever rang correctly when plugged into that socket in your house?

I am wondering if there is a problem with the 'bell shunt wire' going to pin 3 of that socket. Or with the ringing capacitor in the master socket. I've heard that the bell shunt wire can cause problems with ADSL so it is sometimes not connected. Modern telephones often contain their own ringing capacitor and just need the wires on pins 2 and 5.

chipp1968 · 27th Jun 2016, 7:47 am

I believe it did..
But there was another Bakelite phone plugged in at the same time that rang as well so bell phones are working already on the line .

How do I test for what you suggest ?

chipp1968 · 27th Jun 2016, 8:42 am

Well .It now is working..at least in the main socket .
It didn't last night .

The main socket is in the bedroom . In the extension downstairs it still doesn't ring .

Maybe it waste of those double faults ..the wire being loose , yet Im sure it originally did ring down here .

I shall take it to neighbours later and see if it works ok there . What could be the wiring problem for it not to work down stairs ?

Nickthedentist · 27th Jun 2016, 9:30 am

Hi Paul, nice to see you back here. The red Hacker is still going well...

Quote:

Originally Posted by chipp1968

What could be the wiring problem for it not to work down stairs ?

Are you using plug-in broadband microfilters? You need to use a top-quality one for these old phones to ring.

Nick

mike_newcomb · 27th Jun 2016, 10:59 am

Hi Paul, if the phone works in the master socket, but not in a slave, I would suspect pin 3 is not connected somewhere.
Generally 3 to 3 is connected from the master socket onwards, and used for ringing by older phones.
By convention 4 to 4 is also connected, although in theory 4 is not used.
I had the same problem and was tearing my hair out trying resolve.
Eventually I traced th cause to a broadband filter actually missing pins 3 and 4, which I have never seen again, but since as a matter of course check the filters.

Regards - Mike

chipp1968 · 27th Jun 2016, 1:43 pm

Glad the Hackers good Nick.
My main socket has a built in filter ,so I dont think I need any more ?
Possibly part of the extension isn't working or wired correctly .
I took it to neighbours with no time to test for ring ..But I noted that there was some interference pick up on the line which I didn't get at home .Thats probably because of no filter ?

Nickthedentist · 27th Jun 2016, 2:37 pm

Yes, and yes.

If it works in the main, filtered socket, the phone is fine, and its your extensionwiring that's been pared-down from 3 to 2 wires; this improves broadband speed but means old phones won't ring.

The solution is to use a plug-in microfilter at your neighbours or for your extensions.

N.

Dave Moll · 27th Jun 2016, 3:24 pm

Just to expand on what Nick says: the use of the microfilter in this instance is not to filter out the broadband (given that you say this is done in your master socket), but because it normally contains its own ring capacitor, therefore putting out the ring current on pin 3.

TonyDuell · 27th Jun 2016, 3:31 pm

I've not tried this, but it should work.... Let me know if I am right.

You should be able to use the ringing capacitor in the 746, which is conneted between T9 and T7. Try :

Leave the 3k3 resistor (if you are using one with an old 1k bell) between T4 and T5, if a 4k bell, then leave the strap between T4 and T5.

Disconnect the blue wire of the line cord from T6 and 'park' it on a spare terminal, like T14.

Strap T6 to T7. (T6 should also be strapped to T5 as before).

Strap T8 to T9, and have the red wire of the line cord on there

Leave T16-T17-T18-T19 strapped and to the white wire of the line cord.

chipp1968 · 28th Jun 2016, 7:50 am

Thank you Tony .A good option to try .
Its now at its new home , but they haven't tried it yet for some reason ,so I wont persist until I know it works there or not.

Oldcodger · 28th Jun 2016, 4:45 pm

Something to remember. Many years ago ( feels like centuries now), I was in the process of fitting an extension ( PL1A) to a house. All went well, and at the final test, the main phone ( 700 type) failed to ring. Mad panic- N diagrams out and everything OK. Meter across bell coil showed ringing in ,but bell didn't ring. I made a quick call to the maintenance bloke, who told me that this place had complained several times that the main phone didn't ring at times. Several NFF reports for this one. New phone fitted and problems resolved- it was suggested that phone had polarised bell coil.

russell_w_b · 29th Jun 2016, 10:55 am

Depolarised, may be, but this takes quite a bit of energy to do: typically 5 Amps round forty turns wound into the bar magnet of a 59A bell-movement will demagnetise it sufficiently as to render it inoprative.

Less than an Amp in the opposite direction will make it work again. A bell won't normally have d.c. Passing through it to depolarise it in any case.

Muck in the armature, maybe?

chipp1968 · 29th Jun 2016, 8:55 pm

Well they have tested it and it is working ok in its new home ,so Thanks everyone .

26th Jun 2016, 11:22 pm	#1
chipp1968 Rest in Peace Join Date: Jul 2006 Location: Somerset, UK. Posts: 2,356	746 will no longer ring! I purchased this phone Saturday as a present for a neighbour. It I think is a 1970 model modernised by BT in 1982, with I assume a new circuit board bell set etc . It was already converted and from what I can see all is correct. It has 2000 ohm coils so I assume does not need the resistor conversion. I plugged it in Saturday and left it in circuit until this evening. As far as I am aware yesterday it rang perfectly ok. I have been out all day but noticed this eve it doesn't ring any more. I cant see anything wrong. There is continuity if I use an analogue meter between T4 and T16. I tested the line cord and that corresponds with the plug to terminal ends ok I forgot to say when I opened up the phone the wire from the bell to terminal 16 was hanging and the screw missing. I pinched it from T9 and reinstated, But it doesn't work. Attached Thumbnails

27th Jun 2016, 6:24 am	#2
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,225	Re: 746 will no longer ring! Do you know _for certain_ that it ever rang correctly when plugged into that socket in your house? I am wondering if there is a problem with the 'bell shunt wire' going to pin 3 of that socket. Or with the ringing capacitor in the master socket. I've heard that the bell shunt wire can cause problems with ADSL so it is sometimes not connected. Modern telephones often contain their own ringing capacitor and just need the wires on pins 2 and 5.

27th Jun 2016, 7:47 am	#3
chipp1968 Rest in Peace Join Date: Jul 2006 Location: Somerset, UK. Posts: 2,356	Re: 746 will no longer ring! I believe it did.. But there was another Bakelite phone plugged in at the same time that rang as well so bell phones are working already on the line . How do I test for what you suggest ?

27th Jun 2016, 8:42 am	#4
chipp1968 Rest in Peace Join Date: Jul 2006 Location: Somerset, UK. Posts: 2,356	Re: 746 will no longer ring! Well .It now is working..at least in the main socket . It didn't last night . The main socket is in the bedroom . In the extension downstairs it still doesn't ring . Maybe it waste of those double faults ..the wire being loose , yet Im sure it originally did ring down here . I shall take it to neighbours later and see if it works ok there . What could be the wiring problem for it not to work down stairs ?

27th Jun 2016, 10:59 am	#6
mike_newcomb Rest in Peace Join Date: Apr 2012 Location: West London, UK. Posts: 665	Re: 746 will no longer ring! Hi Paul, if the phone works in the master socket, but not in a slave, I would suspect pin 3 is not connected somewhere. Generally 3 to 3 is connected from the master socket onwards, and used for ringing by older phones. By convention 4 to 4 is also connected, although in theory 4 is not used. I had the same problem and was tearing my hair out trying resolve. Eventually I traced th cause to a broadband filter actually missing pins 3 and 4, which I have never seen again, but since as a matter of course check the filters. Regards - Mike

27th Jun 2016, 1:43 pm	#7
chipp1968 Rest in Peace Join Date: Jul 2006 Location: Somerset, UK. Posts: 2,356	Re: 746 will no longer ring! Glad the Hackers good Nick. My main socket has a built in filter ,so I dont think I need any more ? Possibly part of the extension isn't working or wired correctly . I took it to neighbours with no time to test for ring ..But I noted that there was some interference pick up on the line which I didn't get at home .Thats probably because of no filter ?

27th Jun 2016, 2:37 pm	#8
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,866	Re: 746 will no longer ring! Yes, and yes. If it works in the main, filtered socket, the phone is fine, and its your extensionwiring that's been pared-down from 3 to 2 wires; this improves broadband speed but means old phones won't ring. The solution is to use a plug-in microfilter at your neighbours or for your extensions. N.

27th Jun 2016, 3:24 pm	#9
Dave Moll Dekatron Join Date: Feb 2005 Location: West Cumbria (CA13), UK Posts: 6,131	Re: 746 will no longer ring! Just to expand on what Nick says: the use of the microfilter in this instance is not to filter out the broadband (given that you say this is done in your master socket), but because it normally contains its own ring capacitor, therefore putting out the ring current on pin 3. __________________ Mending is better than Ending (cf Brave New World by Aldous Huxley)

27th Jun 2016, 3:31 pm	#10
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,225	Re: 746 will no longer ring! I've not tried this, but it should work.... Let me know if I am right. You should be able to use the ringing capacitor in the 746, which is conneted between T9 and T7. Try : Leave the 3k3 resistor (if you are using one with an old 1k bell) between T4 and T5, if a 4k bell, then leave the strap between T4 and T5. Disconnect the blue wire of the line cord from T6 and 'park' it on a spare terminal, like T14. Strap T6 to T7. (T6 should also be strapped to T5 as before). Strap T8 to T9, and have the red wire of the line cord on there Leave T16-T17-T18-T19 strapped and to the white wire of the line cord.

28th Jun 2016, 7:50 am	#11
chipp1968 Rest in Peace Join Date: Jul 2006 Location: Somerset, UK. Posts: 2,356	Re: 746 will no longer ring! Thank you Tony .A good option to try . Its now at its new home , but they haven't tried it yet for some reason ,so I wont persist until I know it works there or not.

28th Jun 2016, 4:45 pm	#12
Oldcodger Nonode Join Date: Oct 2014 Location: West Midlands, UK. Posts: 2,181	Re: 746 will no longer ring! Something to remember. Many years ago ( feels like centuries now), I was in the process of fitting an extension ( PL1A) to a house. All went well, and at the final test, the main phone ( 700 type) failed to ring. Mad panic- N diagrams out and everything OK. Meter across bell coil showed ringing in ,but bell didn't ring. I made a quick call to the maintenance bloke, who told me that this place had complained several times that the main phone didn't ring at times. Several NFF reports for this one. New phone fitted and problems resolved- it was suggested that phone had polarised bell coil.

29th Jun 2016, 10:55 am	#13
russell_w_b Dekatron Join Date: Jul 2007 Location: Penrith, Cumbria, UK. Posts: 3,687	Re: 746 will no longer ring! Depolarised, may be, but this takes quite a bit of energy to do: typically 5 Amps round forty turns wound into the bar magnet of a 59A bell-movement will demagnetise it sufficiently as to render it inoprative. Less than an Amp in the opposite direction will make it work again. A bell won't normally have d.c. Passing through it to depolarise it in any case. Muck in the armature, maybe? __________________ Regds, Russell W. B. G4YLI. Last edited by russell_w_b; 29th Jun 2016 at 11:03 am.

29th Jun 2016, 8:55 pm	#14
chipp1968 Rest in Peace Join Date: Jul 2006 Location: Somerset, UK. Posts: 2,356	Re: 746 will no longer ring! Well they have tested it and it is working ok in its new home ,so Thanks everyone .