GPO 706 dead

[Chris450d]

Hi everyone,

Recently I've purhcased a gpo 706 and I am trying to convert it to the standard socket we use. However, I have absolutely no tone. The phone seems dead. Components all seem fine on a visual check...

Any ideas what the problem can be or what to look out for?
I have strapped the terminals which usually hold the 3.3K resistor as I have read somewhere that I can do without it...

any help welcomed!

[Station X]

Hello and welcome to the forums.

The first question I must ask is is the the plug and socket wiring in Malta the same as that in the UK. If it isn't then the standard conversion may not work.

There are numerous threads in these forums concerning 706 and 746 phones. Try using the search facility at the top of this page.

[Chris450d]

Hi and thanks,

As far as i know, the british system is the one used locally. In fact we use the same kind of wall sockets. I will check this out tomorrow with our service providers in any case.

Have used the search and came across a bunch of problems which helped me in wiring

[richwk1]

Hi there any chance of a pic of your wiring , might show up your problem.

Rich

[Chris450d]

Photo as requested.

[Station X]

No wonder it doesn't work. The regulator which plugs into the sockets marked A, B, C, D & E is missing. You can simulate a reversed regulator by connecting points B, C and D together.

[Chris450d]

dang. Why on earth was it removed! :s

Will try it soon and get back to you!

Does the wiring seem fine?

[Chris450d]

I soldered points B, C and D together underneath the PCB board and left them connected to the same terminals. That should have worked no?

Still nothing. The only thing I can hear is a faint "click" whenever the receiver buttons are released.

Maybe there is something wrong in the connector socket:

http://www.britishtelephones.com/wir.../oldsocket.jpg

What I did was connect the respective colours together into the new plug (british kind)

So I think everything is in order now I cannot see anything wrong, maybe there is some faulty component :S

[Tim]

Earpeice?

[richwk1]

Originally Posted by Chris450d

Photo as requested.

Hi.
Graham is dead right (no regulator ) and also from memory green wire of line cord goes to T14 not T15 as you have and i also put a strap between T4 and T5 as well.

Regards Rich

[AndiiT]

Hi,
Looking at your picture there should be no coloured leads connected to T11 to T14, as these are designated as spare terminals.

Comparing your telephone to one of my 706s it is difficult to tell but I suspect that the leads that are connected to the above terminals, and also the blue lead connected to T2 should actually be connected to the dial contacts.

When veiwing the dial face down these are fitted in the order, left to right, Orange, Pink, Brown, Slate (Grey), Blue

Regards
Andrew

[Station X]

Colin. Seeing your picture of the connector socket it looks just like a British Post Ofiice Block Terminal No. 52A. This suggests to me that you're trying to hardwire the telephone to the incoming line rather than using it on a plug and socket system.

That being the case you should wire your phone as per the attached diagram. It will be useful in any case, as it shows the wiring to the dial etc.

[Chris450d]

Originally Posted by AndiiT

Hi,
Looking at your picture there should be no coloured leads connected to T11 to T14, as these are designated as spare terminals.

Comparing your telephone to one of my 706s it is difficult to tell but I suspect that the leads that are connected to the above terminals, and also the blue lead connected to T2 should actually be connected to the dial contacts.

When veiwing the dial face down these are fitted in the order, left to right, Orange, Pink, Brown, Slate (Grey), Blue

Regards
Andrew

I do see those coloured wires coming out of the dial but they are soldered onto the pcb in slots D1 etc. under the dial area. I do not know what the other batch of same coloured wires are for!

As with the connector. I stripped the wires from a modern plug and connected the respective colours to the wires in the line cord. Isn't that what is supposed to be done? Can anyone here give me a picture of their 706 circuit wiring and socket wiring?

Thanks so much for all your help! hope to solve this soon!

[Station X]

I do not know what the other batch of same coloured wires are for!

Trace them then. Follow them from the tags back to their source.

I'm still not clear as to whether you're hard wiring this phone to the line or using the standard UK plug and socket system.

Info on the UK plug and socket system here:-

http://www.vintage-radio.info/docs/

Correct wiring shown in post 3 in this thread. It's a 746, but the terminals are wired the same:-

https://www.vintage-radio.net/forum/...ad.php?t=49602

[Station X]

There's something strange about this telephone. It looks to me like five wires have been hardwired to the regulator tracks on the printed circuit board and connected to the terminal board. I would suggest looking at the underside of the PCB or carrying out a continuity check to confirm this.

That being the case I would expect B to go to T3 and E to go to T2. If you connect the wires from B, C and D to T3 and leave the wire from A on a spare tag this should simulate a reversed regulator. See the N806 diagram and this should make things clear.

[Chris450d]

Hi all,

Yesterday at 1am i was back tackling this phone!

Successs!!

I followed the wiring diagram you provided me with and I had a look at some internal shots of converted sets and strapped T8 and T9. I got a pulse.

It's not perfect though. When the receiver buttons are released the phone makes a loud pop from the earpiece (maybe missing the rectifier?) and the dial isn't yet operable.
Will have to sort them out later today but at least I'm certain that it works!!

Thanks so much,

Will post a pic of the current wiring later on today

[Station X]

If you're using this phone on a plug and socket system you won't need a strap from T8 to T9. This strap connects the phone's bell capacitor. If you're using a plug and socket system the capacitor will be in the master jack and the one in the phone can be disconnected.

Remember that diagram N806 shows an UNCONVERTED phone. A converted phone is wired differently. Make sure that the bell coils are wired to T4 and T16.

[Station X]

Correct wiring for a CONVERTED phone is like this:-

Bell Coils:
T4, T16

Handset Cord:
Blue - T3
Red - T1
Green - T2
White - T10

Line Cord:
White - T18
Blue - T6
Red - T8
Green - T15

Strap/Link:
T5 - T6 .
T16 - T17 - T18 - T19.
Resistor:
T4 - T5 (or strap/link these terminals).

Don't forget to connect the wires from the regulator socket as I suggested earlier.

[Chris450d]

Hi again. Seeing that I failed to get this phone to work. I went and bought another 2 phones which looked similar exterior wise.

On closer inspection i noticed a Bell volume control underneath.
When I opened it up it was considerably different. It is not a GPO model however seems quite similar to a 746 model.

The problem is I don't really know what the model it. There is a wiring diagram on the inside of the phone and I could see written "Telephone 7P" and "C.B. Telephone".

on a positive note, I managed to get this work to 'work' with the plug and socket and i get a pulse from the earpiece. However, if i try calling the phone I get a 'number busy' each time and after a while of listening to the pulses through the old phone It goes to a 'busy' tone and even if i click the handset buttons it does not return to the normal pulse.

Dialler still doesn't work and bell doesn't ring, even though these are wired as they should be according to the original diagram.

I tried comparing the circuit to a converted 706/746 phone and arranged some of the wiring to follow suit. however it is not identical to the converted piece.

I will probably have to evaluate the differences in the wiring diagrams and convert by trial and error.

Will upload a pic soon

[Station X]

The phone you show a photo of in post 5 looks like a bog standard 706 to me albeit without the regulator.

If you want to use it as a hardwired phone wire it as per diagram N806.

If you want to use it on a plug and socket system wire it as described in post 18.

Owing to the odd regulator arrangement you will have to connect the wires from the regulator as described in post 15.

Despite being up to 50 years old these phones are extremely robust and relaible. In my experience the only thing that goes wrong with them is that the carbon mics go noisy and the bell armature can rust up. More rarely the switch hooks or dial springs fail to make good contact.

I am still uncertain as to whether you are using this as a hardwired phone or on a plug and socket system. Please tell us and post a picture of how your phone is wired.

Trial and error is not the way to go.