GPO 700 Series Problem

[YoungManGW]

Dear all,

I have wired a GPO 700 series phone as follows:
- 205 rectifier between T1 and T2
- 3k3 resistor between T4 and T5
- straps between T5 and T6, T8 and T9, and T16 to T19 inclusive
- handset red to T1, green to T2, blue to T3, white to T10
- linecord blue to T6, red to T8, green to T12, white to T17

I can dial into the 700, which rings, but cannot hear anything, either on the 700 or the phone called from. I cannot dial out from the 700 at all. I have tried removing the Jack at the BT box end and putting this directly into the box, in case the problem was with the splitter at that end, but this made no difference.

I would appreciate any observations and assistance that fellow forum members can provide.

Many thanks,
Richard

[Nickthedentist]

Hi Richard,

Your wiring sounds right, assuming the line cord is conventionally wired - not all are! It is worth checking this out.

The dialling-out problem might be due to your exchange not supporting pulse dialling (or being fussy). Do you have any other rotary phones which work on your line? What happens if you lift the receiver and get a dialling tone, then depress the black handset rest "buttons" briefly? Does the dialling tone remain or go?

As for the other problem, can you hear a dial tone in the 700 phone or not?

Nick.

[Nicklyons2]

First leave the green off. Next - is the cradle switch actually switching; theres a bit of a tortuous linkage (depending on exact model) which can get sprained, or is the switch faulty? If you've a meter put it on a range low K Ohms connect it to A & B lines (Rd & Wh on line cord). If you operate the cradle switch you should get a change from, in effect, open circuit to the DC resistance of the carbon mic. Also you could temporarily remove the rectifier in case it is faulty.

[Dave Moll]

As you don't mention strapping T6 and T7, I assume that you haven't (which is correct), as it is important that one end or other (either T6-T7 or T8-T9) of the internal ringing capacitor is disconnected. This would not, however, explain the reported problem - which sounds more like a fault (either short circuit or open circuit) somewhere in the speech circuit or dial-off-normal switches. Given the stated inability to dial out, I would start by checking for o/c transmitter (mic).

edit: the fact that two other posts were made while I was composing my post shows just how slow I am to post - mostly as a result of double-checking circuit diagrams as I post.

[Nicklyons2]

Oh and I forgot to mention - make sure the dial is wired in correctly . A good preliminary test is with the meter as I described above, then watching the meter dial; does the meter register the pulses as the dial returns?

[YoungManGW]

Thank-you for these suggestions. I shall try these over the next couple of days and then post an update.

To answer the questions asked:
- a previous rotary phone worked when connected to the same BT socket
- I get a dialling tone on lifting the receiver, and this goes on depression of the black rest buttons, and then returns upon release of these
- on seeking to dial out there is a pause after completion of the number and then just a dead tone
- model is a 746
- T6 and T7 are not strapped

Thank-you again. I will have a root about. Regards.

[YoungManGW]

First, a correction: model is a 706, not a 746.

I have so far tried:

1. Leaving off the linecord green.

2. Making sure the cradle linkage is okay - all seems fine.

3. Linecord wiring change of green to T15, white to T18.

4. Further alternative linecord wiring of blue T6, red T8, green T15, white T18, with no strap between T8 and T9.

In all instances the problem remains as described before. The phone will ring when dialled into, but nothing can be heard in the handset, other than one's own words, echoed back. There is a dialling tone upon press and release of the cradle buttons, but completion of the dialled number just results in a continuous tone, no ring tone.

I don't have a meter I'm afraid. Any further thoughts would be welcome. Thank-you.

Regards,
Richard

[Nickthedentist]

Originally Posted by YoungManGW

The phone will ring when dialled into, but nothing can be heard in the handset, other than one's own words, echoed back. There is a dialling tone upon press and release of the cradle buttons, but completion of the dialled number just results in a continuous tone, no ring tone.

OK, Richard, just to clarify:

• The earpiece ("receiver") is definitely working, as you can hear the dialing tone and your own voice ("sidetone") through it.
• Yet, if someone phones you, your 706 rings its bell but when you lift the handset, but you can't hear the other person.

This doesn't really make sense as far as I understand how phones work, so could you double check, please.


Nick.

[Station X]

Continuous tone after dialling sounds like Number Unobtainable Tone (NUT) however many networks now use the announcement "The number you have dialled has not been recognised.............."

Can you "break dial tone" ie if you dial a single digit (say an 8) does the dial tone change to silence?

Without a meter you are probably stuck now.

These phones are very simple devices and I can never understand why people have so much trouble with them, even though they may be 50 years old.

[Nickthedentist]

Originally Posted by YoungManGW

There is a dialling tone upon press and release of the cradle buttons, but completion of the dialled number just results in a continuous tone, no ring tone.

Does the dial tone still persist after a single, sharp, "staccato" tap on the cradle buttons?

EDIT: Sorry, crossed with Graham and realised I hadn't read your reply properly, so I've edited my post.

Originally Posted by Station X

Without a meter you are probably stuck now.

Surely it's time to buy one, Richard! There are so many faults that can be traced and then fixed with so many appliances around the house if you have even the cheapest (£5) meter.

[Station X]

nothing can be heard in the handset, other than one's own words, echoed back

This was called "getting a blow" ie if you blow into the microphone you should hear the blow in the earpiece. Some "sidetone" is necessary or the phone will sound completely dead. This test proves that the transmitter (microphone) and receiver (earpiece) are OK.

If an incoming call is answered can the caller hear you?

[Station X]

A further thought. Try reversing the regulator (plug in PCB). This will render it inoperative and negate the effect of any faults on it.

[YoungManGW]

Nick, your clarifying summary is exactly right. The dial tone remains after a staccato touch on the cradle buttons. Yep, time to get a meter!

Graham, on dialling a single digit on the 706 the dial tone remains. The person calling the 706 is unable to hear me on their phone upon me answering the 706.

Regards,
Richard

[Station X]

Either your phone is not producing dial pulses, or your network isn't accepting them.

Time to get a meter.

[Nickthedentist]

Richard, could you post some clear pictures of how you've wired the phone. It's amazing how sometimes a fresh pair of eyes can spot a problem instantly - though of course, there may be nothing wrong in that respect.

N.

[YoungManGW]

Will do Nick, thank-you, although there will be a bit of a delay, as about to head off for a few days away. Many thanks to all for the welcome assistance thus far.
Regards,
Richard