Converted 746 won't ring

[baznave]

I was recently given a GPO 746 and decided to convert it according to the instructions on britishtelephones.com. It's my first attempt at anything like this but everything went pretty smoothly. I'm getting a good clear reception and can make and receive calls no problem. However I'm getting no ring at all on incoming calls.

I've trawled through loads of helpful advice on this forum but nothing which has fixed my issue. So far I have tried...

• Plugging the phone directly into the main socket with nothing else plugged in
• Trying the phone on a different line (Separate lines coming into the same house, so would be the same exchange)
• Temporarily putting a strap between T4-T5 instead of the resistor.
• Checking the resistance of the bell (it is 1.2, first coil .52 second .5)
• Temporarily strapping T6-T7 and disconnecting the blue line cord

None of these have resulted in a ring, or helped me narrow down the problem. There doesn't seem to be any movement from the bell arm during ringing at all, although I can move it freely by hand so it doesn't appear to be stuck.

Is there anything else I can try to help narrow down the issue?

[Station X]

Hello and welcome to the forums.

Checking the resistance of the bell (it is 1.2, first coil .52 second .5)

I'm afraid that statement is meaningless as you haven't given any units. 1.2 ohms? 1.2 kilohms? Why three readings and not two ie one per coil?

[Dave Moll]

I take this to be 1.2K across the two coils in series, and the individual coils to be 520 ohm and 500 ohm respectively, is that a correct assumption? If so, that is near enough the correct values, and the 3.3K resistor in series would be correct.

[baznave]

Originally Posted by Dave Moll

I take this to be 1.2K across the two coils in series, and the individual coils to be 520 ohm and 500 ohm respectively, is that a correct assumption? If so, that is near enough the correct values, and the 3.3K resistor in series would be correct.

Yup, that's right. Apologies, I should have been clearer.

[russell_w_b]

Originally Posted by baznave

Is there anything else I can try to help narrow down the issue?

Have you a multimeter that will measure a.c. volts and give a meaningful reading from a 400 millisecond burst of ringing current? If so, connect it across the bell-motor connections, clip the cradle-switch down, and ring yourself up. You should see if you have ringing voltage at the bell coils.

If no reading, work backwards by metering terminals T4 and the joined-up terminals T16, 17, 18, 19. You should have ringing voltage here, which will be anything from 75V a.c. downwards.

If still no reading, leave one meter lead connected to joined-up terminals T16, 17, 18, 19 and disconnect the blue wire of your standard BT plug and lead that goes to terminal T5 (or T6) and connect your other meter terminal here, still set to a.c. volts.

By doing this you will be able to tell if you are getting ringing voltage to your telephone. If not, your lead or plug is likely to be faulty (it's not unknown for the plug-end connectors to be open-cct!).

If you only have an ohm-meter or continuity tester, check out your plug and lead for continuity. Looking at your plug with the contacts uppermost and away from you, the lead towards you with the detent-clip on your right you should have pins 2, 3, 4, 5 (1 and 6 aren't used) connected to white, green, blue, red respectively.

Pin 2 should be connected to joined-up terminals 16, 17, 18, 19.
Pin 3 isn't used.
Pin 4 should be connected to terminal 6, joined to 5, with your resistor between 5 and 4.
Pin 5 should be connected to your terminal 8.

Note the plug numbers are opposite to the socket numbers (2 in the plug to 5 in the socket, 3 in the plug to 4 in the socket, etc...).

Do the above and report back.

[baznave]

Originally Posted by russell_w_b

Pin 2 should be connected to joined-up terminals 16, 17, 18, 19.
Pin 3 isn't used.
Pin 4 should be connected to terminal 6, joined to 5, with your resistor between 5 and 4.
Pin 5 should be connected to your terminal 8.

Note the plug numbers are opposite to the socket numbers

Problem solved. I had in fact wired the plug back to front. I was using a salvaged phone lead with black, red, green and yellow wires rather than the BT standard, and matched the colours up using this guide http://www.britishtelephones.com/pstconv2.htm. I should have double checked the pins end to end to begin with rather than assuming.

Many thanks for helping me sort this out

[matthewhouse]

Originally Posted by baznave

I was using a salvaged phone lead with black, red, green and yellow wires rather than the BT standard...

That's funny I did exactly the same thing, I ended up belling out the lead to work out what needed to go where. Is that diagram incorrect or are there just several standard non-standard leads?

[russell_w_b]

Originally Posted by matthewhouse

Is that diagram incorrect or are there just several standard non-standard leads?

I would only trust the standard-issue BT replacement, as I've come across different configurations in the past. It's always better to buzz out the leads anyway, rather than go by colour, as it eliminates any doubt.

I have also come across rogue IDC connections at the plug-end, where the little connector hasn't been pushed home properly! Buzzing out the wires will turn up this fault as well, if present.

A quick check can be made, if meterless but in posession of a torch, by shining a light underneath the plug to reveal the wiring colours. Works better on some than others.

[baznave]

Originally Posted by matthewhouse

Is that diagram incorrect or are there just several standard non-standard leads?

I have three identical looking leads which I've just tested, and one is wired as in the diagram (black to pin 2), and the other two are reversed. I guess the moral is always to check which pin goes to which wire.