Outdoor Telephone 6745 - bell won't ring.

[Sparks]

I've connected a line cord to this phone. Speech circuit and dialling tone are working but the bell won't ring. In the picture, the line cord is the thick black cable at the bottom.

Red wire to terminal 1, which in turn connects to T8;
White wire to terminal 2, which in turn connects to T18;
Blue wire directly connects to T6.
Green wire not connected.

The bell is a 4000 ohm variant so no 3.3k resistor required. The blue wires from the bell are connected to T4 and T16.

I'd appreciate any help to get this phone ringing. Many thanks.

[russell_w_b]

It seems the circuit diagram is that of a 746, so you could check things out with that? Diagram N846.

What's the d.c. resistance between terminals T6 and T18 'on-hook'?

[russell_w_b]

And is your lead continuity satisfactory from plug to spades on all cores?

[Sparks]

Russell, I've wired it according to instructions on the 'britishtelephones' site. The instructions on there for wiring a 745 are the same as for a 746. My line cord is fully functional. I'm reading no resistance between T6 and T18 on hook.

[WayneL74]

What resistance range is your meter set to? Needs to be at least 4000 ohms. If your meter range goes 200, 2k & 20k ohms it needs to be on the 20k range.

It's possible the bell coil has a break. I bought a 6745 & that was faulty. Try measuring the resistance across each bell coil seperately

[Sparks]

The meter goes from 200 to 2M and it's set on 20k. Each bell coil reads 2.01.

[russell_w_b]

I had a break in a 59A bell-bobbin once but I was lucky because it was right at the solder tag! I managed to re-attach it satisfactorily.

'No resistance'... Does that mean you're seeing a short-cct?

[WayneL74]

That's good news.

Do you get about 4000 ohms if measuring between T4 & T16?

Finally does the bell armature move very freely? It can sometimes corrode where it goes through the case

[Sparks]

'No resistance' means the meter display doesn't change from 1. One bell wire goes to T4, the other to T16. 4.06 measured between these two. The bell armature looks okay and moves freely. The phone itself is very clean - probably never been outside.

One consideration could be the pair of connector blocks at the bottom of the phone, numbered 1/2 and 3/4. 1 is Red and goes to T8 and 2 is White and goes to T18, both as expected. However, 3 is Green and goes to T17, 4 is Blue and goes to T15, both unlike the 746 upon which this board is apparently based!

[WayneL74]

Don't worry about 3 & 4. There appears to be straps from T16 to T19 so the bell is connected one end ok.

Can't quite see what other terminals are strapped but it should be the same as a 746 - T4-T5-T6-T7 & T8-T9

[WayneL74]

Sorry just noticed you have got blue line cord to T6. If that's the case then the strap T6-T7 is not needed.

To simplify things you could try removing the blue line cord & strapping as stated for a 746 above

[Sparks]

T4 and T5 are NOT strapped
T5 and T6 are strapped
T6 and T7 are NOT strapped
T8 and T9 are strapped.

I'm going to have dinner shortly. I shall look in again in about an hour. Thankyou both.

[russell_w_b]

Just start with your meter across the bell-coils (with the phone 'on hook') and, keeping one probe on T4, move the other probe outwards through T16, T17, T18 ultimately to your white plug-in lead and see if you maintain your 4K.

Then do it the other way around. I'm only using drg N846 here, mind - your instrument might be subtly different. Can you trace it out from the PCB tracks off the rear?

[russell_w_b]

Just seen your last post. Have your dinner then strap T4 and T5 and the other strap positions should be OK.

[russell_w_b]

Originally Posted by WayneL74

Can't quite see what other terminals are strapped but it should be the same as a 746 - T4-T5-T6-T7 & T8-T9

There should be a break at an end of the internal capacitor if you're using a plug-in line cord with a master LJU that includes a capacitor, so you'd need to remove either T8-T9 or T6-T7. It would still work, mind, but on a 59D bell (4k) you'd draw fractionally less current.

[Sparks]

Russell, I've re-strapped T4 and T5 and we're now ringing. In most conversions there would of course be a 3.3k resistor to link these two terminals but this particular bell doesn't call for that. Must have been me that took it out without thinking about it.

Many thanks Russell and Wayne.

[russell_w_b]

Phew! Excellent job. Now just to mount it on the living room wall...

[Sparks]

Garden shed, garage or greenhouse. Any will do, provided I ever get to own one of them. BTW, this phone is fitted with a type 16 carbon microphone, which I personally think aren't as inferior as we are led to believe. Are these suitable outdoors or would a type 21 be preferable ?

[russell_w_b]

Originally Posted by Sparks

'...I personally think aren't as inferior as we are led to believe. Are these suitable outdoors or would...'

I think you're right. If it's working with a Transmitter Inset 16 and there are no complaints of crackles, etc... I would just leave it. It's the luck of the draw if you get a good one or a bad one. They're supposed to be protected against moisture and dust ingress but I would watch for terminal corrosion, of course.

[Sparks]

Thanks Russell. I've had a look at your Flickr pages; the Swedish Ericsson telephones stood out as I saw some on TV today.