8746 Fails To Answer On Pickup

[goosegog]

Hi everyone. I'm new here and new to telephone repairs. I do have experience repairing other things, mechanical and electrical, mostly automotive.

May I please have a little advice about my telephone. It's a brown 8746 model which was previously working with me however one day it failed to answer calls.

Upon inspection, the microswitch which is activated when you pick up, can be heard to make two clicks (presumably one to cancel bells, one to answer call?). When you pick up, the bells cease to ring but the call is not answered. Instead, the caller continues to hear the ringing tone. Corresponding clicks can be heard in the 8746's earpiece

I've checked all screw connections are tight and introduced a little WD40 to the microswitch and worked it plenty but still no joy. I haven't tested anything electrical yet though

I hope you can help. Many thanks, Ferg (Dorking, Surrey)

[Dave Moll]

If the off-hook condition is not being recognised, this means that the line impedence is not being reduced when the cradle switch is operated. Although the fault may lie in the switching itself, it is more likely that there is a discontinuity elsewhere in the loop.

One possibility which I would check is that the connections to the transmitter (microphone) in the mouthpiece are all in good order. A quick check of the functioning of the transmitter can be made by blowing into the mouthpiece and checking whether this makes a sound in the receiver (earpiece).

Information about the (8)746 can be found here and a wiring diagram here.

[goosegog]

Thank you for your reply. I don't hear a dial tone nor hear noise when I blow in the mic, presumably because off-hook condition is not being recognised

Many thanks, Fergus

[Dave Moll]

One thought (and I don't know whether this would help) - with the ringing tone still being received at the far end when the handset is lifted, turn the dial on the faulty 'phone and hold it away from its normal position (which will close a set of contacts known as the "dial off-normal" contacts that short out the transmitter and receiver). Does the caller continue to hear the ringing tone?

My only other suggestion would be (with the 'phone disconnected from the line) to use the wiring diagram to identify what should provide continuity between the various parts of the loop path between the "A" leg (T15/16/17/18) and the "B" leg (T8) and check out the actual resistance with a multimeter. Hopefully, this will identify an open-circuit somewhere that should have continuity.

[DAVEHALL]

On 746 from distant memory ,the mechanics to the microswitches tended at times to becme disengauged - very simple one -but does microswitch operate on switch hooks .

[goosegog]

I think I've found the problem. There's a poor connection in the telephone's BT plug between the red wire (T8) and the corresponding pin. I took the handset off the hook, called it on my mobile and though the bells didn't ring, it was ringing on my mobile. When I wigged the wire at the plug, it answered the call. I wiggled it some more and the sound cut in and out. Thanks for your help prompting me to test everything.

Next question, how do I go about getting the plug repaired / renewed?

[AndiiT]

Hi,
The plugs are difficult to repair at the best of times, looking at the pictures of your phone it is already fitted with a "modern" line cord so the best bet would be replacement of this; line cords are often available on eBay, try the Collectables>Radio/Television/Telephony>Telephone section there.

Regards
Andrew

[Dave Moll]

That would certainly fit your symptoms, as a break in the red wire would not affect the ringer - which is connected between white and blue. Lifting the handset disconnects the ringer, but fails to create the loop which the exchange needs to detect the off-hook condition.

[goosegog]

Originally Posted by AndiiT

looking at the pictures of your phone it is already fitted with a "modern" line cord so the best bet would be replacement of this; line cords are often available on eBay

That's a jolly good idea, thanks. 3 metre extension cable on order at 99p, free P&P. I love eBay!

[goosegog]

One fixed telephone! Thanks for your help everyone