Help needed with 8746 telephone

[JoshWard]

Hi folks,
After many years of wanting an old 'phone I couldn't resist a BT 8746 (updated version of the GPO 746) for £5 today!

I believe this type came with the 'new style' connector plug from new?

The seller was using it up until this year so I decided to give it a try. I discovered that I can ring from it successfully (to my mobile etc), but when I tried to ring it I got a message saying 'the other person is on the phone'.
This could of course be a good thing as it would mean I would not get any spam calls but in case anybody does really need to telephone me I really need to sort it out

Does anybody have any idea on what could be wrong here?

I should add I have no idea about telephones and have never worked with them before.

Thanks in advance,
Josh.

[dagskarlsen]

The UK wiring are a little different from here, but it looks ringer circuit related.
I guess it is a strap connected to T16, try to remove it. The phone will probably not ring, but it sound like that in you cell phone, and if you lift of the handset it will probably establish a connection. Not sure, but its not any risk to try.

dsk

[Nickthedentist]

Hi Josh,

It sounds like the phone is not "hanging up" properly so the exchange thinks the receiver is lifted.

Post a good photo of the inside of the phone showing the PCB and how the straps/handset/line cord are attached, and I'm sure we can sort it out.

Nick.

[Dave Moll]

It may also be worth checking whether the cradle switch is operating correctly.

[JoshWard]

Thanks for the advice. Reading around on various 'phone related sites it appears the wiring colours were standardised in these so here goes....

Line cord connections are:
Red- T8
Blue- T6
Green- T15
White- T18

Handset connections are:
Red- T1
Blue- T3
Green- T2
White- T10

The straps are the wire links aren't they?

If so they run as follows:
One across T4,T5 and T6
One from T16 to T17
One across T17, T18 and T19 (so T16, 17, 18 and 19 are all linked together).

Can't wait to get this up and running!

Josh.

[Nickthedentist]

Josh, your wiring looks fine at a quick glance. Yes, the "straps" are indeed the links.

Unplug it, then connect a resistance meter between the line cord's red and white wires.

With the receiver on-hook (i.e. black buttons held down), what resistance do you get?

Dave's suggestion is very sensible - try operating the microswitch's button directly with your finger.

Nick

[JoshWard]

Hmmmm I'm not sure the switch is operating correctly, there appears to be something missing from the mechanism? I would have expected more downwards movement on the black buttons.

In the second picture I am pressing down on the black buttons but the switch does not appear to be operating, I am guessing when the black buttons are pressed it is meant to look like the third picture?

With the buttons held down (as in picture two) I get 0.5k- this is the same reading I get without pressing the buttons down, with the switch pressed down (as in picture three) I get infinite resistance.

[davidw]

IIRC the switch operating mechanism (Z shaped bit!) is bent. The top of the Z should be higher. A simple tweek upwards will put it right. Should be parallel with the bottom section as in Z. Just a bit of "trial and error" and you will see how it works.
Hope that makes sense.
Was a regular problem when I was "on the tools"

[Nickthedentist]

Originally Posted by JoshWard

there appears to be something missing from the mechanism

Looks complete to me!

Originally Posted by JoshWard

Hmmmm I'm not sure the switch is operating correctly... I am guessing when the black buttons are pressed it is meant to look like the third picture?

Yes!

Originally Posted by JoshWard

With the buttons held down (as in picture two) I get 0.5k- this is the same reading I get without pressing the buttons down, with the switch pressed down (as in picture three) I get infinite resistance.

This points to a mechanical problem with the levers that operates the microswitch. Electrically, everything sounds fine, and I bet it would ring if you held the microswitch down as in pic 3

See here: http://www.samhallas.co.uk/collectio...9_interior.jpg

This makes me think the top bit of the lever has been bent, as circled in my picture. It should be at 90 degrees, as in the Sam Halllas link. Just as DavidW said! I bet it's been dropped.

You're nearly there, Josh...

[JoshWard]

Thanks David and Nick, bent it back into position and it works well

Love that ringing noise! Will put some pics of it up once I've had a chance to clean it up and put a new label in it. Was hoping to do it this evening but I have got to go out and pick up a few new toys (including a Bush VHF64, it's been a good couple of days!!).

Just need a trimphone now

[JoshWard]

Looking much better now

[Nickthedentist]

Glad you got it working!

Probably worth cleaning the dial contacts with a strip of thin card soaked in Servisol if you get any odd symptoms or noises.

Nick.

[JoshWard]

Thanks for the tip!