Quiet or no dial tone in a GPO 706

[Dave Moll]

Originally Posted by Sparks

Apart from the straps from T19/18/17/16, the only connection from T19 is a green wire going to a (I think) capacitor.

According to diagram N806, T19 (A leg via T18) connects to terminal 5 of the switch hook.

edit: Via T17 and T16, it also connects to one end of the bell.

[Sparks]

You're absolutely right Dave. I hope this is something of a breakthrough!

[WayneL74]

Can you now test between T19 & the ASTIC pin 4. It should be a low reading with the switchhooks up & no reading (normally 1. on a digital multimeter) with them down.

If this is the case then you should have continuity from T3 to T19

[Sparks]

Nothing Wayne. The meter doesn't change from 1 with switch up or down.

[WayneL74]

Then this does point to the gravity hook switch or its wiring.

I'm wondering if this is intermittant as the test you did in post 3 between T19 & the brown dial showed continuity.

Do you have any switch cleaner (eg Servisol 10)?

If so I suggest you spray some on a piece of cardboard & run through the contacts again as this seems to be the issue.

Regards,

Wayne

[Sparks]

I'll give them another clean Wayne. In the meantime, can you tell me if all the gravity switches are active and or/relevant with this particular phone, bearing in mind there is no dial ? Ta.

[Sparks]

Still no change after a thorough clean. When the phone is off-hook and there should be a dial tone, the green and brown wires on the switch are connected, likewise the blue and grey. The orange wire is not connected.

Green goes to T7.
Brown goes to the ASTIC only.
Blue goes to T2.
Grey goes to T1.
Orange goes to T5.

T2 and T1 are also the earphone connections in the handset, which theoretically means they would be shorted together when the handset is off hook, hence quiet dial tone. But it wouldn't explain the high side tone.

A real mystery. Thankyou again for your assistance Wayne. I'm going to sleep on this and have another crack tomorrow. Goodnight.

[WayneL74]

The same hookswitch contacts are used whether there is a dial fitted on not

You need to make sure both sets of contacts that are touching which the hookswitch are up are clean.

Then repeat the continuity test between T19 and ASTIC pin 4. Keep cleaning until you get reliable repeatable results

[Sparks]

The switch contacts are clean as a whistle and all fully functional. The T19 aspect is puzzling me. How does this terminal connect to pin 4 on the ASTIC ? I assume there must be an indirect route because, as I noted upthread, the only direct connection to T19 is a green wire going to a capacitor.

[TonyDuell]

There shouldn't be a capacitor connected to T19.

You aren't confusing T9 (right hand terminal in the top row) with T19 (right hand terminal in the bottom row) are you? T9 goes to one side of the 1.8uF capacitor.

What is connected to terminal 4 of the ASTIC? What colour of wire. Trace it (using the meter) to a terminal on the gravity switch (that's where it should go). It's labelled as terminal 4 of the gravity switch in N806, but no idea how the terminals ar numbered. Now find the other terminal on the gravity switch which connects to it when the handset is off-rest. Terminal 5 in N806. What colour of wire is connected there? Where does it go? It should be T19.

[Sparks]

Hello Tony. I'm definitely OK with T9 and T19. There is a brown wire going from T9 to the capacitor and a green wire from T19 to the capacitor, as per the photo below. Admittedly the position of this green wire makes it look like an addition or alteration but I can't say for certain.

There is a brown wire from Pin 4 of the ASTIC to the gravity switch, second from the right in the photo below. It connects to a green wire ( far right of the switch) which goes to T7, not T19. I wonder if this green wire and the green from the capacitor have been accidentally transposed ?

[Sparks]

Pictures as per above post.

[Sparks]

I have to go out now but I shall look in again a bit later this morning. Many thanks everyone.

[Dave Moll]

It sounds as though the two green wires have indeed been transposed. Try swapping them over and see what effect that has.

One side of that double capacitor (1.8μF) should go between T9 and T7, while the other (0.9μF) should go between T10 and one end of R2. I have confirmed this to be the case by looking at the innards of a 706 I have. None of the capacitor's connections should go to T19. That side of the gravity switch should go between T19 and the induction coil.

[Sparks]

Success finally! It was indeed those two green wires being arse about face that caused all this probing and head scratching. Thankyou enormously everyone for your kind patience and persistence.

[Nickthedentist]

Well done everyone! There's very little that goes wrong with these other than wiring faults.

[Sparks]

I was thinking the same the other day, Nick. These old phones are well built with few components but an awful lot of wires crammed into a small space. The odd wiring defect has to be expected, especially with two wires of the same colour.

[pip5678]

Great news Sparks, sounds like your phone is a victim of der Gerfingerpoker, I can put the diagram away now. Cheers Pip

[Dave Moll]

Glad you're now sorted. Well spotted that there were two green wires transposed.

I too have returned my file of diagrams to the shelf!

[Sparks]

Thanks pip and Dave. I think that's all for conversions for now. Just waiting for the wall bracket.